On Mon, Sep 04, 2023 at 01:04:40PM +0300, Jani Nikula wrote:
> On Sat, 02 Sep 2023, Peter Senna Tschudin wrote:
> > Good morning Jani,
> >
> > It has been a long time since I wrote the driver, and many many years
> > since I sent my last kernel patch, so my memory does not serve me very
> > well, but I will try to shed some light.
> >
> > On Fri, Sep 1, 2023 at 12:24 PM Jani Nikula wrote:
> >>
> >> The driver was originally added in commit fcfa0ddc18ed ("drm/bridge:
> >> Drivers for megachips-stdpxxxx-ge-b850v3-fw (LVDS-DP++)"). I tried to
> >> look up the discussion, but didn't find anyone questioning the EDID
> >> reading part.
> >>
> >> Why does it not use drm_get_edid() or drm_do_get_edid()?
> >>
> >> I don't know where client->addr comes from, so I guess it could be
> >> different from DDC_ADDR, rendering drm_get_edid() unusable.
> >>
> >> There's also the comment:
> >>
> >> /* Yes, read the entire buffer, and do not skip the first
> >> * EDID_LENGTH bytes.
> >> */
> >>
> >> But again, there's not a word on *why*.
> >
> > The video pipeline has two hardware bridges between the LVDS from the
> > SoC and DP+ output. For reasons, we would get hot plug events from one
> > of these bridges, and EDID from the other. If I am not mistaken, I
> > documented this strangeness in the DTS readme file.
This should be supported properly by the drm_bridge_connector helper,
which supports delegating HPD and EDID retrieval to different bridges.
> > Did this shed any light on the *why* or did I tell you something you
> > already knew?
>
> I guess that answers the question why it's necessary to specify the ddc
> to use, but not why drm_do_get_edid() could not be used. Is it really
> necessary to read the EDID in one go?
--
Regards,
Laurent Pinchart
