Re: [PATCH v3] drm/xe: Align all 64k VRAM buffers physically when multiple of 64k.

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Aug 22, 2024 at 04:23:46PM +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,

I don't see this happening in the code anymore. Where's the check for
the scanout flag? What am I missing?

> we take the safe route and force the physical alignment of 64k pages.

If I had understood it correctly, this is one of the things that
Jose was asking us to avoid since the alignment on the address
was not actually needed. But I might have understood him.

Cc: José Roberto de Souza <jose.souza@intel.com>

> 
> 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.
> 
> This is a slightly different approach from my previous patch. Instead
> of requiring a scanout flag at FB creation, we now make all buffers of
> the right size physically aligned correctly, so no change from userspace
> is needed.

could be a v3: mark and a more imperative language. Something like:

v3: Instead of requiring scanout flag at FB creation, we now make...

> 
> It will be interesting to see if it affects performance in any way,
> could potentially even improve things with 64k PTE's.
> 
> Inspired by Zbigniews patch.

This 2 phrases above should probably be added below the '---' mark,
and not as part of the commit message.

> 
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Co-developed-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>

Zbigniew, we need your signoff-by here as well if this is the case.

> 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>
> ---
> Changes since previous version:
> - Drop DISPLAY_NEED64K.
> - Hardcode check for I915_FORMAT_MOD_4_TILED_BMG_CCS, only one affected.

I like these 2 changes for a cleaner code.

> 
>  drivers/gpu/drm/xe/display/intel_fb_bo.c |  5 +++++
>  drivers/gpu/drm/xe/xe_bo.c               | 10 ++++++++++
>  drivers/gpu/drm/xe/xe_vm.c               |  3 ++-
>  3 files changed, 17 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..de613325e0bb0 100644
> --- a/drivers/gpu/drm/xe/display/intel_fb_bo.c
> +++ b/drivers/gpu/drm/xe/display/intel_fb_bo.c
> @@ -28,6 +29,10 @@ int intel_fb_bo_framebuffer_init(struct intel_framebuffer *intel_fb,
>  	struct xe_device *xe = to_xe_device(bo->ttm.base.dev);
>  	int ret;
>  
> +	if (XE_IOCTL_DBG(xe, mode_cmd->modifier[0] == I915_FORMAT_MOD_4_TILED_BMG_CCS &&
> +			     !(bo->flags & XE_BO_FLAG_NEEDS_64K)))

parenthesis misallignment

> +		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 6ed0e19552159..dd54cbc14e9d8 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -2019,6 +2019,16 @@ int xe_gem_create_ioctl(struct drm_device *dev, void *data,
>  
>  	bo_flags |= args->placement << (ffs(XE_BO_FLAG_SYSTEM) - 1);
>  
> +	/*
> +	 * Lets see what happens if we simply align any buffer that's
> +	 * a multiple of 64k to 64k in places where it's not officially
> +	 * needed.
> +	 */
> +	if ((bo_flags & XE_BO_FLAG_VRAM_MASK) &&
> +	    !(xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K) &&
> +	    !(args->size % SZ_64K))

shouldn't we be checking for the scanout here as well?

> +		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 d1bfd0b6e9558..af215f6d6588b 100644
> --- a/drivers/gpu/drm/xe/xe_vm.c
> +++ b/drivers/gpu/drm/xe/xe_vm.c
> @@ -2878,7 +2878,8 @@ 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) {
> +	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) ||
> -- 
> 2.45.2
>