drm/fbdev-dma: Implement damage handling and deferred I/O

Add support for damage handling and deferred I/O to fbdev-dma. This
enables fbdev-dma to support all DMA-memory-based DRM drivers, even
such with a dirty callback in their framebuffers.

The patch adds the code for deferred I/O and also sets a dedicated
helper for struct fb_ops.fb_mmap that support coherent mappings.

v3:
- init fb_ops with FB_GEN_DEFAULT_DEFERRED_DMAMEM_OPS() (Javier)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240419083331.7761-22-tzimmermann@suse.de

drivers/gpu/drm/drm_fbdev_dma.c

@@ -4,6 +4,7 @@
 
 #include <drm/drm_crtc_helper.h>
 #include <drm/drm_drv.h>
+#include <drm/drm_fb_dma_helper.h>
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_framebuffer.h>
 #include <drm/drm_gem_dma_helper.h>
@@ -35,6 +36,22 @@ static int drm_fbdev_dma_fb_release(struct fb_info *info, int user)
 	return 0;
 }
 
+FB_GEN_DEFAULT_DEFERRED_DMAMEM_OPS(drm_fbdev_dma,
+				   drm_fb_helper_damage_range,
+				   drm_fb_helper_damage_area);
+
+static int drm_fbdev_dma_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
+{
+	struct drm_fb_helper *fb_helper = info->par;
+	struct drm_framebuffer *fb = fb_helper->fb;
+	struct drm_gem_dma_object *dma = drm_fb_dma_get_gem_obj(fb, 0);
+
+	if (!dma->map_noncoherent)
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+
+	return fb_deferred_io_mmap(info, vma);
+}
+
 static void drm_fbdev_dma_fb_destroy(struct fb_info *info)
 {
 	struct drm_fb_helper *fb_helper = info->par;
@@ -51,20 +68,13 @@ static void drm_fbdev_dma_fb_destroy(struct fb_info *info)
 	kfree(fb_helper);
 }
 
-static int drm_fbdev_dma_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
-{
-	struct drm_fb_helper *fb_helper = info->par;
-
-	return drm_gem_prime_mmap(fb_helper->buffer->gem, vma);
-}
-
 static const struct fb_ops drm_fbdev_dma_fb_ops = {
 	.owner = THIS_MODULE,
 	.fb_open = drm_fbdev_dma_fb_open,
 	.fb_release = drm_fbdev_dma_fb_release,
-	__FB_DEFAULT_DMAMEM_OPS_RDWR,
+	__FB_DEFAULT_DEFERRED_OPS_RDWR(drm_fbdev_dma),
 	DRM_FB_HELPER_DEFAULT_OPS,
-	__FB_DEFAULT_DMAMEM_OPS_DRAW,
+	__FB_DEFAULT_DEFERRED_OPS_DRAW(drm_fbdev_dma),
 	.fb_mmap = drm_fbdev_dma_fb_mmap,
 	.fb_destroy = drm_fbdev_dma_fb_destroy,
 };
@@ -98,10 +108,6 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 	dma_obj = to_drm_gem_dma_obj(buffer->gem);
 
 	fb = buffer->fb;
-	if (drm_WARN_ON(dev, fb->funcs->dirty)) {
-		ret = -ENODEV; /* damage handling not supported; use generic emulation */
-		goto err_drm_client_buffer_delete;
-	}
 
 	ret = drm_client_buffer_vmap(buffer, &map);
 	if (ret) {
@@ -112,7 +118,7 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 	}
 
 	fb_helper->buffer = buffer;
-	fb_helper->fb = buffer->fb;
+	fb_helper->fb = fb;
 
 	info = drm_fb_helper_alloc_info(fb_helper);
 	if (IS_ERR(info)) {
@@ -133,8 +139,19 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 	info->fix.smem_start = page_to_phys(virt_to_page(info->screen_buffer));
 	info->fix.smem_len = info->screen_size;
 
+	/* deferred I/O */
+	fb_helper->fbdefio.delay = HZ / 20;
+	fb_helper->fbdefio.deferred_io = drm_fb_helper_deferred_io;
+
+	info->fbdefio = &fb_helper->fbdefio;
+	ret = fb_deferred_io_init(info);
+	if (ret)
+		goto err_drm_fb_helper_release_info;
+
 	return 0;
 
+err_drm_fb_helper_release_info:
+	drm_fb_helper_release_info(fb_helper);
 err_drm_client_buffer_vunmap:
 	fb_helper->fb = NULL;
 	fb_helper->buffer = NULL;
@@ -144,8 +161,28 @@ static int drm_fbdev_dma_helper_fb_probe(struct drm_fb_helper *fb_helper,
 	return ret;
 }
 
+static int drm_fbdev_dma_helper_fb_dirty(struct drm_fb_helper *helper,
+					 struct drm_clip_rect *clip)
+{
+	struct drm_device *dev = helper->dev;
+	int ret;
+
+	/* Call damage handlers only if necessary */
+	if (!(clip->x1 < clip->x2 && clip->y1 < clip->y2))
+		return 0;
+
+	if (helper->fb->funcs->dirty) {
+		ret = helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, clip, 1);
+		if (drm_WARN_ONCE(dev, ret, "Dirty helper failed: ret=%d\n", ret))
+			return ret;
+	}
+
+	return 0;
+}
+
 static const struct drm_fb_helper_funcs drm_fbdev_dma_helper_funcs = {
 	.fb_probe = drm_fbdev_dma_helper_fb_probe,
+	.fb_dirty = drm_fbdev_dma_helper_fb_dirty,
 };
 
 /*