linux-kernel - Re: [RFC PATCH v2 3/9] drm/panel: nv3052c: Sleep for 150ms after reset

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Message-ID: <ZQjD6gCEo62gMBX2@titan>
Date:   Tue, 19 Sep 2023 07:40:58 +1000
From:   John Watts <contact@...kia.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Jessica Zhang <quic_jesszhan@...cinc.com>,
        dri-devel@...ts.freedesktop.org,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Chris Morgan <macromorgan@...mail.com>,
        Jagan Teki <jagan@...eble.ai>,
        Christophe Branchereau <cbranchereau@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 3/9] drm/panel: nv3052c: Sleep for 150ms after
 reset

On Mon, Sep 18, 2023 at 11:34:51PM +0200, Paul Cercueil wrote:
> The driver is guaranteed to always reset the panel in sleep-in mode -
> as long as the panel was off when the driver started.
> 
> What I'd suggest if you really need to support a case where the panel
> was enabled by the bootloader, is to read the 0x0a register after
> enabling the regulator to read the mode, and sleep 120ms if it was in
> sleep-out mode.
> 
> But that's only if it's a case that you can test with. I won't accept a
> patch that makes sense on the surface if it addresses a corner case
> that nobody ever tested for.
> 
> For what I know, this patch just adds a huge delay to panel boot-up for
> all existing users for no valid reason.
>
> 
> Cheers,
> -Paul

Thank you very much for this feedback. I am more than happy to throw these
sleep patches in the trash and come back later with a proper solution when
I have an actual hardware setup and use case to test on.

John.