Messages in this thread | | | Date | Wed, 27 Apr 2022 14:24:35 -0700 | Subject | Re: [PATCH 2/2] drm/probe-helper: For DP, add 640x480 if all other modes are bad | From | Kuogee Hsieh <> |
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Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
On 4/26/2022 2:17 PM, Doug Anderson wrote: > Hi, > > On Tue, Apr 26, 2022 at 2:11 PM Abhinav Kumar <quic_abhinavk@quicinc.com> wrote: >> >> >> On 4/26/2022 1:26 PM, Doug Anderson wrote: >>> Hi, >>> >>> On Tue, Apr 26, 2022 at 12:20 PM Abhinav Kumar >>> <quic_abhinavk@quicinc.com> wrote: >>>> Missed one more comment. >>>> >>>> On 4/26/2022 12:16 PM, Abhinav Kumar wrote: >>>>> Hi Doug >>>>> >>>>> One minor comment below. >>>>> >>>>> But otherwise, looking at this change this should work for us acc to me. >>>>> >>>>> We will test this out with our equipment and then provide R-b. >>>>> >>>>> Thanks >>>>> >>>>> Abhinav >>>>> On 4/26/2022 11:46 AM, Douglas Anderson 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> >>>>>> --- >>>>>> >>>>>> drivers/gpu/drm/drm_probe_helper.c | 26 +++++++++++++++++++++----- >>>>>> 1 file changed, 21 insertions(+), 5 deletions(-) >>>>>> >>>>>> diff --git a/drivers/gpu/drm/drm_probe_helper.c >>>>>> b/drivers/gpu/drm/drm_probe_helper.c >>>>>> index 819225629010..90cd46cbfec1 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); >>>>>> @@ -580,9 +579,26 @@ 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); >>>>>> + if (_drm_helper_update_and_validate(connector, maxX, maxY, >>>>>> &ctx)) { >>>>>> + drm_modeset_backoff(&ctx); >>>>>> + goto retry; >>>>> Do we need another retry here? This will again repeat everything from >>>>> get_modes(). >>>>> The fact that we are hitting this code is because we have already tried >>>>> that and this is already a second-pass. So I think another retry isnt >>>>> needed? >>>> This will help cover the case of 4.2.2.6 but not fix 4.2.2.1. >>>> >>>> For 4.2.2.1, we will have 0 modes and so the original DRM fwk code of >>>> adding all modes <= 1024x768 will kick in. >>>> >>>> Now, in that list, we will still need to pick/mark 640x480 as the >>>> preferred mode. >>>> >>>> We still need IGT for that. >>> Are you sure you don't have those backwards? It seems like 4.2.2.6 is >>> the test case dealing with corrupt EDID and that's the one that will >>> still be broken, no? ...and corrupt EDID is still the case where we >>> have 0 modes. >> Yes indeed, sorry, I did have the numbers backwards. >> 4.2.2.6 will still be broken. >> >>> In any case, let's see what people think about: >>> >>> https://lore.kernel.org/r/20220426132121.RFC.1.I31ec454f8d4ffce51a7708a8092f8a6f9c929092@changeid >> Yes sure. If it gets accepted, it will save us some IGT work. >> >>> I've marked that one as RFC just because it seems like a bigger change >>> to existing behavior, though it still seems correct to me. >>> >>> NOTE: reading 4.2.2.6 more closely, it actually looks as if we're >>> actually supposed to be able to try various video modes one at a time >>> until we find one that works (or land on 640x480). Seems as if we're >>> supposed to be able to try the higher resolutions one at a time and we >>> can tell whether the sink "accepted" it by seeing if SINK_STATUS goes >>> to 1? I have no idea how that works with all the Linux APIs, though. >>> >> hmmm .... our equipment throws a warning if we dont sent 640x480. So >> perhaps just go with the "or land on 640x480" option. >> >> 0006.392.232: [WARNING] Source DUT failed to transmit a video stream >> using fail-safe mode >> 0006.392.491: Received 1344 Htotal differs from fail-safe 800 >> 0006.392.621: Received 1024 Hactive differs from fail-safe 640 >> 0006.392.750: Received 296 Hstart differs from fail-safe 144 >> 0006.392.868: Received 136 Hsync width differs from fail-safe 96 >> 0006.392.975: Received 806 Vtotal differs from fail-safe 525 >> 0006.393.099: Received 768 Vactive differs from fail-safe 480 >> 0006.393.229: Received 6 Vsync width differs from fail-safe 2 > Do you actually have code to implement the checking of SINK_STATUS? > I'm not aware of how that would work in Linux, which is why just > defaulting to 640x480 seems like a reasonable thing to do for now. The > test case actually says that you're allowed to try clock rates one at > a time (polling SINK_STATUS in DPCT) as long as you don't spend more > than 5 seconds on each clock rate. According to the test case if you > never saw SINK_STATUS in DPCT go to 1 then you should end at 640x480.
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