[PATCH v3 2/2] drm/i915/uapi: expose GTT alignment

[Jordan Justen]

Acked-by: Jordan Justen <jordan.l.justen at intel.com>

On 2022-10-04 04:49:15, Matthew Auld wrote:
> On some platforms we potentially have different alignment restrictions
> depending on the memory type. We also now have different alignment
> restrictions for the same region across different kernel versions.
> Extend the region query to return the minimum required GTT alignment.
> 
> Testcase: igt at gem_create@create-ext-placement-alignment
> Testcase: igt at i915_query@query-regions-sanity-check
> Suggested-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> Cc: Michal Mrozek <michal.mrozek at intel.com>
> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> Cc: Stuart Summers <stuart.summers at intel.com>
> Cc: Jordan Justen <jordan.l.justen at intel.com>
> Cc: Yang A Shi <yang.a.shi at intel.com>
> Cc: Nirmoy Das <nirmoy.das at intel.com>
> Cc: Niranjana Vishwanathapura <niranjana.vishwanathapura at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_query.c |  1 +
>  include/uapi/drm/i915_drm.h       | 29 +++++++++++++++++++++++++++--
>  2 files changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
> index 6ec9c9fb7b0d..111377f210ed 100644
> --- a/drivers/gpu/drm/i915/i915_query.c
> +++ b/drivers/gpu/drm/i915/i915_query.c
> @@ -498,6 +498,7 @@ static int query_memregion_info(struct drm_i915_private *i915,
>                 info.region.memory_class = mr->type;
>                 info.region.memory_instance = mr->instance;
>                 info.probed_size = mr->total;
> +               info.gtt_alignment = mr->min_page_size;
>  
>                 if (mr->type == INTEL_MEMORY_LOCAL)
>                         info.probed_cpu_visible_size = mr->io_size;
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 08d69e36fb66..2e613109356b 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -3346,8 +3346,33 @@ struct drm_i915_memory_region_info {
>         /** @region: The class:instance pair encoding */
>         struct drm_i915_gem_memory_class_instance region;
>  
> -       /** @rsvd0: MBZ */
> -       __u32 rsvd0;
> +       union {
> +               /** @rsvd0: MBZ */
> +               __u32 rsvd0;
> +               /**
> +                * @gtt_alignment:
> +                *
> +                * The minimum required GTT alignment for this type of memory.
> +                * When allocating a GTT address it must be aligned to this
> +                * value or larger. On some platforms the kernel might opt to
> +                * using 64K pages for I915_MEMORY_CLASS_DEVICE, where 64K GTT
> +                * pages can then be used if we also use 64K GTT alignment.
> +                *
> +                * NOTE: If this is zero then this must be an older
> +                * kernel which lacks support for this field.
> +                *
> +                * Side note: For larger objects (especially for
> +                * I915_MEMORY_CLASS_DEVICE), like 2M+ in size, userspace should
> +                * consider potentially bumping the GTT alignment to say 2M,
> +                * which could potentially increase the likelihood of the kernel
> +                * being able to utilise 2M GTT pages underneath, if the layout
> +                * of the physical pages allows it.  On some configurations we
> +                * can then also use a more efficient page-table layout, if we
> +                * can't use the more desirable 2M GTT page, so long as we know
> +                * that the entire page-table will be used by this object.
> +                */
> +               __u32 gtt_alignment;
> +       };
>  
>         /**
>          * @probed_size: Memory probed by the driver
> -- 
> 2.37.3
>