Re: [PATCH 2/2] drm/omapdrm: Fix console with deferred ops

[Tony Lindgren <tony@atomide.com>]

* Thomas Zimmermann <tzimmermann@suse.de> [240220 09:32]:
> Am 20.02.24 um 09:56 schrieb Tony Lindgren:
> > Oh right, yes omapdrm is operating on memory.
> 
> With the latest kernels, you should see a warning if helpers operate on the
> wrong type of memory. [1][2]

OK

> [1] https://elixir.bootlin.com/linux/v6.8-rc5/source/drivers/video/fbdev/core/fb_io_fops.c#L16
> [2] https://elixir.bootlin.com/linux/v6.8-rc5/source/drivers/video/fbdev/core/fb_sys_fops.c#L26

> > The following test patch works for me.. Not sure about the tracking though.
> 
> I know that i915 doesn't track mmap'ed pages correctly and I've see systems
> that do not update the framebuffer. IDK how/why this works with omapdrm.

Sounds like the a similar issue might exist on omapdrm too then.

> > Do you mean that tracking needs to be implemented if fb_deferred_io_mmap()
> > did not work?
> 
> omap_fbdev_fb_mmap() appears to mmap the DMA memory pages directly to
> userspace. So the fb_dirty callback won't be invoked when userspace writes
> to this framebuffer memory.
> 
> To implement tracking, you'd need to set fb_mmap to fb_deferred_io_mmap().
> If you init omap_fb_ops with FB_DEFAULT_DEFERRED_OPS(), [3] you'd get that
> automatically. fb_deferred_io_mmap() sets up the tracking whenever
> userspaces writes to a mapped page.   You also need to init the write-back
> mechanisms that calls fb_dirty for the tracked pages. You should be able to
> duplicate the code from [4] into omapdrm.

OK great. Updated test patch below with FB_DEFAULT_DEFERRED_OPS, maybe that's
all there is to it if I follow you :) The fb_dirty part was already done in
patch 1/2.

> [3] https://elixir.bootlin.com/linux/latest/source/include/linux/fb.h#L704
> [4] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_fbdev_generic.c#L119

Regards,

Tony

8< ---------------------------
diff --git a/drivers/gpu/drm/omapdrm/omap_fbdev.c b/drivers/gpu/drm/omapdrm/omap_fbdev.c
--- a/drivers/gpu/drm/omapdrm/omap_fbdev.c
+++ b/drivers/gpu/drm/omapdrm/omap_fbdev.c
@@ -51,6 +51,10 @@ static void pan_worker(struct work_struct *work)
 	omap_gem_roll(bo, fbi->var.yoffset * npages);
 }
 
+FB_GEN_DEFAULT_DEFERRED_DMAMEM_OPS(omap_fbdev,
+				   drm_fb_helper_damage_range,
+				   drm_fb_helper_damage_area)
+
 static int omap_fbdev_pan_display(struct fb_var_screeninfo *var,
 		struct fb_info *fbi)
 {
@@ -76,15 +80,6 @@ static int omap_fbdev_pan_display(struct fb_var_screeninfo *var,
 	return drm_fb_helper_pan_display(var, fbi);
 }
 
-static int omap_fbdev_fb_mmap(struct fb_info *info, struct vm_area_struct *vma)
-{
-	struct drm_fb_helper *helper = info->par;
-	struct drm_framebuffer *fb = helper->fb;
-	struct drm_gem_object *bo = drm_gem_fb_get_obj(fb, 0);
-
-	return drm_gem_mmap_obj(bo, omap_gem_mmap_size(bo), vma);
-}
-
 static void omap_fbdev_fb_destroy(struct fb_info *info)
 {
 	struct drm_fb_helper *helper = info->par;
@@ -94,6 +89,7 @@ static void omap_fbdev_fb_destroy(struct fb_info *info)
 
 	DBG();
 
+	fb_deferred_io_cleanup(info);
 	drm_fb_helper_fini(helper);
 
 	omap_gem_unpin(bo);
@@ -106,15 +102,13 @@ static void omap_fbdev_fb_destroy(struct fb_info *info)
 
 static const struct fb_ops omap_fb_ops = {
 	.owner = THIS_MODULE,
-	__FB_DEFAULT_DMAMEM_OPS_RDWR,
+	FB_DEFAULT_DEFERRED_OPS(omap_fbdev),
 	.fb_check_var	= drm_fb_helper_check_var,
 	.fb_set_par	= drm_fb_helper_set_par,
 	.fb_setcmap	= drm_fb_helper_setcmap,
 	.fb_blank	= drm_fb_helper_blank,
 	.fb_pan_display = omap_fbdev_pan_display,
-	__FB_DEFAULT_DMAMEM_OPS_DRAW,
 	.fb_ioctl	= drm_fb_helper_ioctl,
-	.fb_mmap	= omap_fbdev_fb_mmap,
 	.fb_destroy	= omap_fbdev_fb_destroy,
 };
 
@@ -213,6 +207,15 @@ static int omap_fbdev_create(struct drm_fb_helper *helper,
 	fbi->fix.smem_start = dma_addr;
 	fbi->fix.smem_len = bo->size;
 
+	/* deferred I/O */
+	helper->fbdefio.delay = HZ / 20;
+	helper->fbdefio.deferred_io = drm_fb_helper_deferred_io;
+
+	fbi->fbdefio = &helper->fbdefio;
+	ret = fb_deferred_io_init(fbi);
+	if (ret)
+		goto fail;
+
 	/* if we have DMM, then we can use it for scrolling by just
 	 * shuffling pages around in DMM rather than doing sw blit.
 	 */
diff --git a/include/linux/fb.h b/include/linux/fb.h
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -686,6 +686,10 @@ extern int fb_deferred_io_fsync(struct file *file, loff_t start,
 	__FB_GEN_DEFAULT_DEFERRED_OPS_RDWR(__prefix, __damage_range, sys) \
 	__FB_GEN_DEFAULT_DEFERRED_OPS_DRAW(__prefix, __damage_area, sys)
 
+#define FB_GEN_DEFAULT_DEFERRED_DMAMEM_OPS(__prefix, __damage_range, __damage_area) \
+	__FB_GEN_DEFAULT_DEFERRED_OPS_RDWR(__prefix, __damage_range, sys) \
+	__FB_GEN_DEFAULT_DEFERRED_OPS_DRAW(__prefix, __damage_area, sys)
+
 /*
  * Initializes struct fb_ops for deferred I/O.
  */
-- 
2.43.1