| Message ID | 20210304155144.3.I60a7fb23ce4589006bc95c64ab8d15c74b876e68@changeid (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | [1/3] drm/bridge: ti-sn65dsi86: Simplify refclk handling | expand |
On Thu 04 Mar 17:52 CST 2021, Douglas Anderson wrote: > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > EDID from the panel. That commit kinda worked but it had some serious > problems. > > The problems all stem from the fact that userspace wants to be able to > read the EDID before it explicitly enables the panel. For eDP panels, > though, we don't actually power the panel up until the pre-enable > stage and the pre-enable call happens right before the enable call > with no way to interject in-between. For eDP panels, you can't read > the EDID until you power the panel. The result was that > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > (falling back to what drm_panel_get_modes() returned) until _after_ > the EDID was needed. > > To make it concrete, on my system I saw this happen: > 1. We'd attach the bridge. > 2. Userspace would ask for the EDID (several times). We'd try but fail > to read the EDID over and over again and fall back to the hardcoded > modes. > 3. Userspace would decide on a mode based only on the hardcoded modes. > 4. Userspace would ask to turn the panel on. > 5. Userspace would (eventually) check the modes again (in Chrome OS > this happens on the handoff from the boot splash screen to the > browser). Now we'd read them properly and, if they were different, > userspace would request to change the mode. > > The fact that userspace would always end up using the hardcoded modes > at first significantly decreases the benefit of the EDID > reading. Also: if the modes were even a tiny bit different we'd end up > doing a wasteful modeset and at boot. > > As a side note: at least early EDID read failures were relatively > fast. Though the old ti_sn_bridge_connector_get_modes() did call > pm_runtime_get_sync() it didn't program the important "HPD_DISABLE" > bit. That meant that all the AUX transfers failed pretty quickly. > > In any case, enough about the problem. How are we fixing it? Obviously > we need to power the panel on _before_ reading the EDID, but how? It > turns out that there's really no problem with just doing all the work > of our pre_enable() function right at attach time and reading the EDID > right away. We'll do that. It's not as easy as it sounds, though, > because: > > 1. Powering the panel up and down is a pretty expensive operation. Not > only do we need to wait for the HPD line which seems to take up to > 200 ms on most panels, but also most panels say that once you power > them off you need to wait at least 500 ms before powering them on > again. We really don't want to incur 700 ms of time here. > > 2. If we happen not to have a fixed "refclk" we've got a > chicken-and-egg problem. We seem to need the clock setup to read > the EDID. Without a fixed "refclk", though, the bridge runs with > the MIPI pixel clock which means you've got to use a hardcoded mode > for the MIPI pixel clock. > > We'll solve problem #1 above by leaving the panel powered on for a > little while after we read the EDID. If enough time passes and nobody > turns the panel on then we'll undo our work. NOTE: there are no > functional problems if someone turns the panel on after a long delay, > it just might take a little longer to turn on. > > We'll solve problem #2 by simply _always_ using a hardcoded mode (not > reading the EDID) if a "refclk" wasn't provided. While it might be > possible to fudge something together to support this, it's my belief > that nobody is using this mode in real life since it's really > inflexible. I saw it used for some really early prototype hardware > that was thrown in the e-waste bin years ago when we realized how > inflexible it was. In any case, if someone is using this they're in no > worse shape than they were before the (fairly recent) commit > 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC"). > > NOTE: while this patch feels a bit hackish, I'm not sure there's much > we can do better without a more fundamental DRM API change. After > looking at it a bunch, it also doesn't feel as hacky to me as I first > thought. The things that pre-enable does are well defined and well > understood and there should be no problems with doing them early nor > with doing them before userspace requests anything. > > Fixes: 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC") > Signed-off-by: Douglas Anderson <dianders@chromium.org> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org> Regards, Bjorn > --- > > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 98 ++++++++++++++++++++++++--- > 1 file changed, 88 insertions(+), 10 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > index 491c9c4f32d1..af3fb4657af6 100644 > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > @@ -16,6 +16,7 @@ > #include <linux/pm_runtime.h> > #include <linux/regmap.h> > #include <linux/regulator/consumer.h> > +#include <linux/workqueue.h> > > #include <asm/unaligned.h> > > @@ -130,6 +131,12 @@ > * @ln_assign: Value to program to the LN_ASSIGN register. > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > * > + * @pre_enabled_early: If true we did an early pre_enable at attach. > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > + * if a normal pre_enable never came. > + * @pre_enable_mutex: Lock to synchronize between the pre_enable_timeout_work > + * and normal mechanisms. > + * > * @gchip: If we expose our GPIOs, this is used. > * @gchip_output: A cache of whether we've set GPIOs to output. This > * serves double-duty of keeping track of the direction and > @@ -158,6 +165,10 @@ struct ti_sn_bridge { > u8 ln_assign; > u8 ln_polrs; > > + bool pre_enabled_early; > + struct delayed_work pre_enable_timeout_work; > + struct mutex pre_enable_mutex; > + > #if defined(CONFIG_OF_GPIO) > struct gpio_chip gchip; > DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS); > @@ -272,12 +283,6 @@ static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector) > struct edid *edid = pdata->edid; > int num, ret; > > - if (!edid) { > - pm_runtime_get_sync(pdata->dev); > - edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc); > - pm_runtime_put(pdata->dev); > - } > - > if (edid && drm_edid_is_valid(edid)) { > ret = drm_connector_update_edid_property(connector, edid); > if (!ret) { > @@ -412,10 +417,8 @@ static void ti_sn_bridge_post_disable(struct drm_bridge *bridge) > pm_runtime_put_sync(pdata->dev); > } > > -static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) > +static void __ti_sn_bridge_pre_enable(struct ti_sn_bridge *pdata) > { > - struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > - > pm_runtime_get_sync(pdata->dev); > > /* configure bridge ref_clk */ > @@ -443,6 +446,38 @@ static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) > drm_panel_prepare(pdata->panel); > } > > +static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) > +{ > + struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > + > + mutex_lock(&pdata->pre_enable_mutex); > + if (pdata->pre_enabled_early) > + /* Already done! Just mark that normal pre_enable happened */ > + pdata->pre_enabled_early = false; > + else > + __ti_sn_bridge_pre_enable(pdata); > + mutex_unlock(&pdata->pre_enable_mutex); > +} > + > +static void ti_sn_bridge_cancel_early_pre_enable(struct ti_sn_bridge *pdata) > +{ > + mutex_lock(&pdata->pre_enable_mutex); > + if (pdata->pre_enabled_early) { > + pdata->pre_enabled_early = false; > + ti_sn_bridge_post_disable(&pdata->bridge); > + } > + mutex_unlock(&pdata->pre_enable_mutex); > +} > + > +static void ti_sn_bridge_pre_enable_timeout(struct work_struct *work) > +{ > + struct delayed_work *dwork = to_delayed_work(work); > + struct ti_sn_bridge *pdata = container_of(dwork, struct ti_sn_bridge, > + pre_enable_timeout_work); > + > + ti_sn_bridge_cancel_early_pre_enable(pdata); > +} > + > static int ti_sn_bridge_attach(struct drm_bridge *bridge, > enum drm_bridge_attach_flags flags) > { > @@ -516,6 +551,34 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge, > } > pdata->dsi = dsi; > > + /* > + * If we have a refclk then we can support dynamic EDID. > + * > + * A few notes: > + * - From trial and error it appears that we need our clock setup in > + * order to read the EDID. If we don't have refclk then we > + * (presumably) need the MIPI clock on, but turning that on implies > + * knowing the pixel clock / not needing the EDID. Maybe we could > + * futz this if necessary, but for now we won't. > + * - In order to read the EDID we need power on to the bridge and > + * the panel (and it has to finish booting up / assert HPD). This > + * is slow so we leave the panel powered when we're done but setup a > + * timeout so we don't leave it on forever. > + * - The rest of Linux assumes that it can read the EDID without > + * (explicitly) enabling the power which is why this somewhat awkward > + * step is needed. > + */ > + if (pdata->refclk) { > + mutex_lock(&pdata->pre_enable_mutex); > + > + pdata->pre_enabled_early = true; > + __ti_sn_bridge_pre_enable(pdata); > + pdata->edid = drm_get_edid(&pdata->connector, &pdata->aux.ddc); > + schedule_delayed_work(&pdata->pre_enable_timeout_work, 30 * HZ); > + > + mutex_unlock(&pdata->pre_enable_mutex); > + } > + > return 0; > > err_dsi_attach: > @@ -525,6 +588,17 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge, > return ret; > } > > +static void ti_sn_bridge_detach(struct drm_bridge *bridge) > +{ > + struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > + > + cancel_delayed_work_sync(&pdata->pre_enable_timeout_work); > + ti_sn_bridge_cancel_early_pre_enable(pdata); > + > + kfree(pdata->edid); > + pdata->edid = NULL; > +} > + > static void ti_sn_bridge_disable(struct drm_bridge *bridge) > { > struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > @@ -863,6 +937,7 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge) > > static const struct drm_bridge_funcs ti_sn_bridge_funcs = { > .attach = ti_sn_bridge_attach, > + .detach = ti_sn_bridge_detach, > .pre_enable = ti_sn_bridge_pre_enable, > .enable = ti_sn_bridge_enable, > .disable = ti_sn_bridge_disable, > @@ -1227,6 +1302,10 @@ static int ti_sn_bridge_probe(struct i2c_client *client, > if (!pdata) > return -ENOMEM; > > + mutex_init(&pdata->pre_enable_mutex); > + INIT_DELAYED_WORK(&pdata->pre_enable_timeout_work, > + ti_sn_bridge_pre_enable_timeout); > + > pdata->regmap = devm_regmap_init_i2c(client, > &ti_sn_bridge_regmap_config); > if (IS_ERR(pdata->regmap)) { > @@ -1301,7 +1380,6 @@ static int ti_sn_bridge_remove(struct i2c_client *client) > if (!pdata) > return -EINVAL; > > - kfree(pdata->edid); > ti_sn_debugfs_remove(pdata); > > of_node_put(pdata->host_node); > -- > 2.30.1.766.gb4fecdf3b7-goog >
Hi Doug, Thank you for the patch. On Thu, Mar 04, 2021 at 03:52:01PM -0800, Douglas Anderson wrote: > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > EDID from the panel. That commit kinda worked but it had some serious > problems. > > The problems all stem from the fact that userspace wants to be able to > read the EDID before it explicitly enables the panel. For eDP panels, > though, we don't actually power the panel up until the pre-enable > stage and the pre-enable call happens right before the enable call > with no way to interject in-between. For eDP panels, you can't read > the EDID until you power the panel. The result was that > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > (falling back to what drm_panel_get_modes() returned) until _after_ > the EDID was needed. > > To make it concrete, on my system I saw this happen: > 1. We'd attach the bridge. > 2. Userspace would ask for the EDID (several times). We'd try but fail > to read the EDID over and over again and fall back to the hardcoded > modes. > 3. Userspace would decide on a mode based only on the hardcoded modes. > 4. Userspace would ask to turn the panel on. > 5. Userspace would (eventually) check the modes again (in Chrome OS > this happens on the handoff from the boot splash screen to the > browser). Now we'd read them properly and, if they were different, > userspace would request to change the mode. > > The fact that userspace would always end up using the hardcoded modes > at first significantly decreases the benefit of the EDID > reading. Also: if the modes were even a tiny bit different we'd end up > doing a wasteful modeset and at boot. s/and at/at/ ? > As a side note: at least early EDID read failures were relatively > fast. Though the old ti_sn_bridge_connector_get_modes() did call > pm_runtime_get_sync() it didn't program the important "HPD_DISABLE" > bit. That meant that all the AUX transfers failed pretty quickly. > > In any case, enough about the problem. How are we fixing it? Obviously > we need to power the panel on _before_ reading the EDID, but how? It > turns out that there's really no problem with just doing all the work > of our pre_enable() function right at attach time and reading the EDID > right away. We'll do that. It's not as easy as it sounds, though, > because: > > 1. Powering the panel up and down is a pretty expensive operation. Not > only do we need to wait for the HPD line which seems to take up to > 200 ms on most panels, but also most panels say that once you power > them off you need to wait at least 500 ms before powering them on > again. We really don't want to incur 700 ms of time here. > > 2. If we happen not to have a fixed "refclk" we've got a > chicken-and-egg problem. We seem to need the clock setup to read > the EDID. Without a fixed "refclk", though, the bridge runs with > the MIPI pixel clock which means you've got to use a hardcoded mode > for the MIPI pixel clock. > > We'll solve problem #1 above by leaving the panel powered on for a > little while after we read the EDID. If enough time passes and nobody > turns the panel on then we'll undo our work. NOTE: there are no > functional problems if someone turns the panel on after a long delay, > it just might take a little longer to turn on. > > We'll solve problem #2 by simply _always_ using a hardcoded mode (not > reading the EDID) if a "refclk" wasn't provided. While it might be > possible to fudge something together to support this, it's my belief > that nobody is using this mode in real life since it's really > inflexible. I saw it used for some really early prototype hardware > that was thrown in the e-waste bin years ago when we realized how > inflexible it was. In any case, if someone is using this they're in no > worse shape than they were before the (fairly recent) commit > 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC"). > > NOTE: while this patch feels a bit hackish, I'm not sure there's much > we can do better without a more fundamental DRM API change. After > looking at it a bunch, it also doesn't feel as hacky to me as I first > thought. The things that pre-enable does are well defined and well > understood and there should be no problems with doing them early nor > with doing them before userspace requests anything. > > Fixes: 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC") > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- > > drivers/gpu/drm/bridge/ti-sn65dsi86.c | 98 ++++++++++++++++++++++++--- > 1 file changed, 88 insertions(+), 10 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > index 491c9c4f32d1..af3fb4657af6 100644 > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > @@ -16,6 +16,7 @@ > #include <linux/pm_runtime.h> > #include <linux/regmap.h> > #include <linux/regulator/consumer.h> > +#include <linux/workqueue.h> > > #include <asm/unaligned.h> > > @@ -130,6 +131,12 @@ > * @ln_assign: Value to program to the LN_ASSIGN register. > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > * > + * @pre_enabled_early: If true we did an early pre_enable at attach. > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > + * if a normal pre_enable never came. Could we simplify this by using the runtime PM autosuspend feature ? The configuration of the bridge would be moved from pre_enable to the PM runtime resume handler, the clk_disable_unprepare() call moved from post_disable to the runtime suspend handler, and the work queue replaced by usage of pm_runtime_put_autosuspend(). > + * @pre_enable_mutex: Lock to synchronize between the pre_enable_timeout_work > + * and normal mechanisms. > + * > * @gchip: If we expose our GPIOs, this is used. > * @gchip_output: A cache of whether we've set GPIOs to output. This > * serves double-duty of keeping track of the direction and > @@ -158,6 +165,10 @@ struct ti_sn_bridge { > u8 ln_assign; > u8 ln_polrs; > > + bool pre_enabled_early; > + struct delayed_work pre_enable_timeout_work; > + struct mutex pre_enable_mutex; > + > #if defined(CONFIG_OF_GPIO) > struct gpio_chip gchip; > DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS); > @@ -272,12 +283,6 @@ static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector) > struct edid *edid = pdata->edid; > int num, ret; > > - if (!edid) { > - pm_runtime_get_sync(pdata->dev); > - edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc); > - pm_runtime_put(pdata->dev); > - } > - > if (edid && drm_edid_is_valid(edid)) { > ret = drm_connector_update_edid_property(connector, edid); > if (!ret) { > @@ -412,10 +417,8 @@ static void ti_sn_bridge_post_disable(struct drm_bridge *bridge) > pm_runtime_put_sync(pdata->dev); > } > > -static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) > +static void __ti_sn_bridge_pre_enable(struct ti_sn_bridge *pdata) > { > - struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > - > pm_runtime_get_sync(pdata->dev); > > /* configure bridge ref_clk */ > @@ -443,6 +446,38 @@ static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) > drm_panel_prepare(pdata->panel); > } > > +static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) > +{ > + struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > + > + mutex_lock(&pdata->pre_enable_mutex); > + if (pdata->pre_enabled_early) > + /* Already done! Just mark that normal pre_enable happened */ > + pdata->pre_enabled_early = false; > + else > + __ti_sn_bridge_pre_enable(pdata); > + mutex_unlock(&pdata->pre_enable_mutex); > +} > + > +static void ti_sn_bridge_cancel_early_pre_enable(struct ti_sn_bridge *pdata) > +{ > + mutex_lock(&pdata->pre_enable_mutex); > + if (pdata->pre_enabled_early) { > + pdata->pre_enabled_early = false; > + ti_sn_bridge_post_disable(&pdata->bridge); > + } > + mutex_unlock(&pdata->pre_enable_mutex); > +} > + > +static void ti_sn_bridge_pre_enable_timeout(struct work_struct *work) > +{ > + struct delayed_work *dwork = to_delayed_work(work); > + struct ti_sn_bridge *pdata = container_of(dwork, struct ti_sn_bridge, > + pre_enable_timeout_work); > + > + ti_sn_bridge_cancel_early_pre_enable(pdata); > +} > + > static int ti_sn_bridge_attach(struct drm_bridge *bridge, > enum drm_bridge_attach_flags flags) > { > @@ -516,6 +551,34 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge, > } > pdata->dsi = dsi; > > + /* > + * If we have a refclk then we can support dynamic EDID. > + * > + * A few notes: > + * - From trial and error it appears that we need our clock setup in > + * order to read the EDID. If we don't have refclk then we > + * (presumably) need the MIPI clock on, but turning that on implies > + * knowing the pixel clock / not needing the EDID. Maybe we could > + * futz this if necessary, but for now we won't. > + * - In order to read the EDID we need power on to the bridge and > + * the panel (and it has to finish booting up / assert HPD). This > + * is slow so we leave the panel powered when we're done but setup a > + * timeout so we don't leave it on forever. > + * - The rest of Linux assumes that it can read the EDID without > + * (explicitly) enabling the power which is why this somewhat awkward > + * step is needed. > + */ > + if (pdata->refclk) { > + mutex_lock(&pdata->pre_enable_mutex); > + > + pdata->pre_enabled_early = true; > + __ti_sn_bridge_pre_enable(pdata); > + pdata->edid = drm_get_edid(&pdata->connector, &pdata->aux.ddc); > + schedule_delayed_work(&pdata->pre_enable_timeout_work, 30 * HZ); > + > + mutex_unlock(&pdata->pre_enable_mutex); > + } > + > return 0; > > err_dsi_attach: > @@ -525,6 +588,17 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge, > return ret; > } > > +static void ti_sn_bridge_detach(struct drm_bridge *bridge) > +{ > + struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > + > + cancel_delayed_work_sync(&pdata->pre_enable_timeout_work); > + ti_sn_bridge_cancel_early_pre_enable(pdata); > + > + kfree(pdata->edid); > + pdata->edid = NULL; > +} > + > static void ti_sn_bridge_disable(struct drm_bridge *bridge) > { > struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); > @@ -863,6 +937,7 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge) > > static const struct drm_bridge_funcs ti_sn_bridge_funcs = { > .attach = ti_sn_bridge_attach, > + .detach = ti_sn_bridge_detach, > .pre_enable = ti_sn_bridge_pre_enable, > .enable = ti_sn_bridge_enable, > .disable = ti_sn_bridge_disable, > @@ -1227,6 +1302,10 @@ static int ti_sn_bridge_probe(struct i2c_client *client, > if (!pdata) > return -ENOMEM; > > + mutex_init(&pdata->pre_enable_mutex); > + INIT_DELAYED_WORK(&pdata->pre_enable_timeout_work, > + ti_sn_bridge_pre_enable_timeout); > + > pdata->regmap = devm_regmap_init_i2c(client, > &ti_sn_bridge_regmap_config); > if (IS_ERR(pdata->regmap)) { > @@ -1301,7 +1380,6 @@ static int ti_sn_bridge_remove(struct i2c_client *client) > if (!pdata) > return -EINVAL; > > - kfree(pdata->edid); > ti_sn_debugfs_remove(pdata); > > of_node_put(pdata->host_node);
Hi, On Sat, Mar 13, 2021 at 1:17 PM Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > > Hi Doug, > > Thank you for the patch. > > On Thu, Mar 04, 2021 at 03:52:01PM -0800, Douglas Anderson wrote: > > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > > EDID from the panel. That commit kinda worked but it had some serious > > problems. > > > > The problems all stem from the fact that userspace wants to be able to > > read the EDID before it explicitly enables the panel. For eDP panels, > > though, we don't actually power the panel up until the pre-enable > > stage and the pre-enable call happens right before the enable call > > with no way to interject in-between. For eDP panels, you can't read > > the EDID until you power the panel. The result was that > > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > > (falling back to what drm_panel_get_modes() returned) until _after_ > > the EDID was needed. > > > > To make it concrete, on my system I saw this happen: > > 1. We'd attach the bridge. > > 2. Userspace would ask for the EDID (several times). We'd try but fail > > to read the EDID over and over again and fall back to the hardcoded > > modes. > > 3. Userspace would decide on a mode based only on the hardcoded modes. > > 4. Userspace would ask to turn the panel on. > > 5. Userspace would (eventually) check the modes again (in Chrome OS > > this happens on the handoff from the boot splash screen to the > > browser). Now we'd read them properly and, if they were different, > > userspace would request to change the mode. > > > > The fact that userspace would always end up using the hardcoded modes > > at first significantly decreases the benefit of the EDID > > reading. Also: if the modes were even a tiny bit different we'd end up > > doing a wasteful modeset and at boot. > > s/and at/at/ ? Sure, I can correct if/when I respin or it can be corrected when landed. > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > index 491c9c4f32d1..af3fb4657af6 100644 > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > @@ -16,6 +16,7 @@ > > #include <linux/pm_runtime.h> > > #include <linux/regmap.h> > > #include <linux/regulator/consumer.h> > > +#include <linux/workqueue.h> > > > > #include <asm/unaligned.h> > > > > @@ -130,6 +131,12 @@ > > * @ln_assign: Value to program to the LN_ASSIGN register. > > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > > * > > + * @pre_enabled_early: If true we did an early pre_enable at attach. > > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > > + * if a normal pre_enable never came. > > Could we simplify this by using the runtime PM autosuspend feature ? The > configuration of the bridge would be moved from pre_enable to the PM > runtime resume handler, the clk_disable_unprepare() call moved from > post_disable to the runtime suspend handler, and the work queue replaced > by usage of pm_runtime_put_autosuspend(). It's an interesting idea but I don't think I can make it work, at least not in a generic enough way. Specifically we can also use this bridge chip as a generic GPIO provider in Linux. When someone asks us to read a GPIO then we have to power the bridge on (pm_runtime_get_sync()) and when someone asks us to configure a GPIO as an output then we actually leave the bridge powered until they stop requesting it as an output. At the moment the only user of this functionality (that I know of) is for the HPD pin on trogdor boards (long story about why we don't use the dedicated HPD) but the API supports using these GPIOs for anything and I've tested that it works. It wouldn't be great to have to keep the panel on in order to access the GPIOs. The other problem is that I think the time scales are different. At boot time I think we'd want to leave the panel on for tens of seconds to give userspace a chance to start up and configure the panel. After userspace starts up I think we'd want autosuspend to be much faster. This could probably be solved by tweaking the runtime delay in code but I didn't fully dig because of the above problem. -Doug
Hi Doug, On Mon, Mar 15, 2021 at 09:25:37AM -0700, Doug Anderson wrote: > On Sat, Mar 13, 2021 at 1:17 PM Laurent Pinchart wrote: > > On Thu, Mar 04, 2021 at 03:52:01PM -0800, Douglas Anderson wrote: > > > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > > > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > > > EDID from the panel. That commit kinda worked but it had some serious > > > problems. > > > > > > The problems all stem from the fact that userspace wants to be able to > > > read the EDID before it explicitly enables the panel. For eDP panels, > > > though, we don't actually power the panel up until the pre-enable > > > stage and the pre-enable call happens right before the enable call > > > with no way to interject in-between. For eDP panels, you can't read > > > the EDID until you power the panel. The result was that > > > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > > > (falling back to what drm_panel_get_modes() returned) until _after_ > > > the EDID was needed. > > > > > > To make it concrete, on my system I saw this happen: > > > 1. We'd attach the bridge. > > > 2. Userspace would ask for the EDID (several times). We'd try but fail > > > to read the EDID over and over again and fall back to the hardcoded > > > modes. > > > 3. Userspace would decide on a mode based only on the hardcoded modes. > > > 4. Userspace would ask to turn the panel on. > > > 5. Userspace would (eventually) check the modes again (in Chrome OS > > > this happens on the handoff from the boot splash screen to the > > > browser). Now we'd read them properly and, if they were different, > > > userspace would request to change the mode. > > > > > > The fact that userspace would always end up using the hardcoded modes > > > at first significantly decreases the benefit of the EDID > > > reading. Also: if the modes were even a tiny bit different we'd end up > > > doing a wasteful modeset and at boot. > > > > s/and at/at/ ? > > Sure, I can correct if/when I respin or it can be corrected when landed. > > > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > index 491c9c4f32d1..af3fb4657af6 100644 > > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > @@ -16,6 +16,7 @@ > > > #include <linux/pm_runtime.h> > > > #include <linux/regmap.h> > > > #include <linux/regulator/consumer.h> > > > +#include <linux/workqueue.h> > > > > > > #include <asm/unaligned.h> > > > > > > @@ -130,6 +131,12 @@ > > > * @ln_assign: Value to program to the LN_ASSIGN register. > > > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > > > * > > > + * @pre_enabled_early: If true we did an early pre_enable at attach. > > > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > > > + * if a normal pre_enable never came. > > > > Could we simplify this by using the runtime PM autosuspend feature ? The > > configuration of the bridge would be moved from pre_enable to the PM > > runtime resume handler, the clk_disable_unprepare() call moved from > > post_disable to the runtime suspend handler, and the work queue replaced > > by usage of pm_runtime_put_autosuspend(). > > It's an interesting idea but I don't think I can make it work, at > least not in a generic enough way. Specifically we can also use this > bridge chip as a generic GPIO provider in Linux. When someone asks us > to read a GPIO then we have to power the bridge on > (pm_runtime_get_sync()) and when someone asks us to configure a GPIO > as an output then we actually leave the bridge powered until they stop > requesting it as an output. At the moment the only user of this > functionality (that I know of) is for the HPD pin on trogdor boards > (long story about why we don't use the dedicated HPD) but the API > supports using these GPIOs for anything and I've tested that it works. > It wouldn't be great to have to keep the panel on in order to access > the GPIOs. The issue you're trying to fix doesn't seem specific to this bridge, so handling it in the bridge driver bothers me :-S Is there any way we could handle this in the DRM core ? I don't want to see similar implementations duplicated in all HDMI/DP bridges. > The other problem is that I think the time scales are different. At > boot time I think we'd want to leave the panel on for tens of seconds > to give userspace a chance to start up and configure the panel. After > userspace starts up I think we'd want autosuspend to be much faster. > This could probably be solved by tweaking the runtime delay in code > but I didn't fully dig because of the above problem.
Hi, On Tue, Mar 16, 2021 at 2:46 PM Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote: > > Hi Doug, > > On Mon, Mar 15, 2021 at 09:25:37AM -0700, Doug Anderson wrote: > > On Sat, Mar 13, 2021 at 1:17 PM Laurent Pinchart wrote: > > > On Thu, Mar 04, 2021 at 03:52:01PM -0800, Douglas Anderson wrote: > > > > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > > > > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > > > > EDID from the panel. That commit kinda worked but it had some serious > > > > problems. > > > > > > > > The problems all stem from the fact that userspace wants to be able to > > > > read the EDID before it explicitly enables the panel. For eDP panels, > > > > though, we don't actually power the panel up until the pre-enable > > > > stage and the pre-enable call happens right before the enable call > > > > with no way to interject in-between. For eDP panels, you can't read > > > > the EDID until you power the panel. The result was that > > > > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > > > > (falling back to what drm_panel_get_modes() returned) until _after_ > > > > the EDID was needed. > > > > > > > > To make it concrete, on my system I saw this happen: > > > > 1. We'd attach the bridge. > > > > 2. Userspace would ask for the EDID (several times). We'd try but fail > > > > to read the EDID over and over again and fall back to the hardcoded > > > > modes. > > > > 3. Userspace would decide on a mode based only on the hardcoded modes. > > > > 4. Userspace would ask to turn the panel on. > > > > 5. Userspace would (eventually) check the modes again (in Chrome OS > > > > this happens on the handoff from the boot splash screen to the > > > > browser). Now we'd read them properly and, if they were different, > > > > userspace would request to change the mode. > > > > > > > > The fact that userspace would always end up using the hardcoded modes > > > > at first significantly decreases the benefit of the EDID > > > > reading. Also: if the modes were even a tiny bit different we'd end up > > > > doing a wasteful modeset and at boot. > > > > > > s/and at/at/ ? > > > > Sure, I can correct if/when I respin or it can be corrected when landed. > > > > > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > index 491c9c4f32d1..af3fb4657af6 100644 > > > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > @@ -16,6 +16,7 @@ > > > > #include <linux/pm_runtime.h> > > > > #include <linux/regmap.h> > > > > #include <linux/regulator/consumer.h> > > > > +#include <linux/workqueue.h> > > > > > > > > #include <asm/unaligned.h> > > > > > > > > @@ -130,6 +131,12 @@ > > > > * @ln_assign: Value to program to the LN_ASSIGN register. > > > > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > > > > * > > > > + * @pre_enabled_early: If true we did an early pre_enable at attach. > > > > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > > > > + * if a normal pre_enable never came. > > > > > > Could we simplify this by using the runtime PM autosuspend feature ? The > > > configuration of the bridge would be moved from pre_enable to the PM > > > runtime resume handler, the clk_disable_unprepare() call moved from > > > post_disable to the runtime suspend handler, and the work queue replaced > > > by usage of pm_runtime_put_autosuspend(). > > > > It's an interesting idea but I don't think I can make it work, at > > least not in a generic enough way. Specifically we can also use this > > bridge chip as a generic GPIO provider in Linux. When someone asks us > > to read a GPIO then we have to power the bridge on > > (pm_runtime_get_sync()) and when someone asks us to configure a GPIO > > as an output then we actually leave the bridge powered until they stop > > requesting it as an output. At the moment the only user of this > > functionality (that I know of) is for the HPD pin on trogdor boards > > (long story about why we don't use the dedicated HPD) but the API > > supports using these GPIOs for anything and I've tested that it works. > > It wouldn't be great to have to keep the panel on in order to access > > the GPIOs. > > The issue you're trying to fix doesn't seem specific to this bridge, so > handling it in the bridge driver bothers me :-S Is there any way we > could handle this in the DRM core ? I don't want to see similar > implementations duplicated in all HDMI/DP bridges. Yes, it is true that this problem could affect other drivers. ...and in full disclosure I think there are other similar workarounds already present. I haven't personally worked on those chips, but in ps8640_bridge_get_edid() there is a somewhat similar workaround to chain a pre-enable (though maybe it's not quite as optimized?). I'm told that maybe something had to be handled for anx7625 (in anx7625_get_edid()?) but that definitely doesn't look at all like it's doing a pre-enable, so maybe things for that bridge just work differently. One thing that makes me hesitant about trying to moving this to the core is that even in sn65dsi86 there is a case where it won't work. As I mentioned in the patch I'm not aware of anyone using it in production, but if someone was using the MIPI clock as input to the bridge chip instead of a fixed "refclk" then trying to get the EDID after just "pre-enable" falls over. Said another way: I can say that with this particular bridge chip, if you're using a fixed refclk, you can read the EDID after the pre-enable. I don't know if that's always true with all other bridge chips. So I guess in summary: I think I could put my code in the core, but I don't _think_ I can just make it automatically enabled. * In sn65dsi I'd have to only enable it if we have a fixed refclk. * Maybe in ps8640 I could just always enable it and replace the existing code? I'd have to find someone to test. * In anx7625 things look totally different. Can you give me any advice on how you'd like me to proceed? -Doug
Hi, On Tue, Mar 16, 2021 at 5:44 PM Doug Anderson <dianders@chromium.org> wrote: > > Hi, > > On Tue, Mar 16, 2021 at 2:46 PM Laurent Pinchart > <laurent.pinchart@ideasonboard.com> wrote: > > > > Hi Doug, > > > > On Mon, Mar 15, 2021 at 09:25:37AM -0700, Doug Anderson wrote: > > > On Sat, Mar 13, 2021 at 1:17 PM Laurent Pinchart wrote: > > > > On Thu, Mar 04, 2021 at 03:52:01PM -0800, Douglas Anderson wrote: > > > > > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > > > > > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > > > > > EDID from the panel. That commit kinda worked but it had some serious > > > > > problems. > > > > > > > > > > The problems all stem from the fact that userspace wants to be able to > > > > > read the EDID before it explicitly enables the panel. For eDP panels, > > > > > though, we don't actually power the panel up until the pre-enable > > > > > stage and the pre-enable call happens right before the enable call > > > > > with no way to interject in-between. For eDP panels, you can't read > > > > > the EDID until you power the panel. The result was that > > > > > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > > > > > (falling back to what drm_panel_get_modes() returned) until _after_ > > > > > the EDID was needed. > > > > > > > > > > To make it concrete, on my system I saw this happen: > > > > > 1. We'd attach the bridge. > > > > > 2. Userspace would ask for the EDID (several times). We'd try but fail > > > > > to read the EDID over and over again and fall back to the hardcoded > > > > > modes. > > > > > 3. Userspace would decide on a mode based only on the hardcoded modes. > > > > > 4. Userspace would ask to turn the panel on. > > > > > 5. Userspace would (eventually) check the modes again (in Chrome OS > > > > > this happens on the handoff from the boot splash screen to the > > > > > browser). Now we'd read them properly and, if they were different, > > > > > userspace would request to change the mode. > > > > > > > > > > The fact that userspace would always end up using the hardcoded modes > > > > > at first significantly decreases the benefit of the EDID > > > > > reading. Also: if the modes were even a tiny bit different we'd end up > > > > > doing a wasteful modeset and at boot. > > > > > > > > s/and at/at/ ? > > > > > > Sure, I can correct if/when I respin or it can be corrected when landed. > > > > > > > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > > index 491c9c4f32d1..af3fb4657af6 100644 > > > > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > > @@ -16,6 +16,7 @@ > > > > > #include <linux/pm_runtime.h> > > > > > #include <linux/regmap.h> > > > > > #include <linux/regulator/consumer.h> > > > > > +#include <linux/workqueue.h> > > > > > > > > > > #include <asm/unaligned.h> > > > > > > > > > > @@ -130,6 +131,12 @@ > > > > > * @ln_assign: Value to program to the LN_ASSIGN register. > > > > > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > > > > > * > > > > > + * @pre_enabled_early: If true we did an early pre_enable at attach. > > > > > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > > > > > + * if a normal pre_enable never came. > > > > > > > > Could we simplify this by using the runtime PM autosuspend feature ? The > > > > configuration of the bridge would be moved from pre_enable to the PM > > > > runtime resume handler, the clk_disable_unprepare() call moved from > > > > post_disable to the runtime suspend handler, and the work queue replaced > > > > by usage of pm_runtime_put_autosuspend(). > > > > > > It's an interesting idea but I don't think I can make it work, at > > > least not in a generic enough way. Specifically we can also use this > > > bridge chip as a generic GPIO provider in Linux. When someone asks us > > > to read a GPIO then we have to power the bridge on > > > (pm_runtime_get_sync()) and when someone asks us to configure a GPIO > > > as an output then we actually leave the bridge powered until they stop > > > requesting it as an output. At the moment the only user of this > > > functionality (that I know of) is for the HPD pin on trogdor boards > > > (long story about why we don't use the dedicated HPD) but the API > > > supports using these GPIOs for anything and I've tested that it works. > > > It wouldn't be great to have to keep the panel on in order to access > > > the GPIOs. > > > > The issue you're trying to fix doesn't seem specific to this bridge, so > > handling it in the bridge driver bothers me :-S Is there any way we > > could handle this in the DRM core ? I don't want to see similar > > implementations duplicated in all HDMI/DP bridges. > > Yes, it is true that this problem could affect other drivers. ...and > in full disclosure I think there are other similar workarounds already > present. I haven't personally worked on those chips, but in > ps8640_bridge_get_edid() there is a somewhat similar workaround to > chain a pre-enable (though maybe it's not quite as optimized?). I'm > told that maybe something had to be handled for anx7625 (in > anx7625_get_edid()?) but that definitely doesn't look at all like it's > doing a pre-enable, so maybe things for that bridge just work > differently. > > One thing that makes me hesitant about trying to moving this to the > core is that even in sn65dsi86 there is a case where it won't work. As > I mentioned in the patch I'm not aware of anyone using it in > production, but if someone was using the MIPI clock as input to the > bridge chip instead of a fixed "refclk" then trying to get the EDID > after just "pre-enable" falls over. Said another way: I can say that > with this particular bridge chip, if you're using a fixed refclk, you > can read the EDID after the pre-enable. I don't know if that's always > true with all other bridge chips. > > So I guess in summary: I think I could put my code in the core, but I > don't _think_ I can just make it automatically enabled. > > * In sn65dsi I'd have to only enable it if we have a fixed refclk. > > * Maybe in ps8640 I could just always enable it and replace the > existing code? I'd have to find someone to test. > > * In anx7625 things look totally different. > > Can you give me any advice on how you'd like me to proceed? OK, I've got something that maybe looks better. You can tell me what you think [1]. I did manage to use PM Runtime to avoid some of the complexity and I put that usage in simple-panel. We'll see if I get yelled at for adding more to simple-panel. ;-P [1] https://lore.kernel.org/dri-devel/20210330025345.3980086-1-dianders@chromium.org/
Hi Doug, On Mon, Mar 29, 2021 at 07:57:05PM -0700, Doug Anderson wrote: > On Tue, Mar 16, 2021 at 5:44 PM Doug Anderson wrote: > > On Tue, Mar 16, 2021 at 2:46 PM Laurent Pinchart wrote: > > > On Mon, Mar 15, 2021 at 09:25:37AM -0700, Doug Anderson wrote: > > > > On Sat, Mar 13, 2021 at 1:17 PM Laurent Pinchart wrote: > > > > > On Thu, Mar 04, 2021 at 03:52:01PM -0800, Douglas Anderson wrote: > > > > > > In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over > > > > > > DDC") we attempted to make the ti-sn65dsi86 bridge properly read the > > > > > > EDID from the panel. That commit kinda worked but it had some serious > > > > > > problems. > > > > > > > > > > > > The problems all stem from the fact that userspace wants to be able to > > > > > > read the EDID before it explicitly enables the panel. For eDP panels, > > > > > > though, we don't actually power the panel up until the pre-enable > > > > > > stage and the pre-enable call happens right before the enable call > > > > > > with no way to interject in-between. For eDP panels, you can't read > > > > > > the EDID until you power the panel. The result was that > > > > > > ti_sn_bridge_connector_get_modes() was always failing to read the EDID > > > > > > (falling back to what drm_panel_get_modes() returned) until _after_ > > > > > > the EDID was needed. > > > > > > > > > > > > To make it concrete, on my system I saw this happen: > > > > > > 1. We'd attach the bridge. > > > > > > 2. Userspace would ask for the EDID (several times). We'd try but fail > > > > > > to read the EDID over and over again and fall back to the hardcoded > > > > > > modes. > > > > > > 3. Userspace would decide on a mode based only on the hardcoded modes. > > > > > > 4. Userspace would ask to turn the panel on. > > > > > > 5. Userspace would (eventually) check the modes again (in Chrome OS > > > > > > this happens on the handoff from the boot splash screen to the > > > > > > browser). Now we'd read them properly and, if they were different, > > > > > > userspace would request to change the mode. > > > > > > > > > > > > The fact that userspace would always end up using the hardcoded modes > > > > > > at first significantly decreases the benefit of the EDID > > > > > > reading. Also: if the modes were even a tiny bit different we'd end up > > > > > > doing a wasteful modeset and at boot. > > > > > > > > > > s/and at/at/ ? > > > > > > > > Sure, I can correct if/when I respin or it can be corrected when landed. > > > > > > > > > > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > > > index 491c9c4f32d1..af3fb4657af6 100644 > > > > > > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > > > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c > > > > > > @@ -16,6 +16,7 @@ > > > > > > #include <linux/pm_runtime.h> > > > > > > #include <linux/regmap.h> > > > > > > #include <linux/regulator/consumer.h> > > > > > > +#include <linux/workqueue.h> > > > > > > > > > > > > #include <asm/unaligned.h> > > > > > > > > > > > > @@ -130,6 +131,12 @@ > > > > > > * @ln_assign: Value to program to the LN_ASSIGN register. > > > > > > * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. > > > > > > * > > > > > > + * @pre_enabled_early: If true we did an early pre_enable at attach. > > > > > > + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach > > > > > > + * if a normal pre_enable never came. > > > > > > > > > > Could we simplify this by using the runtime PM autosuspend feature ? The > > > > > configuration of the bridge would be moved from pre_enable to the PM > > > > > runtime resume handler, the clk_disable_unprepare() call moved from > > > > > post_disable to the runtime suspend handler, and the work queue replaced > > > > > by usage of pm_runtime_put_autosuspend(). > > > > > > > > It's an interesting idea but I don't think I can make it work, at > > > > least not in a generic enough way. Specifically we can also use this > > > > bridge chip as a generic GPIO provider in Linux. When someone asks us > > > > to read a GPIO then we have to power the bridge on > > > > (pm_runtime_get_sync()) and when someone asks us to configure a GPIO > > > > as an output then we actually leave the bridge powered until they stop > > > > requesting it as an output. At the moment the only user of this > > > > functionality (that I know of) is for the HPD pin on trogdor boards > > > > (long story about why we don't use the dedicated HPD) but the API > > > > supports using these GPIOs for anything and I've tested that it works. > > > > It wouldn't be great to have to keep the panel on in order to access > > > > the GPIOs. > > > > > > The issue you're trying to fix doesn't seem specific to this bridge, so > > > handling it in the bridge driver bothers me :-S Is there any way we > > > could handle this in the DRM core ? I don't want to see similar > > > implementations duplicated in all HDMI/DP bridges. > > > > Yes, it is true that this problem could affect other drivers. ...and > > in full disclosure I think there are other similar workarounds already > > present. I haven't personally worked on those chips, but in > > ps8640_bridge_get_edid() there is a somewhat similar workaround to > > chain a pre-enable (though maybe it's not quite as optimized?). I'm > > told that maybe something had to be handled for anx7625 (in > > anx7625_get_edid()?) but that definitely doesn't look at all like it's > > doing a pre-enable, so maybe things for that bridge just work > > differently. > > > > One thing that makes me hesitant about trying to moving this to the > > core is that even in sn65dsi86 there is a case where it won't work. As > > I mentioned in the patch I'm not aware of anyone using it in > > production, but if someone was using the MIPI clock as input to the > > bridge chip instead of a fixed "refclk" then trying to get the EDID > > after just "pre-enable" falls over. Said another way: I can say that > > with this particular bridge chip, if you're using a fixed refclk, you > > can read the EDID after the pre-enable. I don't know if that's always > > true with all other bridge chips. > > > > So I guess in summary: I think I could put my code in the core, but I > > don't _think_ I can just make it automatically enabled. > > > > * In sn65dsi I'd have to only enable it if we have a fixed refclk. > > > > * Maybe in ps8640 I could just always enable it and replace the > > existing code? I'd have to find someone to test. > > > > * In anx7625 things look totally different. > > > > Can you give me any advice on how you'd like me to proceed? > > OK, I've got something that maybe looks better. You can tell me what > you think [1]. I did manage to use PM Runtime to avoid some of the > complexity and I put that usage in simple-panel. We'll see if I get > yelled at for adding more to simple-panel. ;-P > > [1] https://lore.kernel.org/dri-devel/20210330025345.3980086-1-dianders@chromium.org/ Nice :-) I'm unfortunately afraid I'm quite busy these days. Could you ping me in a few weeks if I haven't reviewed the series ?
diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c index 491c9c4f32d1..af3fb4657af6 100644 --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c @@ -16,6 +16,7 @@ #include <linux/pm_runtime.h> #include <linux/regmap.h> #include <linux/regulator/consumer.h> +#include <linux/workqueue.h> #include <asm/unaligned.h> @@ -130,6 +131,12 @@ * @ln_assign: Value to program to the LN_ASSIGN register. * @ln_polrs: Value for the 4-bit LN_POLRS field of SN_ENH_FRAME_REG. * + * @pre_enabled_early: If true we did an early pre_enable at attach. + * @pre_enable_timeout_work: Delayed work to undo the pre_enable from attach + * if a normal pre_enable never came. + * @pre_enable_mutex: Lock to synchronize between the pre_enable_timeout_work + * and normal mechanisms. + * * @gchip: If we expose our GPIOs, this is used. * @gchip_output: A cache of whether we've set GPIOs to output. This * serves double-duty of keeping track of the direction and @@ -158,6 +165,10 @@ struct ti_sn_bridge { u8 ln_assign; u8 ln_polrs; + bool pre_enabled_early; + struct delayed_work pre_enable_timeout_work; + struct mutex pre_enable_mutex; + #if defined(CONFIG_OF_GPIO) struct gpio_chip gchip; DECLARE_BITMAP(gchip_output, SN_NUM_GPIOS); @@ -272,12 +283,6 @@ static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector) struct edid *edid = pdata->edid; int num, ret; - if (!edid) { - pm_runtime_get_sync(pdata->dev); - edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc); - pm_runtime_put(pdata->dev); - } - if (edid && drm_edid_is_valid(edid)) { ret = drm_connector_update_edid_property(connector, edid); if (!ret) { @@ -412,10 +417,8 @@ static void ti_sn_bridge_post_disable(struct drm_bridge *bridge) pm_runtime_put_sync(pdata->dev); } -static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) +static void __ti_sn_bridge_pre_enable(struct ti_sn_bridge *pdata) { - struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); - pm_runtime_get_sync(pdata->dev); /* configure bridge ref_clk */ @@ -443,6 +446,38 @@ static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) drm_panel_prepare(pdata->panel); } +static void ti_sn_bridge_pre_enable(struct drm_bridge *bridge) +{ + struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); + + mutex_lock(&pdata->pre_enable_mutex); + if (pdata->pre_enabled_early) + /* Already done! Just mark that normal pre_enable happened */ + pdata->pre_enabled_early = false; + else + __ti_sn_bridge_pre_enable(pdata); + mutex_unlock(&pdata->pre_enable_mutex); +} + +static void ti_sn_bridge_cancel_early_pre_enable(struct ti_sn_bridge *pdata) +{ + mutex_lock(&pdata->pre_enable_mutex); + if (pdata->pre_enabled_early) { + pdata->pre_enabled_early = false; + ti_sn_bridge_post_disable(&pdata->bridge); + } + mutex_unlock(&pdata->pre_enable_mutex); +} + +static void ti_sn_bridge_pre_enable_timeout(struct work_struct *work) +{ + struct delayed_work *dwork = to_delayed_work(work); + struct ti_sn_bridge *pdata = container_of(dwork, struct ti_sn_bridge, + pre_enable_timeout_work); + + ti_sn_bridge_cancel_early_pre_enable(pdata); +} + static int ti_sn_bridge_attach(struct drm_bridge *bridge, enum drm_bridge_attach_flags flags) { @@ -516,6 +551,34 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge, } pdata->dsi = dsi; + /* + * If we have a refclk then we can support dynamic EDID. + * + * A few notes: + * - From trial and error it appears that we need our clock setup in + * order to read the EDID. If we don't have refclk then we + * (presumably) need the MIPI clock on, but turning that on implies + * knowing the pixel clock / not needing the EDID. Maybe we could + * futz this if necessary, but for now we won't. + * - In order to read the EDID we need power on to the bridge and + * the panel (and it has to finish booting up / assert HPD). This + * is slow so we leave the panel powered when we're done but setup a + * timeout so we don't leave it on forever. + * - The rest of Linux assumes that it can read the EDID without + * (explicitly) enabling the power which is why this somewhat awkward + * step is needed. + */ + if (pdata->refclk) { + mutex_lock(&pdata->pre_enable_mutex); + + pdata->pre_enabled_early = true; + __ti_sn_bridge_pre_enable(pdata); + pdata->edid = drm_get_edid(&pdata->connector, &pdata->aux.ddc); + schedule_delayed_work(&pdata->pre_enable_timeout_work, 30 * HZ); + + mutex_unlock(&pdata->pre_enable_mutex); + } + return 0; err_dsi_attach: @@ -525,6 +588,17 @@ static int ti_sn_bridge_attach(struct drm_bridge *bridge, return ret; } +static void ti_sn_bridge_detach(struct drm_bridge *bridge) +{ + struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); + + cancel_delayed_work_sync(&pdata->pre_enable_timeout_work); + ti_sn_bridge_cancel_early_pre_enable(pdata); + + kfree(pdata->edid); + pdata->edid = NULL; +} + static void ti_sn_bridge_disable(struct drm_bridge *bridge) { struct ti_sn_bridge *pdata = bridge_to_ti_sn_bridge(bridge); @@ -863,6 +937,7 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge) static const struct drm_bridge_funcs ti_sn_bridge_funcs = { .attach = ti_sn_bridge_attach, + .detach = ti_sn_bridge_detach, .pre_enable = ti_sn_bridge_pre_enable, .enable = ti_sn_bridge_enable, .disable = ti_sn_bridge_disable, @@ -1227,6 +1302,10 @@ static int ti_sn_bridge_probe(struct i2c_client *client, if (!pdata) return -ENOMEM; + mutex_init(&pdata->pre_enable_mutex); + INIT_DELAYED_WORK(&pdata->pre_enable_timeout_work, + ti_sn_bridge_pre_enable_timeout); + pdata->regmap = devm_regmap_init_i2c(client, &ti_sn_bridge_regmap_config); if (IS_ERR(pdata->regmap)) { @@ -1301,7 +1380,6 @@ static int ti_sn_bridge_remove(struct i2c_client *client) if (!pdata) return -EINVAL; - kfree(pdata->edid); ti_sn_debugfs_remove(pdata); of_node_put(pdata->host_node);
In commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC") we attempted to make the ti-sn65dsi86 bridge properly read the EDID from the panel. That commit kinda worked but it had some serious problems. The problems all stem from the fact that userspace wants to be able to read the EDID before it explicitly enables the panel. For eDP panels, though, we don't actually power the panel up until the pre-enable stage and the pre-enable call happens right before the enable call with no way to interject in-between. For eDP panels, you can't read the EDID until you power the panel. The result was that ti_sn_bridge_connector_get_modes() was always failing to read the EDID (falling back to what drm_panel_get_modes() returned) until _after_ the EDID was needed. To make it concrete, on my system I saw this happen: 1. We'd attach the bridge. 2. Userspace would ask for the EDID (several times). We'd try but fail to read the EDID over and over again and fall back to the hardcoded modes. 3. Userspace would decide on a mode based only on the hardcoded modes. 4. Userspace would ask to turn the panel on. 5. Userspace would (eventually) check the modes again (in Chrome OS this happens on the handoff from the boot splash screen to the browser). Now we'd read them properly and, if they were different, userspace would request to change the mode. The fact that userspace would always end up using the hardcoded modes at first significantly decreases the benefit of the EDID reading. Also: if the modes were even a tiny bit different we'd end up doing a wasteful modeset and at boot. As a side note: at least early EDID read failures were relatively fast. Though the old ti_sn_bridge_connector_get_modes() did call pm_runtime_get_sync() it didn't program the important "HPD_DISABLE" bit. That meant that all the AUX transfers failed pretty quickly. In any case, enough about the problem. How are we fixing it? Obviously we need to power the panel on _before_ reading the EDID, but how? It turns out that there's really no problem with just doing all the work of our pre_enable() function right at attach time and reading the EDID right away. We'll do that. It's not as easy as it sounds, though, because: 1. Powering the panel up and down is a pretty expensive operation. Not only do we need to wait for the HPD line which seems to take up to 200 ms on most panels, but also most panels say that once you power them off you need to wait at least 500 ms before powering them on again. We really don't want to incur 700 ms of time here. 2. If we happen not to have a fixed "refclk" we've got a chicken-and-egg problem. We seem to need the clock setup to read the EDID. Without a fixed "refclk", though, the bridge runs with the MIPI pixel clock which means you've got to use a hardcoded mode for the MIPI pixel clock. We'll solve problem #1 above by leaving the panel powered on for a little while after we read the EDID. If enough time passes and nobody turns the panel on then we'll undo our work. NOTE: there are no functional problems if someone turns the panel on after a long delay, it just might take a little longer to turn on. We'll solve problem #2 by simply _always_ using a hardcoded mode (not reading the EDID) if a "refclk" wasn't provided. While it might be possible to fudge something together to support this, it's my belief that nobody is using this mode in real life since it's really inflexible. I saw it used for some really early prototype hardware that was thrown in the e-waste bin years ago when we realized how inflexible it was. In any case, if someone is using this they're in no worse shape than they were before the (fairly recent) commit 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC"). NOTE: while this patch feels a bit hackish, I'm not sure there's much we can do better without a more fundamental DRM API change. After looking at it a bunch, it also doesn't feel as hacky to me as I first thought. The things that pre-enable does are well defined and well understood and there should be no problems with doing them early nor with doing them before userspace requests anything. Fixes: 58074b08c04a ("drm/bridge: ti-sn65dsi86: Read EDID blob over DDC") Signed-off-by: Douglas Anderson <dianders@chromium.org> --- drivers/gpu/drm/bridge/ti-sn65dsi86.c | 98 ++++++++++++++++++++++++--- 1 file changed, 88 insertions(+), 10 deletions(-)