[Intel-gfx] [PATCH] drm/i915: Add support for resetting the SO write pointers on gen7.

[Eugeni Dodonov]

On Thu, Dec 29, 2011 at 23:52, Eric Anholt <eric at anholt.net> wrote:

> These registers are automatically incremented by the hardware during
> transform feedback to track where the next streamed vertex output
> should go.  Unlike the previous generation, which had a packet for
> setting the corresponding registers to a defined value, gen7 only has
> MI_LOAD_REGISTER_IMM to do so.  That's a secure packet (since it loads
> an arbitrary register), so we need to do it from the kernel, and it
> needs to be settable atomically with the batchbuffer execution so that
> two clients doing transform feedback don't stomp on each others'
> state.
>
> Instead of building a more complicated interface involcing setting the
> registers to a specific value, just set them to 0 when asked and
> userland can tweak its pointers accordingly.
>
> Signed-off-by: Eric Anholt <eric at anholt.net>
>
---
>  drivers/gpu/drm/i915/i915_dma.c            |    3 ++
>  drivers/gpu/drm/i915/i915_gem_execbuffer.c |   31
> ++++++++++++++++++++++++++++
>  drivers/gpu/drm/i915/i915_reg.h            |    6 +++++
>  include/drm/i915_drm.h                     |    4 +++
>  4 files changed, 44 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_dma.c
> b/drivers/gpu/drm/i915/i915_dma.c
> index a9ae374..1add685 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -781,6 +781,9 @@ static int i915_getparam(struct drm_device *dev, void
> *data,
>        case I915_PARAM_HAS_RELAXED_DELTA:
>                value = 1;
>                break;
> +       case I915_PARAM_HAS_GEN7_SOL_RESET:
> +               value = 1;
>

Wouldn't it be better to have:
                   value = IS_GEN7(dev);

as it is gen7+-specific item. This way, userspace could check for this
support early, and avoid setting the flag on the batchbuffer in vain on
pre-gen7 architectures.

Either way, it will work, so:

Reviewed-by: Eugeni Dodonov <eugeni.dodonov at intel.com>

-- 
Eugeni Dodonov
<http://eugeni.dodonov.net/>
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