Re: [PATCH v6 4/6] drm/fence: add in-fences support

[Gustavo Padovan <gustavo@padovan.org>]

2016-10-28 Daniel Vetter <daniel@ffwll.ch>:

> On Thu, Oct 27, 2016 at 05:37:09PM -0200, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> > 
> > There is now a new property called FENCE_FD attached to every plane
> > state that receives the sync_file fd from userspace via the atomic commit
> > IOCTL.
> > 
> > The fd is then translated to a fence (that may be a fence_collection
> > subclass or just a normal fence) and then used by DRM to fence_wait() for
> > all fences in the sync_file to signal. So it only commits when all
> > framebuffers are ready to scanout.
> > 
> > v2: Comments by Daniel Vetter:
> > 	- remove set state->fence = NULL in destroy phase
> > 	- accept fence -1 as valid and just return 0
> > 	- do not call fence_get() - sync_file_fences_get() already calls it
> > 	- fence_put() if state->fence is already set, in case userspace
> > 	set the property more than once.
> > 
> > v3: WARN_ON if fence is set but state has no FB
> > 
> > v4: Comment from Maarten Lankhorst
> > 	- allow set fence with no related fb
> > 
> > v5: rename FENCE_FD to IN_FENCE_FD
> > 
> > v6: Comments by Daniel Vetter:
> > 	- rename plane_state->in_fence back to "fence"
> > 
> >      - rebase after fence -> dma_fence rename
> > 
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
> 
> Looks good, but I'll wait with full review with all the fence patches
> until the igts show up. It's much easier to check for gabs in input
> validation code if you also have the testcases at hand. A few comments
> below.
> -Daniel
> 
> > ---
> >  drivers/gpu/drm/Kconfig             |  1 +
> >  drivers/gpu/drm/drm_atomic.c        | 15 +++++++++++++++
> >  drivers/gpu/drm/drm_atomic_helper.c |  5 +++--
> >  drivers/gpu/drm/drm_crtc.c          |  6 ++++++
> >  drivers/gpu/drm/drm_plane.c         |  1 +
> >  include/drm/drm_crtc.h              |  5 +++++
> >  6 files changed, 31 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index 483059a..43cb33d 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -12,6 +12,7 @@ menuconfig DRM
> >  	select I2C
> >  	select I2C_ALGOBIT
> >  	select DMA_SHARED_BUFFER
> > +	select SYNC_FILE
> >  	help
> >  	  Kernel-level support for the Direct Rendering Infrastructure (DRI)
> >  	  introduced in XFree86 4.0. If you say Y here, you need to select
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 5e73954..28d9366 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -30,6 +30,7 @@
> >  #include <drm/drm_atomic.h>
> >  #include <drm/drm_mode.h>
> >  #include <drm/drm_plane_helper.h>
> > +#include <linux/sync_file.h>
> >  
> >  #include "drm_crtc_internal.h"
> >  
> > @@ -686,6 +687,17 @@ int drm_atomic_plane_set_property(struct drm_plane *plane,
> >  		drm_atomic_set_fb_for_plane(state, fb);
> >  		if (fb)
> >  			drm_framebuffer_unreference(fb);
> > +	} else if (property == config->prop_in_fence_fd) {
> > +		if (U642I64(val) == -1)
> > +			return 0;
> > +
> > +		if (state->fence)
> > +			dma_fence_put(state->fence);
> > +
> > +		state->fence = sync_file_get_fence(val);
> > +		if (!state->fence)
> > +			return -EINVAL;
> > +
> >  	} else if (property == config->prop_crtc_id) {
> >  		struct drm_crtc *crtc = drm_crtc_find(dev, val);
> >  		return drm_atomic_set_crtc_for_plane(state, crtc);
> > @@ -747,6 +759,8 @@ drm_atomic_plane_get_property(struct drm_plane *plane,
> >  
> >  	if (property == config->prop_fb_id) {
> >  		*val = (state->fb) ? state->fb->base.id : 0;
> > +	} else if (property == config->prop_in_fence_fd) {
> > +		*val = -1;
> >  	} else if (property == config->prop_crtc_id) {
> >  		*val = (state->crtc) ? state->crtc->base.id : 0;
> >  	} else if (property == config->prop_crtc_x) {
> > @@ -1752,6 +1766,7 @@ int drm_mode_atomic_ioctl(struct drm_device *dev,
> >  		drm_mode_object_unreference(obj);
> >  	}
> >  
> > +
> 
> Spurios whitespace.
> 
> >  	if (arg->flags & DRM_MODE_PAGE_FLIP_EVENT) {
> >  		for_each_crtc_in_state(state, crtc, crtc_state, i) {
> >  			struct drm_pending_vblank_event *e;
> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> > index 75ad01d..c34da9e 100644
> > --- a/drivers/gpu/drm/drm_atomic_helper.c
> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
> > @@ -1034,8 +1034,6 @@ int drm_atomic_helper_wait_for_fences(struct drm_device *dev,
> >  		if (!plane_state->fence)
> >  			continue;
> >  
> > -		WARN_ON(!plane_state->fb);
> > -
> 
> Why this? We don't allow a plane to be enabled without an fb, and adding a
> fence to a plane which is disabled sounds likea  bug. We probably should
> have a bit of code in the core atomic check code to make sure userspace
> never asks for a fence when the plane is off.

This was Maarten's suggestion that we should be able to sent a fence to
determine when then plane should be disabled. Not sure which usecase he
had in mind.

Gustavo