Re: [PATCH] drm: rcar-du: track dma-buf fences

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Apr 4, 2018 at 12:59 PM, Ucan, Emre (ADITG/ESB)
<eucan@de.adit-jv.com> wrote:
> Hello Laurent
>
> Thank you for your review.
>
>> -----Original Message-----
>> From: Laurent Pinchart [mailto:laurent.pinchart@ideasonboard.com]
>> Sent: Dienstag, 3. April 2018 20:53
>> To: Ucan, Emre (ADITG/ESB)
>> Cc: dri-devel@lists.freedesktop.org
>> Subject: Re: [PATCH] drm: rcar-du: track dma-buf fences
>>
>> Hello Emre,
>>
>> Thank you for the patch.
>>
>> On Tuesday, 3 April 2018 12:14:33 EEST Emre Ucan wrote:
>> > We have to check dma-buf reservation objects
>> > of our framebuffers before we use them.
>> > Otherwise, another driver might be writing
>> > on the same buffer which we are using.
>> > This would cause visible tearing effects
>> > on display.
>> >
>> > We can use existing atomic helper functions
>> > to solve this problem.
>> >
>> > Signed-off-by: Emre Ucan <eucan@de.adit-jv.com>
>> > ---
>> >  drivers/gpu/drm/rcar-du/rcar_du_kms.c |  2 ++
>> >  drivers/gpu/drm/rcar-du/rcar_du_vsp.c | 20 ++++++++++++++++++++
>> >  2 files changed, 22 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_kms.c
>> > b/drivers/gpu/drm/rcar-du/rcar_du_kms.c index 0329b35..f3da3d1 100644
>> > --- a/drivers/gpu/drm/rcar-du/rcar_du_kms.c
>> > +++ b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
>> > @@ -255,6 +255,8 @@ static void rcar_du_atomic_commit_tail(struct
>> > drm_atomic_state *old_state) {
>> >     struct drm_device *dev = old_state->dev;
>> >
>> > +   drm_atomic_helper_wait_for_fences(dev, old_state, false);
>> > +
>>
>> The commit_tail() function in drm_atomic_helper.c, which calls our
>> atomic_commit_tail() implementation, already calls
>> drm_atomic_helper_wait_for_fences(). Why is there a need to duplicate the
>> call
>> here ?
>
> You are right. I will remove it in second version.

You can use it in your own hook. Patch to update the kerneldoc to
clarify that would be great.
-Daniel

>
>>
>> >     /* Apply the atomic update. */
>> >     drm_atomic_helper_commit_modeset_disables(dev, old_state);
>> >     drm_atomic_helper_commit_planes(dev, old_state,
>> > diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
>> > b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c index 2c260c3..482e23c 100644
>> > --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
>> > +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
>> > @@ -18,12 +18,16 @@
>> >  #include <drm/drm_fb_cma_helper.h>
>> >  #include <drm/drm_gem_cma_helper.h>
>> >  #include <drm/drm_plane_helper.h>
>> > +#include <drm/drm_atomic.h>
>> >
>> >  #include <linux/bitops.h>
>> >  #include <linux/dma-mapping.h>
>> > +#include <linux/dma-fence.h>
>> > +#include <linux/dma-buf.h>
>> >  #include <linux/of_platform.h>
>> >  #include <linux/scatterlist.h>
>> >  #include <linux/videodev2.h>
>> > +#include <linux/reservation.h>
>> >
>> >  #include <media/vsp1.h>
>> >
>> > @@ -203,6 +207,20 @@ static void rcar_du_vsp_plane_setup(struct
>> > rcar_du_vsp_plane *plane) plane->index, &cfg);
>> >  }
>> >
>> > +static void rcar_du_vsp_set_fence_for_plane(struct drm_plane_state
>> *state)
>> > +{
>> > +   struct drm_gem_cma_object *gem;
>> > +   struct dma_buf *dma_buf;
>> > +   struct dma_fence *fence;
>> > +
>> > +   gem = drm_fb_cma_get_gem_obj(state->fb, 0);
>> > +   dma_buf = gem->base.dma_buf;
>> > +   if (dma_buf) {
>> > +           fence = reservation_object_get_excl_rcu(dma_buf->resv);
>> > +           drm_atomic_set_fence_for_plane(state, fence);
>>
>> Unless I'm mistaken this is used for implicit fencing only. What is your use
>> case, wouldn't it be better for userspace to use explicit fencing as that is
>> the fence model that has been selected for display ?
>
> We are using Weston on Renesas R-Car H3 SoC. I am using GPU rendered client buffers
> directly as scanout buffer for the display. Weston is not using explicit fencing.
>
>>
>> > +   }
>> > +}
>>
>> This looks very similar to drm_gem_fb_prepare_fb(), couldn't you use that
>> function instead ?
>
> Description of drm_gem_fb_prepare_fb() function states that it can be
> used as the &drm_plane_helper_funcs.prepare_fb hook. But we have
> our own hook function which is called rcar_du_vsp_plane_prepare_fb().
> Therefore, I was not sure if it is correct to use drm_gem_fb_prepare_fb()
> inside our hook function.
>
> I will use it in the second version nevertheless.
>
>>
>> >  static int rcar_du_vsp_plane_prepare_fb(struct drm_plane *plane,
>> >                                     struct drm_plane_state *state)
>> >  {
>> > @@ -237,6 +255,8 @@ static int rcar_du_vsp_plane_prepare_fb(struct
>> drm_plane
>> > *plane, }
>> >     }
>> >
>> > +   rcar_du_vsp_set_fence_for_plane(state);
>> > +
>> >     return 0;
>> >
>> >  fail:
>>
>> --
>> Regards,
>>
>> Laurent Pinchart
>>
>>
>
> Best Regards,
>
> Emre Ucan
>
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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