Re: [PATCH v2 23/25] drm/xe: Compute dumb-buffer sizes with drm_mode_size_dumb()

[Matthew Auld <matthew.auld@intel.com>]

On 09/01/2025 14:57, Thomas Zimmermann wrote:
> Call drm_mode_size_dumb() to compute dumb-buffer scanline pitch
> and buffer size. Align the pitch to a multiple of 8. Align the
> buffer size according to hardware requirements.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> ---
>   drivers/gpu/drm/xe/xe_bo.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index e6c896ad5602..d75e3c39ab14 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -8,6 +8,7 @@
>   #include <linux/dma-buf.h>
>   
>   #include <drm/drm_drv.h>
> +#include <drm/drm_dumb_buffers.h>
>   #include <drm/drm_gem_ttm_helper.h>
>   #include <drm/drm_managed.h>
>   #include <drm/ttm/ttm_device.h>
> @@ -2535,14 +2536,13 @@ int xe_bo_dumb_create(struct drm_file *file_priv,
>   	struct xe_device *xe = to_xe_device(dev);
>   	struct xe_bo *bo;
>   	uint32_t handle;
> -	int cpp = DIV_ROUND_UP(args->bpp, 8);
>   	int err;
>   	u32 page_size = max_t(u32, PAGE_SIZE,
>   		xe->info.vram_flags & XE_VRAM_FLAGS_NEED64K ? SZ_64K : SZ_4K);
>   
> -	args->pitch = ALIGN(args->width * cpp, 64);
> -	args->size = ALIGN(mul_u32_u32(args->pitch, args->height),
> -			   page_size);
> +	err = drm_mode_size_dumb(dev, args, SZ_64, page_size);

AFAICT this looks to change the behaviour, where u64 size was 
technically possible and was allowed given that args->size is u64, but 
this helper is limiting the size to u32. Is that intentional? If so, we 
should probably make that clear in the commit message.

> +	if (err)
> +		return err;
>   
>   	bo = xe_bo_create_user(xe, NULL, NULL, args->size,
>   			       DRM_XE_GEM_CPU_CACHING_WC,