Re: [PATCH] drm/ttm: Add a flag to allow drivers to skip clear-on-free

[Christian König <christian.koenig@xxxxxxx>]

Am 24.06.24 um 12:07 schrieb Nirmoy Das:
> Add TTM_TT_FLAG_CLEARED_ON_FREE, which DRM drivers can set before
> releasing backing stores if they want to skip clear-on-free.
>
> Cc: Matthew Auld <matthew.auld@xxxxxxxxx>
> Cc: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> Suggested-by: Christian König <christian.koenig@xxxxxxx>
> Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>

Reviewed-by: Christian König <christian.koenig@xxxxxxx>

> ---
>   drivers/gpu/drm/ttm/ttm_pool.c | 18 +++++++++++-------
>   include/drm/ttm/ttm_tt.h       |  6 +++++-
>   2 files changed, 16 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> index 6e1fd6985ffc..b78ee7524bcf 100644
> --- a/drivers/gpu/drm/ttm/ttm_pool.c
> +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> @@ -222,15 +222,18 @@ static void ttm_pool_unmap(struct ttm_pool *pool, dma_addr_t dma_addr,
>   }
>   
>   /* Give pages into a specific pool_type */
> -static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p)
> +static void ttm_pool_type_give(struct ttm_pool_type *pt, struct page *p,
> +			       bool cleared)
>   {
>   	unsigned int i, num_pages = 1 << pt->order;
>   
> -	for (i = 0; i < num_pages; ++i) {
> -		if (PageHighMem(p))
> -			clear_highpage(p + i);
> -		else
> -			clear_page(page_address(p + i));
> +	if (!cleared) {
> +		for (i = 0; i < num_pages; ++i) {
> +			if (PageHighMem(p))
> +				clear_highpage(p + i);
> +			else
> +				clear_page(page_address(p + i));
> +		}
>   	}
>   
>   	spin_lock(&pt->lock);
> @@ -394,6 +397,7 @@ static void ttm_pool_free_range(struct ttm_pool *pool, struct ttm_tt *tt,
>   				pgoff_t start_page, pgoff_t end_page)
>   {
>   	struct page **pages = &tt->pages[start_page];
> +	bool cleared = tt->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE;
>   	unsigned int order;
>   	pgoff_t i, nr;
>   
> @@ -407,7 +411,7 @@ static void ttm_pool_free_range(struct ttm_pool *pool, struct ttm_tt *tt,
>   
>   		pt = ttm_pool_select_type(pool, caching, order);
>   		if (pt)
> -			ttm_pool_type_give(pt, *pages);
> +			ttm_pool_type_give(pt, *pages, cleared);
>   		else
>   			ttm_pool_free_page(pool, caching, order, *pages);
>   	}
> diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
> index 2b9d856ff388..cfaf49de2419 100644
> --- a/include/drm/ttm/ttm_tt.h
> +++ b/include/drm/ttm/ttm_tt.h
> @@ -85,6 +85,9 @@ struct ttm_tt {
>   	 * fault handling abuses the DMA api a bit and dma_map_attrs can't be
>   	 * used to assure pgprot always matches.
>   	 *
> +	 * TTM_TT_FLAG_CLEARED_ON_FREE: Set this if a drm driver handles
> +	 * clearing backing store
> +	 *
>   	 * TTM_TT_FLAG_PRIV_POPULATED: TTM internal only. DO NOT USE. This is
>   	 * set by TTM after ttm_tt_populate() has successfully returned, and is
>   	 * then unset when TTM calls ttm_tt_unpopulate().
> @@ -94,8 +97,9 @@ struct ttm_tt {
>   #define TTM_TT_FLAG_EXTERNAL		BIT(2)
>   #define TTM_TT_FLAG_EXTERNAL_MAPPABLE	BIT(3)
>   #define TTM_TT_FLAG_DECRYPTED		BIT(4)
> +#define TTM_TT_FLAG_CLEARED_ON_FREE	BIT(5)
>   
> -#define TTM_TT_FLAG_PRIV_POPULATED	BIT(5)
> +#define TTM_TT_FLAG_PRIV_POPULATED	BIT(6)
>   	uint32_t page_flags;
>   	/** @num_pages: Number of pages in the page array. */
>   	uint32_t num_pages;