[PATCH] drm/radeon: Only flush HDP cache from idle ioctl if BO is in VRAM

[Marek Olšák]

I'm afraid this won't always work and it can be a source of bugs.

Userspace doesn't have to call GEM_WAIT_IDLE before a CPU access to a
VRAM buffer. For example, consider a wait-idle request with a non-zero
timeout, which is implemented as a loop which calls GEM_BUSY. Also,
userspace can use fences (alright they are backed by 1-page-sized VRAM
buffers at the moment) and it may use real fences in the future which
are not tied to a buffer object.

If the HDP flush isn't allowed in userspace IBs, I think we will have
to expose it as an ioctl and call it explicitly from userspace.

Marek

On Fri, Aug 1, 2014 at 10:22 AM, Michel Dänzer <michel at daenzer.net> wrote:
> From: Michel Dänzer <michel.daenzer at amd.com>
>
> The HDP cache only applies to CPU access to VRAM.
>
> Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
> ---
>  drivers/gpu/drm/radeon/radeon_gem.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_gem.c b/drivers/gpu/drm/radeon/radeon_gem.c
> index a350cf9..8f2cb58 100644
> --- a/drivers/gpu/drm/radeon/radeon_gem.c
> +++ b/drivers/gpu/drm/radeon/radeon_gem.c
> @@ -359,15 +359,17 @@ int radeon_gem_wait_idle_ioctl(struct drm_device *dev, void *data,
>         struct drm_gem_object *gobj;
>         struct radeon_bo *robj;
>         int r;
> +       uint32_t cur_placement = 0;
>
>         gobj = drm_gem_object_lookup(dev, filp, args->handle);
>         if (gobj == NULL) {
>                 return -ENOENT;
>         }
>         robj = gem_to_radeon_bo(gobj);
> -       r = radeon_bo_wait(robj, NULL, false);
> +       r = radeon_bo_wait(robj, &cur_placement, false);
>         /* Flush HDP cache via MMIO if necessary */
> -       if (rdev->asic->mmio_hdp_flush)
> +       if (rdev->asic->mmio_hdp_flush &&
> +           radeon_mem_type_to_domain(cur_placement) == RADEON_GEM_DOMAIN_VRAM)
>                 robj->rdev->asic->mmio_hdp_flush(rdev);
>         drm_gem_object_unreference_unlocked(gobj);
>         r = radeon_gem_handle_lockup(rdev, r);
> --
> 2.0.1
>
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