| Message ID | 20241211-drm-dp-msm-add-lttpr-transparent-mode-set-v2-1-d5906ed38b28@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/dp: Rework LTTPR transparent mode handling and add support to msm driver | expand |
On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > +/** > + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode > + * @aux: DisplayPort AUX channel > + * @enable: Enable or disable transparent mode > + * > + * Returns 0 on success or a negative error code on failure. > + */ > +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) > +{ > + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : > + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; > + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); > + > + return ret == 1 ? 0 : ret; This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make sure it never returns 0 (for short transfers). > +} > +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); This appears to be what the driver currently uses, but why not EXPORT_SYMBOL_GPL? > + > +/** > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard > + * > + * @aux: DisplayPort AUX channel > + * @lttpr_count: Number of LTTPRs > + * > + * Returns 0 on success or a negative error code on failure. > + */ > +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count) > +{ > + if (!lttpr_count) > + return 0; > + > + /* > + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of > + * non-transparent mode and the disable->enable non-transparent mode > + * sequence. > + */ > + drm_dp_lttpr_set_transparent_mode(aux, true); Error handling? > + > + if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false)) No need to check lttpr_count again here. > + return 0; I'd check for errors instead of success here and do the rollback before returning -EINVAL. > + > + /* > + * Roll-back to tranparent mode if setting non-tranparent mode failed or > + * the number of LTTPRs is invalid > + */ > + drm_dp_lttpr_set_transparent_mode(aux, true); > + > + return -EINVAL; And return 0 explicitly here. > +} > +EXPORT_SYMBOL(drm_dp_lttpr_init); In any case this works well and is needed for external display on the Lenovo ThinkPad T14s, while not breaking the X13s which does not need it: Tested-by: Johan Hovold <johan+linaro@kernel.org> Johan
On Wed, Dec 11, 2024 at 03:42:27PM +0100, Johan Hovold wrote: > On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > > > +/** > > + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode > > + * @aux: DisplayPort AUX channel > > + * @enable: Enable or disable transparent mode > > + * > > + * Returns 0 on success or a negative error code on failure. > > + */ > > +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) > > +{ > > + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : > > + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; > > + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); > > + > > + return ret == 1 ? 0 : ret; > > This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make > sure it never returns 0 (for short transfers). > > > +} > > +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); > > This appears to be what the driver currently uses, but why not > EXPORT_SYMBOL_GPL? $ git grep EXPORT_SYMBOL drivers/gpu/drm/*.c | wc -l 962 $ git grep EXPORT_SYMBOL_GPL drivers/gpu/drm/*.c | wc -l 93
On Wed, Dec 11, 2024 at 03:42:27PM +0100, Johan Hovold wrote: > On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > > > +/** > > + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode > > + * @aux: DisplayPort AUX channel > > + * @enable: Enable or disable transparent mode > > + * > > + * Returns 0 on success or a negative error code on failure. > > + */ > > +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) > > +{ > > + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : > > + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; > > + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); > > + > > + return ret == 1 ? 0 : ret; > > This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make > sure it never returns 0 (for short transfers). Indeed. It got me a while to check that drm_dp_dpcd_writeb() -> drm_dp_mst_dpcd_write() -> drm_dp_send_dpcd_write() -> drm_dp_mst_wait_tx_reply() never returns '0'. I'd prefer an explicit if (ret < 0) return ret; return (ret == 1) ? 0 : -EIO; > > > +} > > +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); >
On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > According to the DisplayPort standard, LTTPRs have two operating > modes: > - non-transparent - it replies to DPCD LTTPR field specific AUX > requests, while passes through all other AUX requests > - transparent - it passes through all AUX requests. > > Switching between this two modes is done by the DPTX by issuing > an AUX write to the DPCD PHY_REPEATER_MODE register. > > Add a generic helper that allows switching between these modes. > > Also add a generic wrapper for the helper that handles the explicit > disabling of non-transparent mode and its disable->enable sequence > mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order > to move this handling out of the vendor specific driver implementation > into the generic framework. > > Signed-off-by: Abel Vesa <abel.vesa@linaro.org> > --- > drivers/gpu/drm/display/drm_dp_helper.c | 50 +++++++++++++++++++++++++++++++++ > include/drm/display/drm_dp_helper.h | 2 ++ > 2 files changed, 52 insertions(+) > > +/** > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard > + * > + * @aux: DisplayPort AUX channel > + * @lttpr_count: Number of LTTPRs > + * > + * Returns 0 on success or a negative error code on failure. > + */ > +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count) > +{ > + if (!lttpr_count) > + return 0; > + > + /* > + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of > + * non-transparent mode and the disable->enable non-transparent mode > + * sequence. > + */ > + drm_dp_lttpr_set_transparent_mode(aux, true); > + > + if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false)) > + return 0; > + > + /* > + * Roll-back to tranparent mode if setting non-tranparent mode failed or > + * the number of LTTPRs is invalid > + */ > + drm_dp_lttpr_set_transparent_mode(aux, true); This means that if lttpr_count < 0, then there will be two requests to set LTTPRs to a transparent mode. Is that expected? > + > + return -EINVAL; > +} > +EXPORT_SYMBOL(drm_dp_lttpr_init); > +
On Wed, 11 Dec 2024, Dmitry Baryshkov <dmitry.baryshkov@linaro.org> wrote: > On Wed, Dec 11, 2024 at 03:42:27PM +0100, Johan Hovold wrote: >> On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: >> >> > +/** >> > + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode >> > + * @aux: DisplayPort AUX channel >> > + * @enable: Enable or disable transparent mode >> > + * >> > + * Returns 0 on success or a negative error code on failure. >> > + */ >> > +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) >> > +{ >> > + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : >> > + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; >> > + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); >> > + >> > + return ret == 1 ? 0 : ret; >> >> This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make >> sure it never returns 0 (for short transfers). >> >> > +} >> > +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); >> >> This appears to be what the driver currently uses, but why not >> EXPORT_SYMBOL_GPL? > > $ git grep EXPORT_SYMBOL drivers/gpu/drm/*.c | wc -l > 962 > $ git grep EXPORT_SYMBOL_GPL drivers/gpu/drm/*.c | wc -l > 93 It's even more tilted under display/. BR, Jani.
On 11/12/2024 15:42, Johan Hovold wrote: > On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > >> +/** >> + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode >> + * @aux: DisplayPort AUX channel >> + * @enable: Enable or disable transparent mode >> + * >> + * Returns 0 on success or a negative error code on failure. >> + */ >> +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) >> +{ >> + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : >> + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; >> + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); >> + >> + return ret == 1 ? 0 : ret; > > This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make > sure it never returns 0 (for short transfers). > >> +} >> +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); > > This appears to be what the driver currently uses, but why not > EXPORT_SYMBOL_GPL? drivers/gpu/drm/display/drm_dp_helper.c is not GPL licenced, so this is the right macro to use. Neil > >> + >> +/** >> + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard >> + * >> + * @aux: DisplayPort AUX channel >> + * @lttpr_count: Number of LTTPRs >> + * >> + * Returns 0 on success or a negative error code on failure. >> + */ >> +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count) >> +{ >> + if (!lttpr_count) >> + return 0; >> + >> + /* >> + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of >> + * non-transparent mode and the disable->enable non-transparent mode >> + * sequence. >> + */ >> + drm_dp_lttpr_set_transparent_mode(aux, true); > > Error handling? > >> + >> + if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false)) > > No need to check lttpr_count again here. > >> + return 0; > > I'd check for errors instead of success here and do the rollback before > returning -EINVAL. > >> + >> + /* >> + * Roll-back to tranparent mode if setting non-tranparent mode failed or >> + * the number of LTTPRs is invalid >> + */ >> + drm_dp_lttpr_set_transparent_mode(aux, true); >> + >> + return -EINVAL; > > And return 0 explicitly here. > >> +} >> +EXPORT_SYMBOL(drm_dp_lttpr_init); > > In any case this works well and is needed for external display on the > Lenovo ThinkPad T14s, while not breaking the X13s which does not need > it: > > Tested-by: Johan Hovold <johan+linaro@kernel.org> > > Johan >
On Thu, Dec 12, 2024 at 09:31:09AM +0100, neil.armstrong@linaro.org wrote: > On 11/12/2024 15:42, Johan Hovold wrote: > >> +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); > > > > This appears to be what the driver currently uses, but why not > > EXPORT_SYMBOL_GPL? > > drivers/gpu/drm/display/drm_dp_helper.c is not GPL licenced, so > this is the right macro to use. Wow. I should have checked the header. Thanks for explaining. Johan
On 24-12-11 21:22:00, Dmitry Baryshkov wrote: > On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > > According to the DisplayPort standard, LTTPRs have two operating > > modes: > > - non-transparent - it replies to DPCD LTTPR field specific AUX > > requests, while passes through all other AUX requests > > - transparent - it passes through all AUX requests. > > > > Switching between this two modes is done by the DPTX by issuing > > an AUX write to the DPCD PHY_REPEATER_MODE register. > > > > Add a generic helper that allows switching between these modes. > > > > Also add a generic wrapper for the helper that handles the explicit > > disabling of non-transparent mode and its disable->enable sequence > > mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order > > to move this handling out of the vendor specific driver implementation > > into the generic framework. > > > > Signed-off-by: Abel Vesa <abel.vesa@linaro.org> > > --- > > drivers/gpu/drm/display/drm_dp_helper.c | 50 +++++++++++++++++++++++++++++++++ > > include/drm/display/drm_dp_helper.h | 2 ++ > > 2 files changed, 52 insertions(+) > > > > > > +/** > > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard > > + * > > + * @aux: DisplayPort AUX channel > > + * @lttpr_count: Number of LTTPRs > > + * > > + * Returns 0 on success or a negative error code on failure. > > + */ > > +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count) > > +{ > > + if (!lttpr_count) > > + return 0; > > + > > + /* > > + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of > > + * non-transparent mode and the disable->enable non-transparent mode > > + * sequence. > > + */ > > + drm_dp_lttpr_set_transparent_mode(aux, true); > > + > > + if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false)) > > + return 0; > > + > > + /* > > + * Roll-back to tranparent mode if setting non-tranparent mode failed or > > + * the number of LTTPRs is invalid > > + */ > > + drm_dp_lttpr_set_transparent_mode(aux, true); > > This means that if lttpr_count < 0, then there will be two requests to > set LTTPRs to a transparent mode. Is that expected? Yes, exactly. If counting the LTTPRs (see drm_dp_lttpr_count) results in an invalid number (e.g. more than 8), then according to the DP standard, we need to roll back to transparent mode. Do you think I need to re-word the comment above more to make it more clearer? > > > + > > + return -EINVAL; > > +} > > +EXPORT_SYMBOL(drm_dp_lttpr_init); > > + > > -- > With best wishes > Dmitry Thanks for reviewing, Abel
On 24-12-11 15:42:27, Johan Hovold wrote: > On Wed, Dec 11, 2024 at 03:04:12PM +0200, Abel Vesa wrote: > > > +/** > > + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode > > + * @aux: DisplayPort AUX channel > > + * @enable: Enable or disable transparent mode > > + * > > + * Returns 0 on success or a negative error code on failure. > > + */ > > +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) > > +{ > > + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : > > + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; > > + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); > > + > > + return ret == 1 ? 0 : ret; > > This looks correct, but I had to go look at drm_dp_dpcd_writeb() to make > sure it never returns 0 (for short transfers). Will follow Dmitry's proposal here. if (ret < 0) return ret; return (ret == 1) ? 0 : -EIO; > > > +} > > +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); > > This appears to be what the driver currently uses, but why not > EXPORT_SYMBOL_GPL? > > > + > > +/** > > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard > > + * > > + * @aux: DisplayPort AUX channel > > + * @lttpr_count: Number of LTTPRs > > + * > > + * Returns 0 on success or a negative error code on failure. > > + */ > > +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count) > > +{ > > + if (!lttpr_count) > > + return 0; > > + > > + /* > > + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of > > + * non-transparent mode and the disable->enable non-transparent mode > > + * sequence. > > + */ > > + drm_dp_lttpr_set_transparent_mode(aux, true); > > Error handling? Yes, this makes sense. But other than throwing an error I don't think there is much to be done. I'll add an drm_err here just in case. > > > + > > + if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false)) > > No need to check lttpr_count again here. So the logic behind lttpr_count and this transparency mode changing, as specified in the DP standard, is as follows: - If there are 0 LTTPRs counted, then nothing to be done, otherwise set to transparent mode. - Then, if there are between 0 and 8 LTTPRs counted, set non-transparent mode successfully. - Otherwise, rollback to transparent mode. This last rollback might result in two transparent mode settings without a non-transparent one in between, but AFAIU, that is OK. Making sure this doesn't happen would just make the implementation more ugly without any benefit, IMO. > > > + return 0; > > I'd check for errors instead of success here and do the rollback before > returning -EINVAL. > Yes, I think it would be more cleaner. Will do that. > > + > > + /* > > + * Roll-back to tranparent mode if setting non-tranparent mode failed or > > + * the number of LTTPRs is invalid > > + */ > > + drm_dp_lttpr_set_transparent_mode(aux, true); > > + > > + return -EINVAL; > > And return 0 explicitly here. Yes. Will do that. > > > +} > > +EXPORT_SYMBOL(drm_dp_lttpr_init); > > In any case this works well and is needed for external display on the > Lenovo ThinkPad T14s, while not breaking the X13s which does not need > it: > > Tested-by: Johan Hovold <johan+linaro@kernel.org> > > Johan Thanks for reviewing and testing! Abel
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..6abc54cd28e93d8101358ce05be51d4516778451 100644 --- a/drivers/gpu/drm/display/drm_dp_helper.c +++ b/drivers/gpu/drm/display/drm_dp_helper.c @@ -2817,6 +2817,56 @@ int drm_dp_lttpr_max_link_rate(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]) } EXPORT_SYMBOL(drm_dp_lttpr_max_link_rate); +/** + * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode + * @aux: DisplayPort AUX channel + * @enable: Enable or disable transparent mode + * + * Returns 0 on success or a negative error code on failure. + */ +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable) +{ + u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT : + DP_PHY_REPEATER_MODE_NON_TRANSPARENT; + int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val); + + return ret == 1 ? 0 : ret; +} +EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode); + +/** + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard + * + * @aux: DisplayPort AUX channel + * @lttpr_count: Number of LTTPRs + * + * Returns 0 on success or a negative error code on failure. + */ +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count) +{ + if (!lttpr_count) + return 0; + + /* + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of + * non-transparent mode and the disable->enable non-transparent mode + * sequence. + */ + drm_dp_lttpr_set_transparent_mode(aux, true); + + if (lttpr_count > 0 && !drm_dp_lttpr_set_transparent_mode(aux, false)) + return 0; + + /* + * Roll-back to tranparent mode if setting non-tranparent mode failed or + * the number of LTTPRs is invalid + */ + drm_dp_lttpr_set_transparent_mode(aux, true); + + return -EINVAL; +} +EXPORT_SYMBOL(drm_dp_lttpr_init); + /** * drm_dp_lttpr_max_lane_count - get the maximum lane count supported by all LTTPRs * @caps: LTTPR common capabilities diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h index 8f4054a560396a43750570a8c2e95624039ab8ad..3311df3b58255cf0620391d0948ccf6b569a8a34 100644 --- a/include/drm/display/drm_dp_helper.h +++ b/include/drm/display/drm_dp_helper.h @@ -630,6 +630,8 @@ int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux, u8 caps[DP_LTTPR_PHY_CAP_SIZE]); int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]); int drm_dp_lttpr_max_link_rate(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]); +int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable); +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count); int drm_dp_lttpr_max_lane_count(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]); bool drm_dp_lttpr_voltage_swing_level_3_supported(const u8 caps[DP_LTTPR_PHY_CAP_SIZE]); bool drm_dp_lttpr_pre_emphasis_level_3_supported(const u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
According to the DisplayPort standard, LTTPRs have two operating modes: - non-transparent - it replies to DPCD LTTPR field specific AUX requests, while passes through all other AUX requests - transparent - it passes through all AUX requests. Switching between this two modes is done by the DPTX by issuing an AUX write to the DPCD PHY_REPEATER_MODE register. Add a generic helper that allows switching between these modes. Also add a generic wrapper for the helper that handles the explicit disabling of non-transparent mode and its disable->enable sequence mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order to move this handling out of the vendor specific driver implementation into the generic framework. Signed-off-by: Abel Vesa <abel.vesa@linaro.org> --- drivers/gpu/drm/display/drm_dp_helper.c | 50 +++++++++++++++++++++++++++++++++ include/drm/display/drm_dp_helper.h | 2 ++ 2 files changed, 52 insertions(+)