[Intel-gfx] [PATCH] drm/i915: Make sure DC writes are coherent on flush.

[Jani Nikula]

On Thu, 14 Jan 2016, Francisco Jerez <currojerez at riseup.net> wrote:
> We need to set the DC FLUSH PIPE_CONTROL bit on Gen7+ to guarantee
> that writes performed via the HDC are visible in memory.  Fixes an
> intermittent failure in a Piglit test that writes to a BO from a
> shader using GL atomic counters (implemented as HDC untyped atomics)
> and then expects the memory to read back the same value after mapping
> it on the CPU.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91298
> Tested-by: Mark Janes <mark.a.janes at intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>

Should this be backported to stable kernels? Is this a regression, or
has it always been broken?

BR,
Jani.


> ---
>  drivers/gpu/drm/i915/intel_lrc.c        | 1 +
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 2 ++
>  2 files changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index ab344e0..02213c6 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1735,6 +1735,7 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
>  	if (flush_domains) {
>  		flags |= PIPE_CONTROL_RENDER_TARGET_CACHE_FLUSH;
>  		flags |= PIPE_CONTROL_DEPTH_CACHE_FLUSH;
> +		flags |= PIPE_CONTROL_DC_FLUSH_ENABLE;
>  		flags |= PIPE_CONTROL_FLUSH_ENABLE;
>  	}
>  
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 4060acf..8cd8aab 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -331,6 +331,7 @@ gen7_render_ring_flush(struct drm_i915_gem_request *req,
>  	if (flush_domains) {
>  		flags |= PIPE_CONTROL_RENDER_TARGET_CACHE_FLUSH;
>  		flags |= PIPE_CONTROL_DEPTH_CACHE_FLUSH;
> +		flags |= PIPE_CONTROL_DC_FLUSH_ENABLE;
>  		flags |= PIPE_CONTROL_FLUSH_ENABLE;
>  	}
>  	if (invalidate_domains) {
> @@ -403,6 +404,7 @@ gen8_render_ring_flush(struct drm_i915_gem_request *req,
>  	if (flush_domains) {
>  		flags |= PIPE_CONTROL_RENDER_TARGET_CACHE_FLUSH;
>  		flags |= PIPE_CONTROL_DEPTH_CACHE_FLUSH;
> +		flags |= PIPE_CONTROL_DC_FLUSH_ENABLE;
>  		flags |= PIPE_CONTROL_FLUSH_ENABLE;
>  	}
>  	if (invalidate_domains) {

-- 
Jani Nikula, Intel Open Source Technology Center