Re: [PATCH v3 2/8] drm/ast: Only map cursor BOs during updates

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Dec 09, 2020 at 03:25:21PM +0100, Thomas Zimmermann wrote:
> The HW cursor's BO used to be mapped permanently into the kernel's
> address space. GEM's vmap operation will be protected by locks, and
> we don't want to lock the BO's for an indefinate period of time.
> 
> Change the cursor code to map the HW BOs only during updates. The
> vmap operation in VRAM helpers is cheap, as a once estabished mapping
> is being reused until the BO actually moves. As the HW cursor BOs are
> permanently pinned, they never move at all.
> 
> v2:
> 	* fix typos in commit description
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> Acked-by: Christian König <christian.koenig@amd.com>

Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Now there's a pretty big issue here though: We can't take dma_resv_lock in
commit_tail, because of possible deadlocks on at least gpus that do real
async rendering because of the dma_fences. Unfortunately my annotations
patches got stuck a bit, I need to refresh them.

Rules are you can pin and unpin stuff in prepare/cleanup_plane, and also
take dma_resv_lock there, but not in commit_tail in-between. So I think
our vmap_local needs to loose the unconditional assert_locked and require
either that or a pin count.
-Daniel

> ---
>  drivers/gpu/drm/ast/ast_cursor.c | 51 ++++++++++++++++++--------------
>  drivers/gpu/drm/ast/ast_drv.h    |  2 --
>  2 files changed, 28 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_cursor.c b/drivers/gpu/drm/ast/ast_cursor.c
> index 68bf3d33f1ed..fac1ee79c372 100644
> --- a/drivers/gpu/drm/ast/ast_cursor.c
> +++ b/drivers/gpu/drm/ast/ast_cursor.c
> @@ -39,7 +39,6 @@ static void ast_cursor_fini(struct ast_private *ast)
>  
>  	for (i = 0; i < ARRAY_SIZE(ast->cursor.gbo); ++i) {
>  		gbo = ast->cursor.gbo[i];
> -		drm_gem_vram_vunmap(gbo, &ast->cursor.map[i]);
>  		drm_gem_vram_unpin(gbo);
>  		drm_gem_vram_put(gbo);
>  	}
> @@ -53,14 +52,13 @@ static void ast_cursor_release(struct drm_device *dev, void *ptr)
>  }
>  
>  /*
> - * Allocate cursor BOs and pins them at the end of VRAM.
> + * Allocate cursor BOs and pin them at the end of VRAM.
>   */
>  int ast_cursor_init(struct ast_private *ast)
>  {
>  	struct drm_device *dev = &ast->base;
>  	size_t size, i;
>  	struct drm_gem_vram_object *gbo;
> -	struct dma_buf_map map;
>  	int ret;
>  
>  	size = roundup(AST_HWC_SIZE + AST_HWC_SIGNATURE_SIZE, PAGE_SIZE);
> @@ -77,15 +75,7 @@ int ast_cursor_init(struct ast_private *ast)
>  			drm_gem_vram_put(gbo);
>  			goto err_drm_gem_vram_put;
>  		}
> -		ret = drm_gem_vram_vmap(gbo, &map);
> -		if (ret) {
> -			drm_gem_vram_unpin(gbo);
> -			drm_gem_vram_put(gbo);
> -			goto err_drm_gem_vram_put;
> -		}
> -
>  		ast->cursor.gbo[i] = gbo;
> -		ast->cursor.map[i] = map;
>  	}
>  
>  	return drmm_add_action_or_reset(dev, ast_cursor_release, NULL);
> @@ -94,7 +84,6 @@ int ast_cursor_init(struct ast_private *ast)
>  	while (i) {
>  		--i;
>  		gbo = ast->cursor.gbo[i];
> -		drm_gem_vram_vunmap(gbo, &ast->cursor.map[i]);
>  		drm_gem_vram_unpin(gbo);
>  		drm_gem_vram_put(gbo);
>  	}
> @@ -168,31 +157,38 @@ static void update_cursor_image(u8 __iomem *dst, const u8 *src, int width, int h
>  int ast_cursor_blit(struct ast_private *ast, struct drm_framebuffer *fb)
>  {
>  	struct drm_device *dev = &ast->base;
> -	struct drm_gem_vram_object *gbo;
> -	struct dma_buf_map map;
> -	int ret;
> -	void *src;
> +	struct drm_gem_vram_object *dst_gbo = ast->cursor.gbo[ast->cursor.next_index];
> +	struct drm_gem_vram_object *src_gbo = drm_gem_vram_of_gem(fb->obj[0]);
> +	struct dma_buf_map src_map, dst_map;
>  	void __iomem *dst;
> +	void *src;
> +	int ret;
>  
>  	if (drm_WARN_ON_ONCE(dev, fb->width > AST_MAX_HWC_WIDTH) ||
>  	    drm_WARN_ON_ONCE(dev, fb->height > AST_MAX_HWC_HEIGHT))
>  		return -EINVAL;
>  
> -	gbo = drm_gem_vram_of_gem(fb->obj[0]);
> -
> -	ret = drm_gem_vram_vmap(gbo, &map);
> +	ret = drm_gem_vram_vmap(src_gbo, &src_map);
>  	if (ret)
>  		return ret;
> -	src = map.vaddr; /* TODO: Use mapping abstraction properly */
> +	src = src_map.vaddr; /* TODO: Use mapping abstraction properly */
>  
> -	dst = ast->cursor.map[ast->cursor.next_index].vaddr_iomem;
> +	ret = drm_gem_vram_vmap(dst_gbo, &dst_map);
> +	if (ret)
> +		goto err_drm_gem_vram_vunmap;
> +	dst = dst_map.vaddr_iomem; /* TODO: Use mapping abstraction properly */
>  
>  	/* do data transfer to cursor BO */
>  	update_cursor_image(dst, src, fb->width, fb->height);
>  
> -	drm_gem_vram_vunmap(gbo, &map);
> +	drm_gem_vram_vunmap(dst_gbo, &dst_map);
> +	drm_gem_vram_vunmap(src_gbo, &src_map);
>  
>  	return 0;
> +
> +err_drm_gem_vram_vunmap:
> +	drm_gem_vram_vunmap(src_gbo, &src_map);
> +	return ret;
>  }
>  
>  static void ast_cursor_set_base(struct ast_private *ast, u64 address)
> @@ -243,17 +239,26 @@ static void ast_cursor_set_location(struct ast_private *ast, u16 x, u16 y,
>  void ast_cursor_show(struct ast_private *ast, int x, int y,
>  		     unsigned int offset_x, unsigned int offset_y)
>  {
> +	struct drm_device *dev = &ast->base;
> +	struct drm_gem_vram_object *gbo = ast->cursor.gbo[ast->cursor.next_index];
> +	struct dma_buf_map map;
>  	u8 x_offset, y_offset;
>  	u8 __iomem *dst;
>  	u8 __iomem *sig;
>  	u8 jreg;
> +	int ret;
>  
> -	dst = ast->cursor.map[ast->cursor.next_index].vaddr;
> +	ret = drm_gem_vram_vmap(gbo, &map);
> +	if (drm_WARN_ONCE(dev, ret, "drm_gem_vram_vmap() failed, ret=%d\n", ret))
> +		return;
> +	dst = map.vaddr_iomem; /* TODO: Use mapping abstraction properly */
>  
>  	sig = dst + AST_HWC_SIZE;
>  	writel(x, sig + AST_HWC_SIGNATURE_X);
>  	writel(y, sig + AST_HWC_SIGNATURE_Y);
>  
> +	drm_gem_vram_vunmap(gbo, &map);
> +
>  	if (x < 0) {
>  		x_offset = (-x) + offset_x;
>  		x = 0;
> diff --git a/drivers/gpu/drm/ast/ast_drv.h b/drivers/gpu/drm/ast/ast_drv.h
> index ccaff81924ee..f871fc36c2f7 100644
> --- a/drivers/gpu/drm/ast/ast_drv.h
> +++ b/drivers/gpu/drm/ast/ast_drv.h
> @@ -28,7 +28,6 @@
>  #ifndef __AST_DRV_H__
>  #define __AST_DRV_H__
>  
> -#include <linux/dma-buf-map.h>
>  #include <linux/i2c.h>
>  #include <linux/i2c-algo-bit.h>
>  #include <linux/io.h>
> @@ -133,7 +132,6 @@ struct ast_private {
>  
>  	struct {
>  		struct drm_gem_vram_object *gbo[AST_DEFAULT_HWC_NUM];
> -		struct dma_buf_map map[AST_DEFAULT_HWC_NUM];
>  		unsigned int next_index;
>  	} cursor;
>  
> -- 
> 2.29.2
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch