Re: [PATCH v3] drm/i915: check that rpm ref is held when accessing ringbuf in stolen mem

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Jan 27, 2016 at 03:43:49PM +0000, daniele.ceraolospurio@intel.com wrote:
> From: Daniele Ceraolo Spurio <daniele.ceraolospurio@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 access the rungbuffer.
> 
> v2: move the check from ring_begin to ringbuffer iomap time (Chris)
> v3: update comment (Chris)
> 
> Cc: John Harrison <John.C.Harrison@Intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 6f5b511..133321a 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2119,6 +2119,9 @@ int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
>  			return ret;
>  		}
>  
> +		/* Access through the GTT requires the device to be awake. */
> +		assert_rpm_wakelock_held(dev_priv);
> +

Hmm. This function doesn't actually acces the ring buffer, so it's a bit
odd to see this here.

>  		ringbuf->virtual_start = ioremap_wc(dev_priv->gtt.mappable_base +
>  						    i915_gem_obj_ggtt_offset(obj), ringbuf->size);
>  		if (ringbuf->virtual_start == NULL) {
> -- 
> 1.9.1
> 
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-- 
Ville Syrjälä
Intel OTC
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