linux-kernel - Re: Re: Re:[PATCH] drm/panel-edp: Add BOE NV140FHM-N4Z panel entry

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Message-ID: <CAD=FV=XU6Jij=ddAcq3F=VjP=Ls6DxSQ8VY6o+QHXHmagAkUFg@mail.gmail.com>
Date: Wed, 15 Jan 2025 09:40:20 -0800
From: Doug Anderson <dianders@...omium.org>
To: Andy Yan <andyshrk@....com>
Cc: quic_jesszhan@...cinc.com, maarten.lankhorst@...ux.intel.com, 
	mripard@...nel.org, neil.armstrong@...aro.org, tzimmermann@...e.de, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: Re: Re:[PATCH] drm/panel-edp: Add BOE NV140FHM-N4Z panel entry

Hi,

On Wed, Jan 15, 2025 at 1:45 AM Andy Yan <andyshrk@....com> wrote:
>
>
> Hi Doug,
>
> 在 2025-01-15 00:44:41，"Doug Anderson" <dianders@...omium.org> 写道：
> >Hi,
> >
> >On Tue, Jan 14, 2025 at 1:05 AM Andy Yan <andyshrk@....com> wrote:
> >>
> >>
> >> Hi All,
> >>
> >> At 2025-01-13 18:17:38, "Andy Yan" <andyshrk@....com> wrote:
> >> >
> >> >Sorry, please don't merge this patch. after further testing,
> >> >I found that there are still some changce, it can't read edid.
> >>
> >> It turns out that we need set hpd-reliable-delay-ms = 120 in dts to ensure
> >> the right time to access edid.
> >
> >That seems awfully high and feels likely to be a problem with your
> >board design and not the panel. Are you sure HPD is even hooked up
> >properly on your board? Maybe you're missing a pullup/pulldown config
> >somewhere? Would it be better to just specify "no-hpd" and get the
> >full "HPD absent" delay?
> >
>
> Yes, you are right, after checking the schematic, I found that the HDP indeed does not
> hooked up on the board.
>
> I do more tests with hpd-reliable-delay-ms to a short value, From the current tests, this
> value can be set below 10, even lower, but I need to do more tests to confirm how low
> it can actually be set。

If HPD isn't hooked up on your board then I would suggest using the
"no-hpd" + "hpd-absent-delay-ms" instead of "hpd-reliable-delay-ms".
That more accurately describes your hardware. I'd personally pick "200
ms" for your "hpd-absent-delay-ms" unless you know for sure that all
the panels you might hook up have less or more. 200 ms is very common
for the max HPD time.

-Doug