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SubjectRe: [PATCH v2 0/4] drm/bridge: ti-sn65dsi86: Support EDID reading
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Quoting Laurent Pinchart (2021-03-22 17:00:23)
> Hi Stephen,
>
> On Mon, Nov 02, 2020 at 05:15:24PM -0800, Stephen Boyd wrote:
> > Quoting Sam Ravnborg (2020-11-01 09:37:41)
> > > Hi Stephen.
> > >
> > > On Thu, Oct 29, 2020 at 06:17:34PM -0700, Stephen Boyd wrote:
> > > > This patch series cleans up the DDC code a little bit so that
> > > > it is more efficient time wise and supports grabbing the EDID
> > > > of the eDP panel over the aux channel. I timed this on a board
> > > > I have on my desk and it takes about 20ms to grab the EDID out
> > > > of the panel and make sure it is valid.
> > > >
> > > > The first two patches seem less controversial so I stuck them at
> > > > the beginning. The third patch does the EDID reading and caches
> > > > it so we don't have to keep grabbing it over and over again. And
> > > > finally the last patch updates the reply field so that short
> > > > reads and nacks over the channel are reflected properly instead of
> > > > treating them as some sort of error that can't be discerned.
> > > >
> > > > Stephen Boyd (4):
> > > > drm/bridge: ti-sn65dsi86: Combine register accesses in
> > > > ti_sn_aux_transfer()
> > > > drm/bridge: ti-sn65dsi86: Make polling a busy loop
> > > > drm/bridge: ti-sn65dsi86: Read EDID blob over DDC
> > > > drm/bridge: ti-sn65dsi86: Update reply on aux failures
> > >
> > > Series looks good. You can add my a-b on the full series.
> > > Acked-by: Sam Ravnborg <sam@ravnborg.org>
> > >
> > > I can apply after Douglas have had a look at the patches he did not r-b
> > > yet.
> > >
> > > Any chance we can convince you to prepare this bridge driver for use in
> > > a chained bridge setup where the connector is created by the display
> > > driver and uses drm_bridge_funcs?
> > >
> > > First step wuld be to introduce the use of a panel_bridge.
> > > Then add get_edid to drm_bridge_funcs and maybe more helpers.
> > >
> > > Then natural final step would be to move connector creation to the
> > > display driver - see how other uses drm_bridge_connector_init() to do so
> > > - it is relatively simple.
> > >
> > > Should be doable - and reach out if you need some help.
> >
> > I started to look at this and got stuck at ti_sn_bridge_get_bpp(). Where
> > can I get the details of the bpc for the downstream bridge or panel? Is
> > there some function that can tell this bridge what the bpc is for the
> > attached connector?
>
> I've posted a patch series to convert to DRM_BRIDGE_ATTACH_NO_CONNECTOR
> yesterday (and have CC'ed you), but I've overlooked this particular
> problem :-S

!

>
> You can't get the connector in the .enable() operation, but you can get
> it in .atomic_enable(), with
> drm_atomic_get_new_connector_for_encoder(). This being said, it's
> probably not the right option.
>
> What matters here isn't the bpc for the connector, but the format
> expected by the next bridge in the chain. drm_bridge_funcs has two
> operations, .atomic_get_output_bus_fmts() and
> .atomic_get_input_bus_fmts(), to negotiate that format along a chain of
> bridges. The panel bridge driver (drivers/gpu/drm/bridge/panel.c)
> doesn't implement those operations, and neither does
> display-connector.c, so that may be what we should start with.

Ok, makes sense. I'd gladly test things out if you come up with some
solution here.

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