[PATCH v3 02/10] drm/panel: Check for already prepared/enabled in drm_panel

[Maxime Ripard]

Hi,

On Mon, Jul 31, 2023 at 11:33:22AM -0500, Chris Morgan wrote:
> In my case a few different panel drivers disable the regulators in the
> unprepare/disable routines.

And that's totally fine.

> For at least the Rockchip DSI implementations for some reason the
> panel gets unprepared more than once, which triggers an unbalanced
> regulator disable.

"For some reason" being that DW-DSI apparently finds it ok to bypass any
kind of abstraction and randomly calling panel functions by itself:

https://elixir.bootlin.com/linux/v6.4.7/source/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c#L868

It looks like it's fixed it current drm-misc-next though.

> Obviously though the correct course of action is to fix the reason why
> the panel is disabled more than once, but that's at least the root
> cause of this behavior on the few panels I've worked with.

Like I said we already have a commit on the way to fix that, so it
shouldn't be an issue anymore.

I stand by what I was saying earlier though, I think it's mostly
cargo-cult or drivers being very wrong. If anything, the DW-DSI stuff
made me even more convinced that we shouldn't even entertain that idea
:)

Maxime
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