Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <537e8e8b-03f7-9fc0-4416-3b69d375ba9b@quicinc.com>
Date:   Wed, 29 Jun 2022 19:10:21 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.6.2
Subject: Re: [Freedreno] [PATCH] drm/msm/dp: make eDP panel as the first
 connected connector
Content-Language: en-US
To:     Rob Clark <robdclark@gmail.com>,
        Doug Anderson <dianders@chromium.org>
CC:     freedreno <freedreno@lists.freedesktop.org>,
        Sankeerth Billakanti <quic_sbillaka@quicinc.com>,
        David Airlie <airlied@linux.ie>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@quicinc.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Stephen Boyd <swboyd@chromium.org>,
        "Vinod Koul" <vkoul@kernel.org>, Andy Gross <agross@kernel.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        "Dmitry Baryshkov" <dmitry.baryshkov@linaro.org>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@quicinc.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Sean Paul <sean@poorly.run>,
        LKML <linux-kernel@vger.kernel.org>
References: <1656429606-2765-1-git-send-email-quic_khsieh@quicinc.com>
 <F35C87BF-46A5-41D3-B8A5-B2AB4A24252D@linaro.org>
 <CAD=FV=X3cv=Q30pODyi__OyRY+LbFT14RfEELvm_DAeHafF70g@mail.gmail.com>
 <CAF6AEGvFYK3x_CmErkKsmYNEv9y8AksE9UB_sfp-Z7RieX=tVg@mail.gmail.com>
From:   Abhinav Kumar <quic_abhinavk@quicinc.com>
In-Reply-To: <CAF6AEGvFYK3x_CmErkKsmYNEv9y8AksE9UB_sfp-Z7RieX=tVg@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 6/29/2022 6:57 PM, Rob Clark wrote:
> On Wed, Jun 29, 2022 at 5:36 PM Doug Anderson <dianders@chromium.org> wrote:
>>
>> Hi,
>>
>> On Tue, Jun 28, 2022 at 1:14 PM Dmitry Baryshkov
>> <dmitry.baryshkov@linaro.org> wrote:
>>>
>>> On 28 June 2022 18:20:06 GMT+03:00, Kuogee Hsieh <quic_khsieh@quicinc.com> wrote:
>>>> Some userspace presumes that the first connected connector is the main
>>>> display, where it's supposed to display e.g. the login screen. For
>>>> laptops, this should be the main panel.
>>>>
>>>> This patch call drm_helper_move_panel_connectors_to_head() after
>>>> drm_bridge_connector_init() to make sure eDP stay at head of
>>>> connected connector list. This fixes unexpected corruption happen
>>>> at eDP panel if eDP is not placed at head of connected connector
>>>> list.
>>>
>>> The change itself is a good fix anyway. (And I'd ack it.) However I would like to understand why does it fix the corruption issue. What is we have eDP and DSI, with DSI ending up before the eDP? Would we see the issue?
>>> Also could you please describe the mind of corruption you are observing?
>>
>> I've spent a whole bunch of time poking at this and in the end my
>> conclusion is this:
>>
>> 1. The glitchyness seems to be a result of the Chrome OS userspace
>> somehow telling the kernel to do something wrong.
>>
>> 2. I believe (though I have no proof other than Kuogee's patch fixing
>> things) that the Chrome OS userspace is simply confused by the eDP
>> connector being second. This would imply that Kuogee's patch is
>> actually the right one.
>>
>> 3. It would be ideal if the Chrome OS userspace were fixed to handle
>> this, but it's an area of code that I've never looked at. It also
>> seems terribly low priority to fix since apparently other OSes have
>> similar problems (seems like this code was originally added by
>> RedHat?)
>>
>>
>> Specifically, I tested with a similar but "persistent" glitch that I
>> reproduced. The glitch Kuogee was digging into was a transitory glitch
>> on the eDP (internal) display when you plugged in a DP (external)
>> display. It would show up for a frame or two and then be fixed. I can
>> get a similar-looking glitch (vertical black and white bars) that
>> persists by doing these steps on a Chrome OS device (and Chrome OS
>> kernel):
>>
>> a) Observe screen looks good.
>> b) Observe DP not connected.
>> c) Plug in DP
>> d) See transitory glitch on screen, then it all looks fine.
>> e) set_power_policy --ac_screen_dim_delay=5 --ac_screen_off_delay=10
>> f) Wait for screen to turn off
>> g) Unplug DP
>> h) Hit key on keyboard to wake device.
>> i) See glitchy.
>> j) Within 5 seconds: set_power_policy --ac_screen_dim_delay=5000
>> --ac_screen_off_delay=10000
>>
>> Once I'm in the persistent glitch:
>>
>> * The "screenshot" command in Chrome OS shows corruption. Not exactly
>> black and white bars, but the image produced has distinct bands of
>> garbage.
>>
>> * I can actually toggle between VT2 and the main screen (VT1). Note
>> that VT1/VT2 are not quite the normal Linux managed solution--I
>> believe they're handled by frecon. In any case, when I switch to VT2
>> it looks normal (I can see the login prompt). Then back to VT1 and the
>> vertical bars glitch. Back to VT2 and it's normal. Back to VT1 and the
>> glitch again. This implies (especially with the extra evidence of
>> screenshot) that the display controller hardware is all fine and that
>> it's the underlying data that's somehow messed up.
> 
> fwiw, from looking at this a bit w/ Doug, I think the "glitch" is
> simply just an un-renderered buffer being interpreted by the display
> controller as UBWC (because userspace tells it to)
> 
> BR,
> -R

Acked and agree with the comments both of you have stated and looking at 
the corrupted buffers in the snapshot.

Hence,

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>

> 
>> When I pick Kuogee's patch then this "persistent" glitch goes away
>> just like the transitory one does.
>>
>> I'm going to go ahead and do:
>>
>> Reviewed-by: Douglas Anderson <dianders@chromium.org>
>> Tested-by: Douglas Anderson <dianders@chromium.org>