Re: [PATCH v5 1/2] drm/xe: Align all VRAM scanout buffers to 64k physical pages when needed.

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

On Mon, 2024-08-26 at 11:50 +0200, Maarten Lankhorst wrote:
> For CCS formats on affected platforms, CCS can be used freely, but
> display engine requires a multiple of 64k physical pages. No other
> changes are needed.
> 
> At the BO creation time we don't know if the BO will be used for CCS
> or not. If the scanout flag is set, and the BO is a multiple of 64k,
> we take the safe route and force the physical alignment of 64k pages.
> 
> If the BO is not a multiple of 64k, or the scanout flag was not set
> at BO creation, we reject it for usage as CCS in display. The
> physical
> pages are likely not aligned correctly, and this will cause
> corruption
> when used as FB.
> 
> The scanout flag and size being a multiple of 64k are used together
> to enforce 64k physical placement.
> 
> VM_BIND is completely unaffected, mappings to a VM can still be
> aligned
> to 4k, just like for normal buffers.
> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Co-developed-by: Zbigniew Kempczyński
> <zbigniew.kempczynski@intel.com>
> Cc: Matthew Auld <matthew.auld@intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Juha-Pekka Heikkilä <juha-pekka.heikkila@intel.com>
> ---
>  drivers/gpu/drm/xe/display/intel_fb_bo.c |  5 +++++
>  drivers/gpu/drm/xe/xe_bo.c               |  7 +++++++
>  drivers/gpu/drm/xe/xe_vm.c               | 11 ++++++++++-
>  3 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/display/intel_fb_bo.c
> b/drivers/gpu/drm/xe/display/intel_fb_bo.c
> index f835492f73fb4..6775c2557b9df 100644
> --- a/drivers/gpu/drm/xe/display/intel_fb_bo.c
> +++ b/drivers/gpu/drm/xe/display/intel_fb_bo.c
> @@ -28,6 +28,11 @@ int intel_fb_bo_framebuffer_init(struct
> intel_framebuffer *intel_fb,
>  	struct xe_device *xe = to_xe_device(bo->ttm.base.dev);
>  	int ret;
>  
> +	/* Only this specific format is affected, and it's only
> available on VRAM */

A first time reader would wonder "Affected by what". Could we rephrase
like "This specific format, only available with DGFX needs .." or
something similar self-contained?

> +	if (XE_IOCTL_DBG(xe, mode_cmd->modifier[0] ==
> I915_FORMAT_MOD_4_TILED_BMG_CCS &&
> +			     !(bo->flags & XE_BO_FLAG_NEEDS_64K)))
> +		return -EINVAL;
> +
>  	xe_bo_get(bo);
>  
>  	ret = ttm_bo_reserve(&bo->ttm, true, false, NULL);
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index cbe7bf098970f..41297b5797173 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -2019,6 +2019,13 @@ int xe_gem_create_ioctl(struct drm_device
> *dev, void *data,
>  
>  	bo_flags |= args->placement << (ffs(XE_BO_FLAG_SYSTEM) - 1);
>  
> +	/* CCS formats need physical placement at a 64K alignment in
> VRAM. */
> +	if ((bo_flags & XE_BO_FLAG_VRAM_MASK) &&
> +	    (bo_flags & XE_BO_FLAG_SCANOUT) &&
> +	    !(xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K) &&
> +	    !(args->size % SZ_64K))

This might probably fail on 32-bit compiles? Can we use the IS_ALIGNED
macro?


> +		bo_flags |= XE_BO_FLAG_NEEDS_64K;
> +
>  	if (args->flags & DRM_XE_GEM_CREATE_FLAG_NEEDS_VISIBLE_VRAM)
> {
>  		if (XE_IOCTL_DBG(xe, !(bo_flags &
> XE_BO_FLAG_VRAM_MASK)))
>  			return -EINVAL;
> diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
> index 4cc13eddb6b32..3eb76d874eb28 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -2878,7 +2878,16 @@ static int xe_vm_bind_ioctl_validate_bo(struct
> xe_device *xe, struct xe_bo *bo,
>  		return -EINVAL;
>  	}
>  
> -	if (bo->flags & XE_BO_FLAG_INTERNAL_64K) {
> +	/*
> +	 * Some platforms require 64k VM_BIND alignment,
> +	 * specifically those with XE_VRAM_FLAGS_NEED64K.
> +	 *
> +	 * Other platforms may have BO's set to 64k physical
> placement,
> +	 * but can be mapped at 4k offsets anyway. This check is
> only
> +	 * there for the former case.
> +	 */
> +	if ((bo->flags & XE_BO_FLAG_INTERNAL_64K) &&
> +	    (xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K)) {
>  		if (XE_IOCTL_DBG(xe, obj_offset &
>  				 XE_64K_PAGE_MASK) ||
>  		    XE_IOCTL_DBG(xe, addr & XE_64K_PAGE_MASK) ||

Otherwise LGTM.
/Thomas