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

Am 11.12.20 um 11:18 schrieb Daniel Vetter:

On Wed, Dec 09, 2020 at 03:25:21PM +0100, Thomas Zimmermann wrote:

quoted

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 <redacted>

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.

I guess my commit description is misleading when it speaks of updates. 
ast_cursor_blit() is actually called from the cursor plane's prepare_fb 
function. [1] The vmap code in ast_cursor_show() could be moved into 
blit() as well, I think.

I guess the clean solution is to integrate the cursor code with the 
modesetting code in ast_mode. From there, locks and mappings can be 
established in prepare_fb and the HW state can be updated in atomic_commit.

Best regards
Thomas

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/ast/ast_mode.c#n646

-Daniel

quoted

---
  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

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer