Re: [Intel-gfx] [PATCH v2 12/15] drm/i915/create: apply ALLOC_GPU_ONLY by default

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 2/10/22 13:13, Matthew Auld wrote:
> Starting from DG2+, when dealing with LMEM, we assume that by default
> all userspace allocations should be placed in the non-mappable portion
> of LMEM.  Note that dumb buffers are not included here, since these are
> not "GPU accelerated" and likely need CPU access.
>
> In a later patch userspace will be able to provide a hint if CPU access
> to the buffer is needed.
>
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_create.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> index 9402d4bf4ffc..cc9ddb943f96 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
> @@ -424,6 +424,15 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
>   		ext_data.n_placements = 1;
>   	}
>   
> +	/*
> +	 * TODO: add a userspace hint to force CPU_ACCESS for the object, which
> +	 * can override this.
> +	 */
> +	if (!IS_DG1(i915) && (ext_data.n_placements > 1 ||
> +			      ext_data.placements[0]->type !=
> +			      INTEL_MEMORY_SYSTEM))
> +		ext_data.flags |= I915_BO_ALLOC_GPU_ONLY;
> +

WRT previous review comment here, it would be easier to follow if the bo 
was marked as a GPU only buffer regardless. Then for example capture and 
other functions where it actually matters can choose to take action 
based on, for example, whether the BAR is restricted or not?

/Thomas



>   	obj = __i915_gem_object_create_user_ext(i915, args->size,
>   						ext_data.placements,
>   						ext_data.n_placements,