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From:   Stephen Boyd <swboyd@chromium.org>
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Date:   Mon, 24 Jan 2022 14:07:23 -0800
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Subject: Re: [PATCH] drm/msm/dp: always add fail-safe mode into connector mode list
To:     Kuogee Hsieh <quic_khsieh@quicinc.com>, agross@kernel.org,
        airlied@linux.ie, bjorn.andersson@linaro.org, daniel@ffwll.ch,
        dmitry.baryshkov@linaro.org, robdclark@gmail.com, sean@poorly.run,
        vkoul@kernel.org
Cc:     quic_abhinavk@quicinc.com, aravindh@codeaurora.org,
        freedreno@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
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Quoting Kuogee Hsieh (2022-01-24 13:24:25)
>
> On 1/24/2022 1:04 PM, Stephen Boyd wrote:
> > Quoting Kuogee Hsieh (2022-01-24 12:46:10)
> >> Some of DP link compliant test expects to return fail-safe mode
> >> if prefer detailed timing mode can not be supported by mainlink's
> >> lane and rate after link training. Therefore add fail-safe mode
> >> into connector mode list as backup mode. This patch fixes test
> >> case 4.2.2.1.
> >>
> >> Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
> > Any Fixes tag? I also wonder why this isn't pushed into the DP core code
> > somehow. Wouldn't every device need to add a 640x480 mode by default?
>
> Original test case 4.2.2.1 always passed until we did firmware upgrade
> of our compliance test tester (Unigraph) recently.

Ok. So the Fixes tag should be the introduction of the driver or at
least whenever compliance testing support was added.

>
> The new firmware of tester use newer edid contains 1080p with 145.7 mhz
> which can not be supported by 2 lanes with 1.6G rate. Hence we failed
> this test case.

Interesting. So the test case wouldn't fail unless the number of lanes
were limited by the hardware? Seems that the test isn't thorough.

>
> After discuss with Vendor, they claims we have to return fail-safe mode
> if prefer detailed timing mode can not be supported.
>
> I think would be good to add fail-safe mode into connector mode list.
>
>
>
>
> > we just run into this problem recently.


Sure I'm not saying it's incorrect, just wondering why a connector
that's DP wouldn't have the 640x480 resolution by default somewhere in
the drm core.