linux-kernel - Re: [Patch 1/1] drm/atomic: integrate private objects with suspend/resume helpers

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Message-ID: <20190325090641.GF2665@phenom.ffwll.local>
Date:   Mon, 25 Mar 2019 10:06:41 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Benoit Parrot <bparrot@...com>
Cc:     Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Jyri Sarha <jsarha@...com>
Subject: Re: [Patch 1/1] drm/atomic: integrate private objects with
 suspend/resume helpers

On Fri, Mar 15, 2019 at 06:56:07AM -0500, Benoit Parrot wrote:
> Daniel Vetter <daniel@...ll.ch> wrote on Fri [2019-Mar-15 11:50:57 +0100]:
> > On Thu, Mar 14, 2019 at 08:44:45AM -0500, Benoit Parrot wrote:
> > > During a suspend cycle the atomic state is saved to be used during the
> > > restore cycle.
> > > 
> > > However the current state duplication logic does not duplicate private
> > > objects. This leads to state inconsistencies at resume time.
> > > 
> > > With private objects modeset lock now integrated, we can make sure that
> > > private object state are properly saved and restored.
> > > 
> > > Signed-off-by: Benoit Parrot <bparrot@...com>
> > 
> > Why do you need this? We're doing a full atomic_check, and your
> > atomic_check should be pulling in any private state objects and
> > recomputing their states. This smells like papering over a driver bug.
> 
> I have not seen any atomic_check called during the suspend duplicate
> helper. And you are correct normally the private_object state in my case
> would get pulled in during a plane atomic_check but that does not happen
> here in this step.

Yeah duplicating in suspend won't call atomic_check. Restoring the
duplicated state on resume will (or there's going to be lots of broken
drivers).

> Why wouldn't we save all the "state" artifacts so that the whole atomic
> state is consistent?

It's not needed, and might possible paper over driver bugs ...

> > The duplicate helpers should only need to duplicate the uapi-relevant
> > states, i.e. connector/crtc/planes.

... because of this reason. If your driver can't recompute the private
state from just the duplicated uapi-relevant states it's broken. Because
essentially the exact same thing might happen through the atomic ioctl
from userspace.

Hence my question: Why do you need this?
-Daniel

> > -Daniel
> > 
> > > ---
> > >  drivers/gpu/drm/drm_atomic_helper.c | 16 ++++++++++++++++
> > >  1 file changed, 16 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > > index 540a77a2ade9..b108021cc092 100644
> > > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > > @@ -3189,6 +3189,7 @@ drm_atomic_helper_duplicate_state(struct drm_device *dev,
> > >  	struct drm_connector_list_iter conn_iter;
> > >  	struct drm_plane *plane;
> > >  	struct drm_crtc *crtc;
> > > +	struct drm_private_obj *privobj;
> > >  	int err = 0;
> > >  
> > >  	state = drm_atomic_state_alloc(dev);
> > > @@ -3218,6 +3219,16 @@ drm_atomic_helper_duplicate_state(struct drm_device *dev,
> > >  		}
> > >  	}
> > >  
> > > +	drm_for_each_privobj(privobj, dev) {
> > > +		struct drm_private_state *priv_state;
> > > +
> > > +		priv_state = drm_atomic_get_private_obj_state(state, privobj);
> > > +		if (IS_ERR(priv_state)) {
> > > +			err = PTR_ERR(priv_state);
> > > +			goto free;
> > > +		}
> > > +	}
> > > +
> > >  	drm_connector_list_iter_begin(dev, &conn_iter);
> > >  	drm_for_each_connector_iter(conn, &conn_iter) {
> > >  		struct drm_connector_state *conn_state;
> > > @@ -3325,12 +3336,17 @@ int drm_atomic_helper_commit_duplicated_state(struct drm_atomic_state *state,
> > >  	struct drm_connector_state *new_conn_state;
> > >  	struct drm_crtc *crtc;
> > >  	struct drm_crtc_state *new_crtc_state;
> > > +	struct drm_private_obj *privobj;
> > > +	struct drm_private_state *new_priv_state;
> > >  
> > >  	state->acquire_ctx = ctx;
> > >  
> > >  	for_each_new_plane_in_state(state, plane, new_plane_state, i)
> > >  		state->planes[i].old_state = plane->state;
> > >  
> > > +	for_each_new_private_obj_in_state(state, privobj, new_priv_state, i)
> > > +		state->private_objs[i].old_state = privobj->state;
> > > +
> > >  	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i)
> > >  		state->crtcs[i].old_state = crtc->state;
> > >  
> > > -- 
> > > 2.17.1
> > > 
> > 
> > -- 
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > http://blog.ffwll.ch
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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

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