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From:   Doug Anderson <dianders@chromium.org>
Date:   Fri, 7 Apr 2023 10:06:33 -0700
Message-ID: <CAD=FV=VR7sKsquE25eF7joc7gPApu-vqwduZzjE=wFCoXjMYnQ@mail.gmail.com>
Subject: Re: [PATCH v5 4/4] arm64: dts: qcom: Add Acer Aspire 1
To:     Nikita Travkin <nikita@trvn.ru>
Cc:     agross@kernel.org, andersson@kernel.org, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org, konrad.dybcio@linaro.org,
        quic_srivasam@quicinc.com, judyhsiao@chromium.org,
        mka@chromium.org, cros-qcom-dts-watchers@chromium.org,
        linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, ~postmarketos/upstreaming@lists.sr.ht
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Hi,

On Fri, Apr 7, 2023 at 9:46=E2=80=AFAM Nikita Travkin <nikita@trvn.ru> wrot=
e:
>
> > HPD might very well be hooked up on your board, but the current Linux
> > ti-sn65dsi86 driver does not look at its own HPD line because it's
> > actually slower than just pretending that HPD isn't there. On trogdor
> > boards we ended up routing HPD to a GPIO.
> >
>
> Oh, this makes so much sense then! The line is hooked up on
> the board indeed and I remember being confused why trogdor boards
> don't use it.
>
> I will try to add the suggestions (annotating the reason)
> and verify that it works, would prefer the panel power to be
> gated when possible. I hope this would also fix the initial
> EDID reading issues I occasionally have and carry a hack for
> as of now...
>
> Thank you a lot for this insight!
>
> Nikita
>
> > I guess your other option would be to implement HPD support in
> > ti-sn65dsi86. That would probably be an overall slower boot for you,
> > but is technically more correct. In the past people have posted up
> > patches to get ti-sn65dsi86 working as a full DP port and they added
> > HPD support for that, but none of those patch series ever go to the
> > point of landing...

Yeah, see the big comment in ti_sn65dsi86_enable_comms().

Actually, looking at how the code has evolved in the meantime, you
could probably get away with:

1. Making sure you have an "hpd-absent-delay-ms" in the device tree
for the panel.

2. Implement "wait_hpd_asserted" in ti-sn65dsi86 to simply be a msleep
with the passed in delay.

Then I think you don't need "no-hpd" anywhere which keeps the device
tree pretty.


-Doug