[Intel-gfx] [RFC] drm/i915: check that rpm ref is held when writing to ringbuf in stolen mem

[Chris Wilson]

On Wed, Jan 27, 2016 at 08:55:40AM +0000, daniele.ceraolospurio at intel.com wrote:
> From: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> 
> While running some tests on the scheduler patches with rpm enabled I
> came across a corruption in the ringbuffer, which was root-caused to
> the GPU being suspended while commands were being emitted to the
> ringbuffer. The access to memory was failing because the GPU needs to
> be awake when accessing stolen memory (where my ringbuffer was located).
> Since we have this constraint it looks like a sensible idea to check that
> we hold a refcount when we emit commands.
> 
> Cc: John Harrison <John.C.Harrison at Intel.com>
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> ---
>  drivers/gpu/drm/i915/intel_lrc.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 3761eaf..f9e8d74 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1105,6 +1105,11 @@ int intel_logical_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
>  	if (ret)
>  		return ret;
>  
> +	// If the ringbuffer is in stolen memory we need to be sure that the
> +	// gpu is awake before writing to it
> +	if (req->ringbuf->obj->stolen && num_dwords > 0)
> +		assert_rpm_wakelock_held(dev_priv);

The assertion you want is that when iomapping through the GTT that we
hold a wakeref.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre