[Intel-gfx] [PATCH] drm/i915/guc: Reserve the upper end of the Global GTT for the GuC

[Michal Wajdeczko]

On Wed, Dec 21, 2016 at 02:11:26PM +0000, Chris Wilson wrote:
> The GuC would like to own the upper portion of the GTT for itself, so
> exclude it from our drm_mm to prevent us using it.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Michal Wajdeczko <michal.wajdeczko at intel.com>
> Cc: Arkadiusz Hiler <arkadiusz.hiler at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_gtt.c   | 5 +++++
>  drivers/gpu/drm/i915/intel_guc_fwif.h | 3 +++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 6af9311f72f5..96bc0e83286a 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -3176,6 +3176,11 @@ int i915_ggtt_probe_hw(struct drm_i915_private *dev_priv)
>  	if (ret)
>  		return ret;
>  
> +	if (HAS_GUC_SCHED(dev_priv)) {

Btw, shouldn't we also modify HAS_GUC_SCHED macro to look at i915.enable_guc_submission
instead of .has_guc ? Note that Guc may be present but disabled...

> +		ggtt->base.total -= GUC_GGTT_RESERVED_TOP;

Hmm, while unlikely, what if RESERVED_TOP is larger than detected base.total ?

> +		ggtt->mappable_end = min(ggtt->mappable_end, ggtt->base.total);
> +	}
> +
>  	if ((ggtt->base.total - 1) >> 32) {
>  		DRM_ERROR("We never expected a Global GTT with more than 32bits"
>  			  " of address space! Found %lldM!\n",
> diff --git a/drivers/gpu/drm/i915/intel_guc_fwif.h b/drivers/gpu/drm/i915/intel_guc_fwif.h
> index 3202b32b5638..3361d38ed859 100644
> --- a/drivers/gpu/drm/i915/intel_guc_fwif.h
> +++ b/drivers/gpu/drm/i915/intel_guc_fwif.h
> @@ -23,6 +23,9 @@
>  #ifndef _INTEL_GUC_FWIF_H
>  #define _INTEL_GUC_FWIF_H
>  
> +/* A small region at the top of the global GTT is reserved for use by the GuC */
> +#define GUC_GGTT_RESERVED_TOP		0x1200000

Is this region size fixed (part of Guc HW assumptions), or it can change per different FW?
If former, then maybe this macro should be moved to i915_guc_reg.h?
If latter, then maybe it is worth to explictly state that in the comment?

> +
>  #define GFXCORE_FAMILY_GEN9		12
>  #define GFXCORE_FAMILY_UNKNOWN		0x7fffffff
>  
> -- 
> 2.11.0
> 

Thanks,
Michal