linux-kernel - Re: [v7 5/5] drm/panel-simple: Add Samsung ATNA33XC20

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Date:   Mon, 21 Jun 2021 08:34:51 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Rajeev Nandan <rajeevny@...eaurora.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Clark <robdclark@...il.com>, Lyude Paul <lyude@...hat.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Rob Herring <robh@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        "Kristian H. Kristensen" <hoegsberg@...omium.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Sean Paul <seanpaul@...omium.org>,
        Kalyan Thota <kalyan_t@...eaurora.org>,
        Krishna Manikandan <mkrishn@...eaurora.org>
Subject: Re: [v7 5/5] drm/panel-simple: Add Samsung ATNA33XC20

Hi,

On Sun, Jun 20, 2021 at 3:01 AM Sam Ravnborg <sam@...nborg.org> wrote:
>
> Hi Rajeev
> On Sat, Jun 19, 2021 at 04:10:30PM +0530, Rajeev Nandan wrote:
> > Add Samsung 13.3" FHD eDP AMOLED panel.
> >
> > Signed-off-by: Rajeev Nandan <rajeevny@...eaurora.org>
> > Reviewed-by: Douglas Anderson <dianders@...omium.org>
> > ---
> >
> > Changes in v4:
> > - New
> >
> > Changes in v5:
> > - Remove "uses_dpcd_backlight" property, not required now. (Douglas)
> >
> > Changes in v7:
> > - Update disable_to_power_off and power_to_enable delays. (Douglas)
> >
> >  drivers/gpu/drm/panel/panel-simple.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> > index 86e5a45..4adc44a 100644
> > --- a/drivers/gpu/drm/panel/panel-simple.c
> > +++ b/drivers/gpu/drm/panel/panel-simple.c
> > @@ -3562,6 +3562,36 @@ static const struct panel_desc rocktech_rk101ii01d_ct = {
> >       .connector_type = DRM_MODE_CONNECTOR_LVDS,
> >  };
> >
> > +static const struct drm_display_mode samsung_atna33xc20_mode = {
> > +     .clock = 138770,
> > +     .hdisplay = 1920,
> > +     .hsync_start = 1920 + 48,
> > +     .hsync_end = 1920 + 48 + 32,
> > +     .htotal = 1920 + 48 + 32 + 80,
> > +     .vdisplay = 1080,
> > +     .vsync_start = 1080 + 8,
> > +     .vsync_end = 1080 + 8 + 8,
> > +     .vtotal = 1080 + 8 + 8 + 16,
> > +     .flags = DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_NVSYNC,
> > +};
> > +
> > +static const struct panel_desc samsung_atna33xc20 = {
> > +     .modes = &samsung_atna33xc20_mode,
> > +     .num_modes = 1,
> > +     .bpc = 10,
> > +     .size = {
> > +             .width = 294,
> > +             .height = 165,
> > +     },
> > +     .delay = {
> > +             .disable_to_power_off = 200,
> > +             .power_to_enable = 400,
> > +             .hpd_absent_delay = 200,
> > +             .unprepare = 500,
> > +     },
> > +     .connector_type = DRM_MODE_CONNECTOR_eDP,
> > +};
>
> bus_format is missing. There should be a warning about this when you
> probe the display.

Sam: I'm curious about the requirement of hardcoding bus_format like
this for eDP panels. Most eDP panels support a variety of bits per
pixel and do so dynamically. Ones I've poked at freely support 6bpp
and 8bpp. Presumably this one supports both of those modes and also
10bpp. I haven't done detailed research on it, but it would also
surprise me if the "bus format" for a given bpp needed to be specified
for eDP. Presumably since eDP has most of the "autodetect" type
features of DP then if the format needed to be accounted for that you
could query the hardware?

Looking at the datasheet for the ti-sn65dsi86 MIPI-to-eDP bridge chip
I see that it explicitly calls out the bus formats that it supports
for the MIPI side but doesn't call out anything for eDP. That would
tend to support my belief that there isn't variance on the eDP side...

Maybe the right fix is to actually change the check not to give a
warning for eDP panels? ...or am I misunderstanding?


> The bpc of 10 in unusual, the current code warns if bpc is neither 6 nor
> 8. If 10 is correct then update the code to accept bpc=10.

I'm pretty sure it's 10 based on this panel's datasheet, though this
panel also accepts 8 bpc. Fixing the warning seems like a good idea to
me--I wasn't aware of it.

-Doug