linux-kernel - Re: [PATCH] drm/panel: Add avdd/avee delay for Starry-himax83102-j02 and Starry-ili9882t panel

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Date:   Thu, 6 Jul 2023 12:32:26 -0700
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,
        airlied@...il.com, hsinyi@...gle.com,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: Add avdd/avee delay for Starry-himax83102-j02
 and Starry-ili9882t panel

Hi,

On Mon, Jul 3, 2023 at 10:07 PM Cong Yang
<yangcong5@...qin.corp-partner.google.com> wrote:
>
> From power on/off sequence for panel data sheet[1], T2 timing VSP to VSN
> needs 1ms delay when power on, and VSN to VSP also needs 1ms delay when
> power off. Some pmic may not be able to adjust the delay internally, so
> let's add a delay between avdd/avee regulator gpio to meet the timing of
> panel.

Unless I'm mistaken, all of this is best handled via regulator
constraints in the device tree. See the file:

Documentation/devicetree/bindings/regulator/regulator.yaml

Specifically, any delays related to actually ramping up / down the
regulator can be specified in the device tree. Nominally, you could
argue that the 1 ms delay actually _does_ belong in the driver, but
IMO the 1 ms number there is really just there because someone thought
it was weird to specify a delay of 0 ms. Given that you already need
remp delays in the device tree, it feels OK to me to just include the
1 ms there.

-Doug