linux-kernel - Re: [PATCH] drm/panel: boe-tv101wum-nl6: Fine tune Himax83102-j02 panel HFP and HBP

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Message-ID: <CAD=FV=UvZ9U1SYjOOBB6o2CmquAevqJZ9Ukp_kx4zGXFbp_VBA@mail.gmail.com>
Date:   Fri, 10 Nov 2023 13:09:46 -0800
From:   Doug Anderson <dianders@...gle.com>
To:     Cong Yang <yangcong5@...qin.corp-partner.google.com>
Cc:     sam@...nborg.org, neil.armstrong@...aro.org, daniel@...ll.ch,
        hsinyi@...gle.com, airlied@...il.com, zhouruihai@...qin.com,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: boe-tv101wum-nl6: Fine tune Himax83102-j02
 panel HFP and HBP

Hi,

On Fri, Nov 10, 2023 at 1:46 AM Cong Yang
<yangcong5@...qin.corp-partner.google.com> wrote:
>
> The refresh reported by modotest is 60.46Hz, and the actual measurement

s/modotets/modetest/

> is 60.01Hz, which is outside the expected tolerance. Adjust hporch and
> pixel clock to fix it. After repair, modetest and actual measurement were
> all 60.01Hz.

Can you explain this more? Why was the rate that modetest reported
different from the actual measured rate? This feels like it's a
problem with your MIPI controller not being able to accurately make
the rate. Is that it?

If so then this is a bit of a hack. Someone else using the same panel
might have a MIPI controller that can make slightly different clock
rates. I think you're currently the only user of the panel, so maybe
this isn't too terrible (would love to hear other people's advice).

Assuming this is actually the problem there are probably at least
several different ways to solve this. One that comes to mind is the
solution we ended up with for eDP where we allowed specifying some of
this stuff in the device tree, though that might cause a whole pile of
debates...

In any case, as I said above this patch is probably OK if you're the
only user of this panel, but it might be at least good to add
something to the commit message?

-Doug