Re: [Intel-gfx] [PATCH 18/23] drm/i915: Shrink the size of intel_remapped_plane_info struct

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Mar 11, 2021 at 12:17:31AM +0200, Imre Deak wrote:
> Save some place in the GTT VMAs by using a u16 instead of unsigned int
> to store the view dimensions. The maximum FB stride is 256kB which is
> 4096 tiles in the worst case (yf-tiles), the maximum FB height is 16k
> pixels, which is 2048 tiles in the worst case (x-tiles).

Actually I think the worst case for height is remapping linear fbs
since we more or less treat it as 4kx1 tiles. But 16k is still< 64k
so should be all good.

Integer promotion stuff/etc. is what worried me the most here, but
looks like rotate_pages()/remap_pages() at least gets everything
passed in as unsigned int, so we're not in danger of sign bit
shenanigans there at least.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> 
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_fb.c | 15 ++++++++++++---
>  drivers/gpu/drm/i915/i915_vma_types.h   | 12 ++++++++----
>  2 files changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fb.c b/drivers/gpu/drm/i915/display/intel_fb.c
> index 16a1b5c922bb..51c56f0a4a99 100644
> --- a/drivers/gpu/drm/i915/display/intel_fb.c
> +++ b/drivers/gpu/drm/i915/display/intel_fb.c
> @@ -619,13 +619,22 @@ static u32 calc_plane_remap_info(const struct intel_framebuffer *fb, int color_p
>  	unsigned int tile_width = dims->tile_width;
>  	unsigned int tile_height = dims->tile_height;
>  	unsigned int tile_size = intel_tile_size(i915);
> +	unsigned int stride_tiles = plane_view_stride_tiles(fb, color_plane, dims);
> +	unsigned int width_tiles = DIV_ROUND_UP(x + dims->width, dims->tile_width);
> +	unsigned int height_tiles = plane_view_tile_rows(fb, color_plane, dims, y);
>  	unsigned int pitch_tiles;
>  	struct drm_rect r;
>  
> +	drm_WARN_ON(&i915->drm,
> +		    overflows_type(obj_offset, gtt_remap_info->offset) ||
> +		    overflows_type(stride_tiles, gtt_remap_info->stride) ||
> +		    overflows_type(width_tiles, gtt_remap_info->width) ||
> +		    overflows_type(height_tiles, gtt_remap_info->height));
> +
>  	gtt_remap_info->offset = obj_offset;
> -	gtt_remap_info->width = DIV_ROUND_UP(x + dims->width, dims->tile_width);
> -	gtt_remap_info->height = plane_view_tile_rows(fb, color_plane, dims, y);
> -	gtt_remap_info->stride = plane_view_stride_tiles(fb, color_plane, dims);
> +	gtt_remap_info->stride = stride_tiles;
> +	gtt_remap_info->width = width_tiles;
> +	gtt_remap_info->height = height_tiles;
>  
>  	if (view_type == I915_GGTT_VIEW_ROTATED) {
>  		/* rotate the x/y offsets to match the GTT view */
> diff --git a/drivers/gpu/drm/i915/i915_vma_types.h b/drivers/gpu/drm/i915/i915_vma_types.h
> index f5cb848b7a7e..358b4306fc00 100644
> --- a/drivers/gpu/drm/i915/i915_vma_types.h
> +++ b/drivers/gpu/drm/i915/i915_vma_types.h
> @@ -97,12 +97,16 @@ enum i915_cache_level;
>  
>  struct intel_remapped_plane_info {
>  	/* in gtt pages */
> -	unsigned int width, height, stride, offset;
> +	u32 offset;
> +	u16 width;
> +	u16 height;
> +	u16 stride;
> +	u16 unused_mbz;
>  } __packed;
>  
>  struct intel_remapped_info {
>  	struct intel_remapped_plane_info plane[2];
> -	unsigned int unused_mbz;
> +	u32 unused_mbz;
>  } __packed;
>  
>  struct intel_rotation_info {
> @@ -123,9 +127,9 @@ enum i915_ggtt_view_type {
>  
>  static inline void assert_i915_gem_gtt_types(void)
>  {
> -	BUILD_BUG_ON(sizeof(struct intel_rotation_info) != 8*sizeof(unsigned int));
> +	BUILD_BUG_ON(sizeof(struct intel_rotation_info) != 2 * sizeof(u32) + 8 * sizeof(u16));
>  	BUILD_BUG_ON(sizeof(struct intel_partial_info) != sizeof(u64) + sizeof(unsigned int));
> -	BUILD_BUG_ON(sizeof(struct intel_remapped_info) != 9*sizeof(unsigned int));
> +	BUILD_BUG_ON(sizeof(struct intel_remapped_info) != 3 * sizeof(u32) + 8 * sizeof(u16));
>  
>  	/* Check that rotation/remapped shares offsets for simplicity */
>  	BUILD_BUG_ON(offsetof(struct intel_remapped_info, plane[0]) !=
> -- 
> 2.25.1
> 
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-- 
Ville Syrjälä
Intel
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