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From:   cong yang <yangcong5@huaqin.corp-partner.google.com>
Date:   Fri, 7 Jul 2023 09:20:43 +0800
Message-ID: <CAHwB_NJbtvXNCFj5=NMBXWCt1S1_WrgGij2Kqdr1omno66kVUw@mail.gmail.com>
Subject: Re: [PATCH] drm/panel: Add avdd/avee delay for Starry-himax83102-j02
 and Starry-ili9882t panel
To:     Doug Anderson <dianders@google.com>
Cc:     sam@ravnborg.org, neil.armstrong@linaro.org, daniel@ffwll.ch,
        airlied@gmail.com, hsinyi@google.com,
        dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org
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Hi,

On Fri, Jul 7, 2023 at 3:32=E2=80=AFAM Doug Anderson <dianders@google.com> =
wrote:
>
> Hi,
>
> On Mon, Jul 3, 2023 at 10:07=E2=80=AFPM Cong Yang
> <yangcong5@huaqin.corp-partner.google.com> wrote:
> >
> > From power on/off sequence for panel data sheet[1], T2 timing VSP to VS=
N
> > 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 o=
f
> > 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.

The regulator device tree has only the power on attribute
"regulator-enable-ramp-delay",
not has power off attribute. The regulator delay looks more like the
HW voltage requirement
of the power ic itself, and I just want to meet the panel spec
requirement. I add regulator-enable-ramp-delay
in dts he can also meet my requirement, but I have no way to control
the power off delays.

Thanks Doug.

>
> -Doug