Re: [PATCH 1/5] drm/i915/ttm: Add I915_BO_PREALLOC

[Andrzej Hajda <andrzej.hajda@xxxxxxxxx>]

On 04.04.2023 16:30, Nirmoy Das wrote:
> Add a mechanism to keep existing data when creating
> a ttm object with I915_BO_ALLOC_USER flag.
>
> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
> Cc: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Imre Deak <imre.deak@xxxxxxxxx>
> Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
> ---
>   drivers/gpu/drm/i915/gem/i915_gem_object_types.h | 15 +++++++++++----
>   drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c     |  5 +++--
>   2 files changed, 14 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> index 5dcbbef31d44..830c11431ee8 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> @@ -328,6 +328,12 @@ struct drm_i915_gem_object {
>    */
>   #define I915_BO_ALLOC_GPU_ONLY	  BIT(6)
>   #define I915_BO_ALLOC_CCS_AUX	  BIT(7)
> +/*
> + * Object is allowed to retain its initial data and will not be cleared on first
> + * access if used along with I915_BO_ALLOC_USER. This is mainly to keep
> + * preallocated framebuffer data intact while transitioning it to i915drmfb.
> + */
> +#define I915_BO_PREALLOC	  BIT(8)
>   #define I915_BO_ALLOC_FLAGS (I915_BO_ALLOC_CONTIGUOUS | \
>   			     I915_BO_ALLOC_VOLATILE | \
>   			     I915_BO_ALLOC_CPU_CLEAR | \
> @@ -335,10 +341,11 @@ struct drm_i915_gem_object {
>   			     I915_BO_ALLOC_PM_VOLATILE | \
>   			     I915_BO_ALLOC_PM_EARLY | \
>   			     I915_BO_ALLOC_GPU_ONLY | \
> -			     I915_BO_ALLOC_CCS_AUX)
> -#define I915_BO_READONLY          BIT(8)
> -#define I915_TILING_QUIRK_BIT     9 /* unknown swizzling; do not release! */
> -#define I915_BO_PROTECTED         BIT(10)
> +			     I915_BO_ALLOC_CCS_AUX | \
> +			     I915_BO_PREALLOC)
> +#define I915_BO_READONLY          BIT(9)
> +#define I915_TILING_QUIRK_BIT     10 /* unknown swizzling; do not release! */
> +#define I915_BO_PROTECTED         BIT(11)
>   	/**
>   	 * @mem_flags - Mutable placement-related flags
>   	 *
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> index dd188dfcc423..69eb20ed4d47 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm_move.c
> @@ -576,7 +576,7 @@ int i915_ttm_move(struct ttm_buffer_object *bo, bool evict,
>   	struct dma_fence *migration_fence = NULL;
>   	struct ttm_tt *ttm = bo->ttm;
>   	struct i915_refct_sgt *dst_rsgt;
> -	bool clear;
> +	bool clear, prealloc_bo;
>   	int ret;
>   
>   	if (GEM_WARN_ON(i915_ttm_is_ghost_object(bo))) {
> @@ -632,7 +632,8 @@ int i915_ttm_move(struct ttm_buffer_object *bo, bool evict,
>   		return PTR_ERR(dst_rsgt);
>   
>   	clear = !i915_ttm_cpu_maps_iomem(bo->resource) && (!ttm || !ttm_tt_is_populated(ttm));
> -	if (!(clear && ttm && !(ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC))) {
> +	prealloc_bo = obj->flags & I915_BO_PREALLOC;
> +	if (!(clear && ttm && !((ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) && !prealloc_bo))) {

This looks like school exercise for complicated usage of logical 
operators, and I have problem with understanding this :)
Couldn't this be somehow simplified?

Anyway as the patch just reuses existing code:
Reviewed-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>

Regards
Andrzej


>   		struct i915_deps deps;
>   
>   		i915_deps_init(&deps, GFP_KERNEL | __GFP_NORETRY | __GFP_NOWARN);