Re: [PATCH] drm: bridge: fsl-ldb: fixup mode on freq mismatch

[Nikolaus Voss]

Hi Marek,

On 09.12.2024 22:46, Marek Vasut wrote:
> On 12/9/24 9:46 AM, Nikolaus Voss wrote:
> > > > > > and store the panel's timing in EDID EEPROM.
> > > > > Oh, that is a new one. Does the EDID EEPROM store the entirety of
> > > > > 'struct display_timing {}' somehow , or is that a custom format ?
> > > >
> > > > Well, sort of ;-). VESA has taken care of this 30 years ago
> > > > (https://en.wikipedia.org/wiki/Extended_Display_Identification_Data).
> > > >
> > > > DRM handles this with drm_get_edid() and siblings, e.g. :
> > >
> > > EDID can not encode all the information in struct display_timing {} ,
> > > or can it ?
> > >
> > > I think what you would be missing are bus_flags , bus_format and
> > > possibly the single/dual link and channel (odd/even) mapping, won't
> > > you ?
> >
> > Yes, that's right. I use the vendor block for bus_flags and bus_format
> > now, but that's not standard and not portable of course.
> >
> > My first idea was to store the DT overlay in the display EEPROM but
> > a standard 1k EEPROM is too small for that.
> Understood. I had the same problem, in the end I went for custom
> encoding in the EEPROM but the amount of panels was limited in my
> case.
>
> Indeed, DTO does not fit the EEPROM and EDID is not really fitting too
> well to DPI/LVDS panels, it has too many fields that are specific to
> regular pluggable panels and not useful on DPI/LVDS ones.

The curse of backward-compatibility ;-). Nevertheless, we are doing well
with EDID for years now. 95% is implemented in standard kernel, you just
need a few quirks.

--
Nikolaus Voss