[Intel-gfx] [PATCH v2 1/2] drm/i915: drop one bit on the hw_id when using guc

[Chris Wilson]

Quoting Lionel Landwerlin (2018-06-01 10:52:14)
> We currently using GuC as a proxy to the hardware. When Guc is used in
> such mode, it consumes the bit 20 of the hw_id to indicate that the
> workload was submitted by proxy.
> 
> So far we probably haven't seen the issue because we need to allocate
> 1048576+ contexts to hit this issue. Still, we should avoid allocating
> the hw_id on that bit and restriction to bits [0:19] (i.e 20bits
> instead of 21).
> 
> v2: Leave the max hw_id computation in i915_gem_context.c (Michel)
> 
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> BSpec: 1237
> ---
>  drivers/gpu/drm/i915/i915_drv.h         |  1 +
>  drivers/gpu/drm/i915/i915_gem_context.c | 14 +++++++++++---
>  drivers/gpu/drm/i915/intel_lrc.c        |  2 +-
>  3 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 38157df6ff5c..7088a1c3b6ad 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1841,6 +1841,7 @@ struct drm_i915_private {
>                  */
>                 struct ida hw_ida;
>  #define MAX_CONTEXT_HW_ID (1<<21) /* exclusive */
> +#define MAX_GUC_CONTEXT_HW_ID (1<<20) /* exclusive */
>  #define GEN11_MAX_CONTEXT_HW_ID (1<<11) /* exclusive */
>         } contexts;
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index 81f086397d10..fa732592e221 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -208,10 +208,18 @@ static int assign_hw_id(struct drm_i915_private *dev_priv, unsigned *out)
>         int ret;
>         unsigned int max;
>  
> -       if (INTEL_GEN(dev_priv) >= 11)
> +       if (INTEL_GEN(dev_priv) >= 11) {
>                 max = GEN11_MAX_CONTEXT_HW_ID;
> -       else
> -               max = MAX_CONTEXT_HW_ID;
> +       } else {
> +               /*
> +                * When using GuC in proxy submission, GuC consumes the
> +                * highest bit in the context id to indicate proxy submission.
> +                */
> +               max = USES_GUC_SUBMISSION(dev_priv) ?
> +                       MAX_GUC_CONTEXT_HW_ID :
> +                       MAX_CONTEXT_HW_ID;

I'm just going to say mixing if() and ternary ?: isn't great style. 

Acked-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris