Message ID | 20220511155749.v3.2.I4ac7f55aa446699f8c200a23c10463256f6f439f@changeid (mailing list archive) |
---|---|
State | Not Applicable |
Headers | show |
Series | [v3,1/2] drm/probe-helper: Add helper for drm_helper_probe_single_connector_modes() | expand |
Hi, On Wed, May 11, 2022 at 3:58 PM Douglas Anderson <dianders@chromium.org> wrote: > > As per Displayport spec section 5.2.1.2 ("Video Timing Format") says > that all detachable sinks shall support 640x480 @60Hz as a fail safe > mode. > > A DP compliance test expected us to utilize the above fact when all > modes it presented to the DP source were not achievable. It presented > only modes that would be achievable with more lanes and/or higher > speeds than we had available and expected that when we couldn't do > that then we'd fall back to 640x480 even though it didn't advertise > this size. > > In order to pass the compliance test (and also support any users who > might fall into a similar situation with their display), we need to > add 640x480 into the list of modes. However, we don't want to add > 640x480 all the time. Despite the fact that the DP spec says all sinks > _shall support_ 640x480, they're not guaranteed to support it > _well_. Continuing to read the spec you can see that the display is > not required to really treat 640x480 equal to all the other modes. It > doesn't need to scale or anything--just display the pixels somehow for > failsafe purposes. It should also be noted that it's not hard to find > a display hooked up via DisplayPort that _doesn't_ support 640x480 at > all. The HP ZR30w screen I'm sitting in front of has a native DP port > and doesn't work at 640x480. I also plugged in a tiny 800x480 HDMI > display via a DP to HDMI adapter and that screen definitely doesn't > support 640x480. > > As a compromise solution, let's only add the 640x480 mode if: > * We're on DP. > * All other modes have been pruned. > > This acknowledges that 640x480 might not be the best mode to use but, > since sinks are _supposed_ to support it, we will at least fall back > to it if there's nothing else. > > Note that we _don't_ add higher resolution modes like 1024x768 in this > case. We only add those modes for a failed EDID read where we have no > idea what's going on. In the case where we've pruned all modes then > instead we only want 640x480 which is the only defined "Fail Safe" > resolution. > > This patch originated in response to Kuogee Hsieh's patch [1]. > > [1] https://lore.kernel.org/r/1650671124-14030-1-git-send-email-quic_khsieh@quicinc.com > > Signed-off-by: Douglas Anderson <dianders@chromium.org> > Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com> > Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com> > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> > --- > > Changes in v3: > - Removed WARN_ON > > Changes in v2: > - Two underscores for __drm_helper_update_and_validate(). > - Return err and use WARN_ON instead of returning a bool. > > drivers/gpu/drm/drm_probe_helper.c | 27 ++++++++++++++++++++++----- > 1 file changed, 22 insertions(+), 5 deletions(-) Pushed to drm-misc-next: e7c254d75d16 drm/probe-helper: For DP, add 640x480 if all other modes are bad
diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 2570d47e7eab..6fe28bc6595d 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -476,7 +476,6 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector, const struct drm_connector_helper_funcs *connector_funcs = connector->helper_private; int count = 0, ret; - bool verbose_prune = true; enum drm_connector_status old_status; struct drm_modeset_acquire_ctx ctx; @@ -556,8 +555,8 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector, DRM_DEBUG_KMS("[CONNECTOR:%d:%s] disconnected\n", connector->base.id, connector->name); drm_connector_update_edid_property(connector, NULL); - verbose_prune = false; - goto prune; + drm_mode_prune_invalid(dev, &connector->modes, false); + goto exit; } count = (*connector_funcs->get_modes)(connector); @@ -581,9 +580,27 @@ int drm_helper_probe_single_connector_modes(struct drm_connector *connector, } } -prune: - drm_mode_prune_invalid(dev, &connector->modes, verbose_prune); + drm_mode_prune_invalid(dev, &connector->modes, true); + /* + * Displayport spec section 5.2.1.2 ("Video Timing Format") says that + * all detachable sinks shall support 640x480 @60Hz as a fail safe + * mode. If all modes were pruned, perhaps because they need more + * lanes or a higher pixel clock than available, at least try to add + * in 640x480. + */ + if (list_empty(&connector->modes) && + connector->connector_type == DRM_MODE_CONNECTOR_DisplayPort) { + count = drm_add_modes_noedid(connector, 640, 480); + ret = __drm_helper_update_and_validate(connector, maxX, maxY, &ctx); + if (ret == -EDEADLK) { + drm_modeset_backoff(&ctx); + goto retry; + } + drm_mode_prune_invalid(dev, &connector->modes, true); + } + +exit: drm_modeset_drop_locks(&ctx); drm_modeset_acquire_fini(&ctx);