[PATCH v3 4/6] drm/tidss: Set bus_format correctly from bridge/connector

[Laurent Pinchart]

Hi Nikhil,

On Mon, Nov 30, 2020 at 12:05:03PM +0530, Nikhil Devshatwar wrote:
> On 14:51-20201125, Tomi Valkeinen wrote:
> > On 19/11/2020 18:01, Nikhil Devshatwar wrote:
> > > Remove the old code to iterate over the bridge chain, as this is
> > > already done by the framework.
> > > The bridge state should have the negotiated bus format and flags.
> > > Use these from the bridge's state.
> > > If the bridge does not support format negotiation, error out
> > > and fail.
> > > 
> > > Signed-off-by: Nikhil Devshatwar <nikhil.nd at ti.com>
> > > Reviewed-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
> > > ---
> > > 
> > > Notes:
> > >     changes from v2:
> > >     * Remove the old code and use the flags from the bridge state
> > > 
> > >  drivers/gpu/drm/tidss/tidss_encoder.c | 36 +++++++++++----------------
> > >  1 file changed, 14 insertions(+), 22 deletions(-)
> > 
> > If a first bridge (after the crtc) supports two bus formats as input, how does tidss choose between
> > those? This patch just picks bstate->input_bus_cfg.format, and it's not clear to me which one that
> > is (the first one?). Also, we don't check if tidss actually supports the bus format.
> 
> The selection is done by the framework in
> select_bus_fmt_recursive at drivers/gpu/drm/drm_bridge.c:810
> 
> My understanding is that currently, the format negotiation logic does
> not negotiate all the way till encoder, it stops only at the
> first_bridge.

Should we then implement a bridge in the tidss driver to model the
internal encoder, in order to support format negotiation all the way to
the tidss ?

-- 
Regards,

Laurent Pinchart