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

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Message-ID: <CAF6AEGvxAVWDC45P3fbmVRO-yq5oV8wgPj0nqC7U0n6c9YuhbQ@mail.gmail.com>
Date: Thu, 18 Jul 2024 09:45:01 -0700
From: Rob Clark <robdclark@...il.com>
To: Doug Anderson <dianders@...omium.org>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org, 
	Rob Clark <robdclark@...omium.org>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] drm/panel/simple-edp: Add Samsung ATNA45DC02

On Thu, Jul 18, 2024 at 9:31 AM Doug Anderson <dianders@...omium.org> wrote:
>
> Hi,
>
> On Thu, Jul 18, 2024 at 9:25 AM Rob Clark <robdclark@...il.com> wrote:
> >
> > On Thu, Jul 18, 2024 at 9:00 AM Doug Anderson <dianders@...omium.org> wrote:
> > >
> > > Hi,
> > >
> > > On Wed, Jul 17, 2024 at 6:09 PM Rob Clark <robdclark@...il.com> wrote:
> > > >
> > > > On Wed, Jul 17, 2024 at 5:19 PM Doug Anderson <dianders@...omium.org> wrote:
> > > > >
> > > > > Hi,
> > > > >
> > > > > On Wed, Jul 17, 2024 at 2:58 PM Rob Clark <robdclark@...il.com> wrote:
> > > > > >
> > > > > > From: Rob Clark <robdclark@...omium.org>
> > > > > >
> > > > > > Just a guess on the panel timings, but they appear to work.
> > > > > >
> > > > > > Signed-off-by: Rob Clark <robdclark@...omium.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.
>
> That would be my best guess. Is there any way for you to find out if
> there's an enable GPIO?

presumably it would be in the ACPI dump (which I've not much of a clue
what I'm looking for there)

BR,
-R

>
> > > 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)
>
> For panels that aren't OLED it's all very standard and we're kinda
> forced to use something generic since manufacturers want lots of 2nd
> (and 3rd and 4th and ...) sourcing. As far as I've been able to tell
> you can't do 2nd sourcing between OLED panels and other panels since
> the wires hooked up to the panels are a little different for the OLED
> panels and the power sequencing is a bit different. It would also be
> pretty obvious to an end user if some of their devices had an OLED
> panel and some didn't. I'm not aware of OLED panels other than the
> Samsung ones, but I haven't done any real research here...
>
> -Doug
>