linux-kernel - Re: [PATCH v2 6/8] drm: Introduce drm_bridge_mode

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Date:   Wed, 10 May 2017 17:14:33 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
Cc:     Jose Abreu <Jose.Abreu@...opsys.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Carlos Palminha <CARLOS.PALMINHA@...opsys.com>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Dave Airlie <airlied@...ux.ie>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Archit Taneja <architt@...eaurora.org>
Subject: Re: [PATCH v2 6/8] drm: Introduce drm_bridge_mode_valid()

On Wed, May 10, 2017 at 04:41:09PM +0300, Ville Syrjälä 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@...opsys.com>
> > Cc: Carlos Palminha <palminha@...opsys.com>
> > Cc: Alexey Brodkin <abrodkin@...opsys.com>
> > Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
> > Cc: Daniel Vetter <daniel.vetter@...ll.ch>
> > Cc: Dave Airlie <airlied@...ux.ie>
> > Cc: Andrzej Hajda <a.hajda@...sung.com>
> > Cc: Archit Taneja <architt@...eaurora.org>
> > ---
> >  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).
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch