On Tue, 9 Oct 2012 19:24:39 +0100
Chris Wilson <chris at chris-wilson.co.uk> wrote:
> Hopefully this will reduce a few of the missed IRQ warnings.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
> drivers/gpu/drm/i915/intel_ringbuffer.c | 8 +++++++-
> drivers/gpu/drm/i915/intel_ringbuffer.h | 2 --
> 2 files changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index e069e69..133beb6 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -704,14 +704,18 @@ gen6_ring_get_seqno(struct intel_ring_buffer *ring, bool lazy_coherency)
> /* Workaround to force correct ordering between irq and seqno writes on
> * ivb (and maybe also on snb) by reading from a CS register (like
> * ACTHD) before reading the status page. */
> - if (!lazy_coherency)
> + if (!lazy_coherency) {
> intel_ring_get_active_head(ring);
> + mb();
> + }
> return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
> }
>
> static u32
> ring_get_seqno(struct intel_ring_buffer *ring, bool lazy_coherency)
> {
> + if (!lazy_coherency)
> + mb();
> return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
> }
>
> @@ -719,6 +723,8 @@ static u32
> pc_render_get_seqno(struct intel_ring_buffer *ring, bool lazy_coherency)
> {
> struct pipe_control *pc = ring->private;
> + if (!lazy_coherency)
> + mb();
> return pc->cpu_page[0];
> }
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 2ea7a31..40b252e 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -160,8 +160,6 @@ static inline u32
> intel_read_status_page(struct intel_ring_buffer *ring,
> int reg)
> {
> - /* Ensure that the compiler doesn't optimize away the load. */
> - barrier();
> return ring->status_page.page_addr[reg];
> }
>
This looks a bit more voodoo-y. Theoretically an mb() on the CPU side
should have nothing to do with what the GPU just wrote to the status
page. It'll slow down the read a bit but shouldn't affect coherence at
all... An MMIO read from the GPU otoh should flush any stubborn DMA
buffers.
--
Jesse Barnes, Intel Open Source Technology Center
