linux-kernel - Re: [PATCH RFC 03/10] drm/panel: Add LGD panel driver for Sony Xperia XZ3

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Message-ID: <ao2w7eiuc4olqbycmdviqrpqbdpoltusixlllied7jbo5fucap@xv6xvgi43yio>
Date:   Tue, 30 May 2023 10:27:23 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     neil.armstrong@...aro.org, Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Caleb Connolly <caleb@...nolly.tech>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        Jessica Zhang <quic_jesszhan@...cinc.com>
Subject: Re: [PATCH RFC 03/10] drm/panel: Add LGD panel driver for Sony
 Xperia XZ3

On 2023-05-30 01:39:10, Dmitry Baryshkov wrote:
> On 30/05/2023 01:37, Marijn Suijten wrote:
> > On 2023-05-30 01:18:40, Dmitry Baryshkov wrote:
> > <snip>
> >>>>>>> +    ret = mipi_dsi_dcs_set_display_on(dsi);
> >>>>>>> +    if (ret < 0) {
> >>>>>>> +        dev_err(dev, "Failed to turn display on: %d\n", ret);
> >>>>>>> +        return ret;
> >>>>>>> +    }
> >>>>>>
> >>>>>> My usual question: should the mipi_dsi_dcs_exit_sleep_mode() / mipi_dsi_dcs_set_display_on() be moved from prepare() to enable() part?
> >>>>>
> >>>>>
> >>>>> No, prepare is called before the video stream is started and when display is still in LPM mode and the mode hasn't been set.
> >>>>>
> >>>>
> >>>> Yes, that's my point. Shouldn't we enable the panel _after_ starting the stream?
> >>>
> >>> I have never investigated what it takes to split these functions, but
> >>> some of these panels do show some corruption at startup which may be
> >>> circumvented by powering the panel on after starting the video stream?
> >>>
> >>> I'm just not sure where to make the split: downstream does describe a
> >>> qcom,mdss-dsi-on-command and qcom,mdss-dsi-post-panel-on-command, where
> >>> the latter only contains set_display_on() (not exit_sleep_mode()).
> >>> It is documented like:
> >>>
> >>>       same as "qcom,mdss-dsi-on-command" except commands are sent after
> >>>       displaying an image."
> >>>
> >>> So this seems like the right way to split them up, I'll test this out on
> >>> all submitted panel drivers.
> >>
> >> Interesting enough, Neil suggested that sending all the commands during
> >> pre_enable() is the correct sequence (especially for VIDEO mode panels),
> >> since not all DSI hosts can send commands after switching to the VIDEO mode.
> > 
> > Note that all these panels and Driver-ICs are command-mode, and/or
> > programmed to run in command-mode, so there shouldn't be any notion of a
> > VIDEO stream (any command-mode frame is just an "arbitrary command" as
> > far as I understood).
> 
> Yes, from the data stream point of view. I was talking about the DSI 
> host being able to send arbitrary commands or not after enabling the 
> video/cmd stream.

Is this a known limitation of SM8250 then?  Or is the brightness_set
issue more likely a "problem" with the panel that the downstream kernel
is "somehow" working around or aware of, and I just haven't found
how/where it deals with that?
(Alternatively we could be "doing it wrong" for other panels but it
 turns out to be working anyway)

- Marijn