Re: [PATCH v2 6/8] drm: Introduce drm_bridge_mode_valid()

[Archit Taneja]

On 05/12/2017 03:08 PM, Laurent Pinchart wrote:
> Hi Daniel,
>
> On Wednesday 10 May 2017 17:14:33 Daniel Vetter wrote:
> > On Wed, May 10, 2017 at 04:41:09PM +0300, Ville SyrjÃlà wrote:
> > > On Tue, May 09, 2017 at 06:00:13PM +0100, Jose Abreu wrote:
> > > > Introduce a new helper function which calls mode_valid() callback
> > > > for all bridges in an encoder chain.
> > > >
> > > > Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>
> > > > Cc: Carlos Palminha <palminha@xxxxxxxxxxxx>
> > > > Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> > > > Cc: Ville SyrjÃlà <ville.syrjala@xxxxxxxxxxxxxxx>
> > > > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
> > > > Cc: Dave Airlie <airlied@xxxxxxxx>
> > > > Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> > > > Cc: Archit Taneja <architt@xxxxxxxxxxxxxx>
> > > > ---
> > > >
> > > >  drivers/gpu/drm/drm_bridge.c | 33 +++++++++++++++++++++++++++++++++
> > > >  include/drm/drm_bridge.h     |  2 ++
> > > >  2 files changed, 35 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> > > > index 86a7637..dc8cdfe 100644
> > > > --- a/drivers/gpu/drm/drm_bridge.c
> > > > +++ b/drivers/gpu/drm/drm_bridge.c
> > > > @@ -206,6 +206,39 @@ bool drm_bridge_mode_fixup(struct drm_bridge
> > > > *bridge,
> > > >
> > > >  EXPORT_SYMBOL(drm_bridge_mode_fixup);
> > > >
> > > >  /**
> > > >
> > > > + * drm_bridge_mode_valid - validate the mode against all bridges in the
> > > > + * 			   encoder chain.
> > > > + * @bridge: bridge control structure
> > > > + * @mode: desired mode to be validated
> > > > + *
> > > > + * Calls &drm_bridge_funcs.mode_valid for all the bridges in the
> > > > encoder
> > > > + * chain, starting from the first bridge to the last. If at least one
> > > > bridge + * does not accept the mode the function returns the error
> > > > code.
> > > > + *
> > > > + * Note: the bridge passed should be the one closest to the encoder.
> > > > + *
> > > > + * RETURNS:
> > > > + * MODE_OK on success, drm_mode_status Enum error code on failure
> > > > + */
> > > > +enum drm_mode_status drm_bridge_mode_valid(struct drm_bridge *bridge,
> > > > +					   const struct drm_display_mode
> *mode)
> > > > +{
> > > > +	enum drm_mode_status ret = MODE_OK;
> > > > +
> > > > +	if (!bridge)
> > > > +		return ret;
> > > > +
> > > > +	if (bridge->funcs->mode_valid)
> > > > +		ret = bridge->funcs->mode_valid(bridge, mode);
> > > > +
> > > > +	if (ret != MODE_OK)
> > > > +		return ret;
> > > > +
> > > > +	return drm_bridge_mode_valid(bridge->next, mode);
> > >
> > > Looks like it should be pretty trivial to avoid the recursion.
> > >
> > > Am I correct in interpreting this that bridges have some kind of
> > > a hand rolled linked list implementation? Reusing the standard
> > > linked lists would allow you to use list_for_each() etc.
> >
> > Yeah it's a hand-rolled list, but current hw also has a bridge nesting
> > depth of 2, so it really doesn't matter. I guess once we have real long
> > chains of bridges we can fix this (and just using list_head sounds like a
> > great idea).
>
> Even if not really needed right now, it's a pretty easy cleanup, if Jose has
> time to handle it in v3 of this series let's not postpone it ;-)

jfyi, some of the bridge functions call the ops from the last bridge in the
chain to first, so we'd need to use list_for_each_entry_prev() (or something
like that) for them.

Archit

--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project