[RFC PATCH] drm/panel: synaptics-r63353: Fix regulator unbalance

[Doug Anderson]

Hi,

On Wed, Aug 7, 2024 at 5:39 AM Michael Nazzareno Trimarchi
<michael at amarulasolutions.com> wrote:
>
> Hi Doug
>
> +cc Doug
>
> I have seen that you have done some re-working and investigation on
> drm stack, do you have some
> suggestion on this case?
>
> On Mon, Jun 24, 2024 at 8:53 PM Michael Trimarchi
> <michael at amarulasolutions.com> wrote:
> >
> > The shutdown function can be called when the display is already
> > unprepared. For example during reboot this trigger a kernel
> > backlog. Calling the drm_panel_unprepare, allow us to avoid
> > to trigger the kernel warning
> >
> > Signed-off-by: Michael Trimarchi <michael at amarulasolutions.com>
> > ---
> >
> > It's not obviovus if shutdown can be dropped or this problem depends
> > on the display stack as it is implmented. More feedback is required
> > here

In general the shutdown should be dropped and it should be up to the
display driver to do the shutdown. If your panel needs to be used with
a DRM Modeset driver that doesn't properly call shutdown then the
ideal solution would be to fix the DRM Modeset driver. If this is
somehow impossible, I suspect folks would (begrudgingly) accept some
other solution.

>From a super quick look, I see:

* This panel seems to be used upstream by "imx8mn-bsh-smm-s2-display.dtsi"

* In "imx8mn.dtsi" I see "lcdif" is "fsl,imx6sx-lcdif".

* "fsl,imx6sx-lcdif" seems to be handled by "drivers/gpu/drm/mxsfb/mxsfb_drv.c"

* Previously I determined that "mxsfb-drm" was indeed calling
drm_atomic_helper_shutdown() properly [1]

...so it seems like just dropping the shutdown handler in this panel is correct.


[1] https://lore.kernel.org/r/20240611074846.1.Ieb287c2c3ee3f6d3b0d5f49b29f746b93621749c@changeid

-Doug