Re: [PATCH] drm/i915: Use LRI to update the semaphore registers

[Ben Widawsky <ben@bwidawsk.net>]

On Wed, 14 Nov 2012 09:15:14 +0000
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> The bspec was recently updated to remove the ability to update the
> semaphore using the MI_SEMAPHORE_BOX command, the ability to wait upon
> the semaphore value remained. Instead the advice is to update the
> register using the MI_LOAD_REGISTER_IMM command. In cursory testing,
> semaphores continue to function - the question is whether this fixes
> some of the deadlocks where the semaphore registers contained stale
> values?
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel J Blueman <daniel@quora.org>
Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/intel_ringbuffer.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index ee4abc5..dd2e7db 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -554,12 +554,9 @@ update_mboxes(struct intel_ring_buffer *ring,
>  	    u32 seqno,
>  	    u32 mmio_offset)
>  {
> -	intel_ring_emit(ring, MI_SEMAPHORE_MBOX |
> -			      MI_SEMAPHORE_GLOBAL_GTT |
> -			      MI_SEMAPHORE_REGISTER |
> -			      MI_SEMAPHORE_UPDATE);
> -	intel_ring_emit(ring, seqno);
> +	intel_ring_emit(ring, MI_LOAD_REGISTER_IMM(1));
>  	intel_ring_emit(ring, mmio_offset);
> +	intel_ring_emit(ring, seqno);
>  }
>  
>  /**



-- 
Ben Widawsky, Intel Open Source Technology Center