[RFC] drm/panel/simple-edp: Add Samsung ATNA45DC02

[Rob Clark]

On Thu, Jul 18, 2024 at 9:00 AM Doug Anderson <dianders at chromium.org> wrote:
>
> Hi,
>
> On Wed, Jul 17, 2024 at 6:09 PM Rob Clark <robdclark at gmail.com> wrote:
> >
> > On Wed, Jul 17, 2024 at 5:19 PM Doug Anderson <dianders at chromium.org> wrote:
> > >
> > > Hi,
> > >
> > > On Wed, Jul 17, 2024 at 2:58 PM Rob Clark <robdclark at gmail.com> wrote:
> > > >
> > > > From: Rob Clark <robdclark at chromium.org>
> > > >
> > > > Just a guess on the panel timings, but they appear to work.
> > > >
> > > > Signed-off-by: Rob Clark <robdclark at chromium.org>
> > > > ---
> > > > This adds the panel I have on my lenovo yoga slim 7x laptop.  I couldn't
> > > > find any datasheet so timings is just a guess.  But AFAICT everything
> > > > works fine.
> > > >
> > > >  drivers/gpu/drm/panel/panel-edp.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > >
> > > Given that this is a Samsung ATNA<mumble>, is there any chance it's an
> > > OLED panel? Should it be supported with the Samsung OLED panel driver
> > > like this:
> > >
> > > https://lore.kernel.org/r/20240715-x1e80100-crd-backlight-v2-0-31b7f2f658a3@linaro.org
> >
> > it is an OLED panel, and I did see that patchset and thought that
> > samsung panel driver would work.  But changing the compat string on
> > the yoga dts only gave me a black screen (and I didn't see any of the
> > other mentioned problems with bl control or dpms with panel-edp).  So
> > :shrug:?  It could be I overlooked something else, but it _seems_ like
> > panel-edp is fine for this panel. Plus, it would avoid awkwardness if
> > it turned out there were other non-samsung 2nd sources, but so far
> > with a sample size of two 100% of these laptops have the same panel
>
> Hmm, OK. One question for you: are you using the "enable" GPIO in
> panel-edp? IMO the code handling that GPIO in panel-edp is somewhat
> dodgy, but it predates my deeper involvement with panels. I've never
> seen an eDP panel that could use panel-edp where it was actually
> required--every instance where someone thought it was required was
> better modeled by using that GPIO as the backlight enable. On the
> other hand, the "enable" GPIO in the Samsung OLED panel driver came
> straight from the panel datasheet and it makes sense for it to be in
> the panel driver since the backlight is handled straight by the
> panel...

hmm, at least current dts doesn't have an enable gpio.  Which could be
why panel-samsung-atna33xc20 wasn't working.

It is entirely possible we are relying on something left on by the bootloader.

> In any case, I guess if things are working it doesn't really hurt to
> take it in panel-edp for now...
>

I wonder if using compatible="edp-panel" everywhere isn't a great idea
if we want to switch drivers later.  But I guess that is already water
under the bridge (so to speak)

BR,
-R

> > But that was the reason for posting this as an RFC.  I was hoping
> > someone had some hint about where to find datasheets (my google'ing
> > was not successful), etc.
>
> I don't personally have any hints.
>
> -Doug
>