Re: [PATCH] drm/i915: correctly order the ring init sequence

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 07 Aug 2012, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> We may only start to set up the new register values after having
> confirmed that the ring is truely off. Otherwise the hw might lose the
> newly written register values. This is caught later on in the init
> sequence, when we check whether the register writes have stuck.

With or without (up to you) the comment clarification discussed in IRC,

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


>
> Cc: stable@vger.kernel.org
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50522
> Tested-by: Yang Guang <guang.a.yang@intel.com>
> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index bf0195a..5b19917 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -289,8 +289,6 @@ static int init_ring_common(struct intel_ring_buffer *ring)
>  	I915_WRITE_HEAD(ring, 0);
>  	ring->write_tail(ring, 0);
>  
> -	/* Initialize the ring. */
> -	I915_WRITE_START(ring, obj->gtt_offset);
>  	head = I915_READ_HEAD(ring) & HEAD_ADDR;
>  
>  	/* G45 ring initialization fails to reset head to zero */
> @@ -316,6 +314,10 @@ static int init_ring_common(struct intel_ring_buffer *ring)
>  		}
>  	}
>  
> +	/* Initialize the ring. This must happen _after_ we have confirmed that
> +	 * the ring is off (with the above head == 0 check), otherwise the hw
> +	 * might lose the new ring register values. */
> +	I915_WRITE_START(ring, obj->gtt_offset);
>  	I915_WRITE_CTL(ring,
>  			((ring->size - PAGE_SIZE) & RING_NR_PAGES)
>  			| RING_VALID);
> -- 
> 1.7.10.4
>
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