linux-kernel - Re: [PATCH 01/20] drm/atomic: Fix remaining places where !funcs->best

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Message-ID: <20160603190151.GD7231@phenom.ffwll.local>
Date:	Fri, 3 Jun 2016 21:01:51 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:	Daniel Vetter <daniel@...ll.ch>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
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	"open list:DRM DRIVERS FOR RENESAS" 
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Subject: Re: [PATCH 01/20] drm/atomic: Fix remaining places where
 !funcs->best_encoder is valid

On Fri, Jun 03, 2016 at 09:37:43AM +0200, Boris Brezillon wrote:
> On Thu, 2 Jun 2016 23:57:02 +0200
> Daniel Vetter <daniel@...ll.ch> wrote:
> 
> > On Thu, Jun 2, 2016 at 11:05 PM, Laurent Pinchart
> > <laurent.pinchart@...asonboard.com> wrote:
> > > Hi Boris,
> > >
> > > Thank you for the patch.
> > >
> > > On Thursday 02 Jun 2016 16:31:28 Boris Brezillon wrote:  
> > >> Adapt drm_pick_crtcs() and update_connector_routing() to fallback to
> > >> drm_atomic_helper_best_encoder() if funcs->best_encoder() is NULL so
> > >> that DRM drivers can leave this hook unassigned if they know they want
> > >> to use drm_atomic_helper_best_encoder().  
> > >
> > > Could you please update include/drm/drm_modeset_helper_vtables.h to document
> > > this new behaviour ?  
> > 
> > Thanks for reminding me. Please update hooks for both
> > atomic_best_encoder and best_encoder. Also mention that it's only
> > optional for atomic drivers. There's lots of examples in that file for
> > the wording usually used.
> 
> Hm, I haven't changed anything for the ->atomic_best_encoder() hook, or
> am I missing something?

Before you needed atomic_best_encoder or best_encoder (well that's the
idea at least), now both are optional. Kerneldoc needs to be adjusted in
both places to match new reality after your patch.
-Daniel

> 
> > 
> > > The only drawback I see in this patch is the additional object lookup
> > > performed by drm_atomic_helper_best_encoder() at runtime. I wonder if we could
> > > somehow cache the information, as the assignment can't change when there's a
> > > 1:1 correspondence between encoders and connectors.  
> > 
> > drm_encoder_find is an idr lookup. That should be plenty fast,
> > especially for modeset code. Usually what's too expensive even for
> > modeset code is linear list walks. But Chris just submitted patches to
> > convert most of them into simple lookups.
> > -Daniel
> > 
> > >>> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>  
> > >> ---
> > >>  drivers/gpu/drm/drm_atomic_helper.c |  4 +++-
> > >>  drivers/gpu/drm/drm_fb_helper.c     | 13 ++++++++++++-
> > >>  2 files changed, 15 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/drivers/gpu/drm/drm_atomic_helper.c
> > >> b/drivers/gpu/drm/drm_atomic_helper.c index f6a3350..849d029 100644
> > >> --- a/drivers/gpu/drm/drm_atomic_helper.c
> > >> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > >> @@ -300,8 +300,10 @@ update_connector_routing(struct drm_atomic_state
> > >> *state, if (funcs->atomic_best_encoder)
> > >>               new_encoder = funcs->atomic_best_encoder(connector,
> > >>                                                        connector_state);
> > >> -     else
> > >> +     else if (funcs->best_encoder)
> > >>               new_encoder = funcs->best_encoder(connector);
> > >> +     else
> > >> +             new_encoder = drm_atomic_helper_best_encoder(connector);
> > >>
> > >>       if (!new_encoder) {
> > >>               DRM_DEBUG_ATOMIC("No suitable encoder found for [CONNECTOR:%d:%s]\n",
> > >> diff --git a/drivers/gpu/drm/drm_fb_helper.c
> > >> b/drivers/gpu/drm/drm_fb_helper.c index 7c2eb75..d44389a 100644
> > >> --- a/drivers/gpu/drm/drm_fb_helper.c
> > >> +++ b/drivers/gpu/drm/drm_fb_helper.c
> > >> @@ -2000,7 +2000,18 @@ static int drm_pick_crtcs(struct drm_fb_helper
> > >> *fb_helper, my_score++;
> > >>
> > >>       connector_funcs = connector->helper_private;
> > >> -     encoder = connector_funcs->best_encoder(connector);
> > >> +
> > >> +     /*
> > >> +      * If the DRM device implements atomic hooks and ->best_encoder() is
> > >> +      * NULL we fallback to the default drm_atomic_helper_best_encoder()
> > >> +      * helper.
> > >> +      */
> > >> +     if (fb_helper->dev->mode_config.funcs->atomic_commit &&
> > >> +         !connector_funcs->best_encoder)
> > >> +             encoder = drm_atomic_helper_best_encoder(connector);
> > >> +     else
> > >> +             encoder = connector_funcs->best_encoder(connector);
> > >> +
> > >>       if (!encoder)
> > >>               goto out;  
> > >
> > > --
> > > Regards,
> > >
> > > Laurent Pinchart
> > >  
> > 
> > 
> > 
> 
> 
> 
> -- 
> Boris Brezillon, Free Electrons
> Embedded Linux and Kernel engineering
> http://free-electrons.com

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch