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

[Daniel Vetter]

On Fri, May 12, 2017 at 02:01:49PM +0300, Laurent Pinchart wrote:
> Hi Archit,
> 
> On Friday 12 May 2017 16:20:07 Archit Taneja wrote:
> > On 05/12/2017 03:08 PM, Laurent Pinchart wrote:
> > > On Wednesday 10 May 2017 17:14:33 Daniel Vetter wrote:
> > >> 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@xxxxxxxxxxxx>
> > >>>> Cc: Carlos Palminha <palminha@xxxxxxxxxxxx>
> > >>>> Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
> > >>>> Cc: Ville Syrjälä <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.
> 
> And now that I think about it, for some of the operations (especially 
> enable/disable) I believe that the bridge should be able to decide whether to 
> call the next/previous bridge first or to configure its hardware first. I can 
> image bridges that need the previous bridge in the chain to provide a valid 
> clock before they get started, as well as bridges that need to be started with 
> the incoming video signal stopped.

That's why we have pre_/post_ hooks ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch