Re: [PATCH v2 4/8] drm/fb-helper: Add fb_deferred_io support

Noralf Trønnes <noralf@xxxxxxxxxxx> · Tue, 26 Apr 2016 18:24:54 +0200

Den 25.04.2016 11:09, skrev Daniel Vetter:
On Sun, Apr 24, 2016 at 10:48:58PM +0200, Noralf Trønnes wrote:
This adds deferred io support if CONFIG_FB_DEFERRED_IO is enabled.
The fbdev framebuffer changes are flushed using the callback
(struct drm_framebuffer *)->funcs->dirty() by a dedicated worker
ensuring that it always runs in process context.

Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
---

Changes since v1:
- Use a dedicated worker to run the framebuffer flushing like qxl does
- Add parameter descriptions to drm_fb_helper_deferred_io

  drivers/gpu/drm/drm_fb_helper.c | 127 +++++++++++++++++++++++++++++++++++++++-
  include/drm/drm_fb_helper.h     |  17 ++++++
  2 files changed, 143 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 855108e..46ee6f8 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -40,6 +40,7 @@
  #include <drm/drm_crtc_helper.h>
  #include <drm/drm_atomic.h>
  #include <drm/drm_atomic_helper.h>
+#include <drm/drm_rect.h>

  static bool drm_fbdev_emulation = true;
  module_param_named(fbdev_emulation, drm_fbdev_emulation, bool, 0600);
@@ -48,6 +49,10 @@ MODULE_PARM_DESC(fbdev_emulation,

  static LIST_HEAD(kernel_fb_helper_list);

+static void drm_fb_helper_dirty_init(struct drm_fb_helper *helper);
+static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y,
+				u32 width, u32 height);
+
  /**
   * DOC: fbdev helpers
   *
@@ -84,6 +89,16 @@ static LIST_HEAD(kernel_fb_helper_list);
   * and set up an initial configuration using the detected hardware, drivers
   * should call drm_fb_helper_single_add_all_connectors() followed by
   * drm_fb_helper_initial_config().
+ *
+ * If CONFIG_FB_DEFERRED_IO is enabled and
+ * (struct drm_framebuffer *)->funcs->dirty is set, the
+ * drm_fb_helper_{cfb,sys}_{write,fillrect,copyarea,imageblit} functions
+ * will accumulate changes and schedule (struct fb_helper).dirty_work to run
+ * right away. This worker then calls the dirty() function ensuring that it
+ * will always run in process context since the fb_*() function could be
+ * running in atomic context. If drm_fb_helper_deferred_io() is used as the
+ * deferred_io callback it will also schedule dirty_work with the damage
+ * collected from the mmap page writes.
One thing to consider (and personally I don't care either way) is whether
we shouldn't just select CONFIG_FB_DEFERRED_IO if the fbdev helpers are
enabled. Pushing that out to drivers is imo a bit fragile.

But like I said I'm ok with either way.

My concern was adding code and data that only a few drivers would
actually use. But of course there's the tradeoff with complexity.
I use this to enable it:
        select FB_DEFERRED_IO if DRM_KMS_FB_HELPER

I guess the maintainer has to make this choice between size and 
complexity :-)
I can enable it by default if you want, drm is both huge and complex so I
don't know what's best.

As a sidenote, I have also put all the fbdev code in a file of it's own to
make it simple with regards to the DRM_FBDEV_EMULATION user option:
tinydrm-$(CONFIG_DRM_KMS_FB_HELPER)     += tinydrm-fbdev.o

   */

  /**
@@ -401,11 +416,14 @@ backoff:
  static int restore_fbdev_mode(struct drm_fb_helper *fb_helper)
  {
  	struct drm_device *dev = fb_helper->dev;
+	struct fb_info *info = fb_helper->fbdev;
  	struct drm_plane *plane;
  	int i;

  	drm_warn_on_modeset_not_all_locked(dev);

+	drm_fb_helper_dirty(info, 0, 0, info->var.xres, info->var.yres);
Why is this needed? If you do a modeset (or pageflip or whatever) drivers
are supposed to re-upload the entire screen. We've talked about adding a
dirty rectangle to atomic to allow userspace to optimize this, but there
should _never_ be a need to do a dirtyfb call around a modeset. Probably
just a driver bug in your panel drm drivers?

Ok, in tinydrm I now set a flag in &drm_simple_display_pipe_funcs
->plane_update to indicate that the next dirty() should do the whole
framebuffer which seems to work fine.
Should I actually perform the update as well?
If so I would need to add a worker in tinydrm to do that.


Noralf.

With the above line removed:

Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

+
  	if (fb_helper->atomic)
  		return restore_fbdev_mode_atomic(fb_helper);

@@ -650,6 +668,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
  			   const struct drm_fb_helper_funcs *funcs)
  {
  	INIT_LIST_HEAD(&helper->kernel_fb_list);
+	drm_fb_helper_dirty_init(helper);
  	helper->funcs = funcs;
  	helper->dev = dev;
  }
@@ -834,6 +853,93 @@ void drm_fb_helper_unlink_fbi(struct drm_fb_helper *fb_helper)
  }
  EXPORT_SYMBOL(drm_fb_helper_unlink_fbi);

+#ifdef CONFIG_FB_DEFERRED_IO
+static void drm_fb_helper_dirty_work(struct work_struct *work)
+{
+	struct drm_fb_helper *helper = container_of(work, struct drm_fb_helper,
+						    dirty_work);
+	struct drm_clip_rect clip;
+	unsigned long flags;
+
+	spin_lock_irqsave(&helper->dirty_lock, flags);
+	clip = helper->dirty_clip;
+	drm_clip_rect_reset(&helper->dirty_clip);
+	spin_unlock_irqrestore(&helper->dirty_lock, flags);
+
+	helper->fb->funcs->dirty(helper->fb, NULL, 0, 0, &clip, 1);
+}
+
+static void drm_fb_helper_dirty_init(struct drm_fb_helper *helper)
+{
+	spin_lock_init(&helper->dirty_lock);
+	INIT_WORK(&helper->dirty_work, drm_fb_helper_dirty_work);
+}
+
+static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y,
+				u32 width, u32 height)
+{
+	struct drm_fb_helper *helper = info->par;
+	struct drm_clip_rect clip;
+	unsigned long flags;
+
+	if (!helper->fb->funcs->dirty)
+		return;
+
+	clip.x1 = x;
+	clip.x2 = x + width;
+	clip.y1 = y;
+	clip.y2 = y + height;
+
+	spin_lock_irqsave(&helper->dirty_lock, flags);
+	drm_clip_rect_merge(&helper->dirty_clip, &clip, 1, 0, 0, 0);
+	spin_unlock_irqrestore(&helper->dirty_lock, flags);
+
+	schedule_work(&helper->dirty_work);
+}
+
+/**
+ * drm_fb_helper_deferred_io() - fbdev deferred_io callback function
+ * @info: fb_info struct pointer
+ * @pagelist: list of dirty mmap framebuffer pages
+ *
+ * This function is used as the (struct fb_deferred_io *)->deferred_io
+ * callback function for flushing the fbdev mmap writes.
+ */
+void drm_fb_helper_deferred_io(struct fb_info *info,
+			       struct list_head *pagelist)
+{
+	unsigned long start, end, min, max;
+	struct page *page;
+	u32 y1, y2;
+
+	min = ULONG_MAX;
+	max = 0;
+	list_for_each_entry(page, pagelist, lru) {
+		start = page->index << PAGE_SHIFT;
+		end = start + PAGE_SIZE - 1;
+		min = min(min, start);
+		max = max(max, end);
+	}
+
+	if (min < max) {
+		y1 = min / info->fix.line_length;
+		y2 = min_t(u32, max / info->fix.line_length, info->var.yres);
+		drm_fb_helper_dirty(info, 0, y1, info->var.xres, y2 - y1);
+	}
+}
+EXPORT_SYMBOL(drm_fb_helper_deferred_io);
+
+#else
+static void drm_fb_helper_dirty_init(struct drm_fb_helper *helper)
+{
+}
+
+static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y,
+				u32 width, u32 height)
+{
+}
+#endif /* CONFIG_FB_DEFERRED_IO */
+
  /**
   * drm_fb_helper_sys_read - wrapper around fb_sys_read
   * @info: fb_info struct pointer
@@ -862,7 +968,14 @@ EXPORT_SYMBOL(drm_fb_helper_sys_read);
  ssize_t drm_fb_helper_sys_write(struct fb_info *info, const char __user *buf,
  				size_t count, loff_t *ppos)
  {
-	return fb_sys_write(info, buf, count, ppos);
+	ssize_t ret;
+
+	ret = fb_sys_write(info, buf, count, ppos);
+	if (ret > 0)
+		drm_fb_helper_dirty(info, 0, 0, info->var.xres,
+				    info->var.yres);
+
+	return ret;
  }
  EXPORT_SYMBOL(drm_fb_helper_sys_write);

@@ -877,6 +990,8 @@ void drm_fb_helper_sys_fillrect(struct fb_info *info,
  				const struct fb_fillrect *rect)
  {
  	sys_fillrect(info, rect);
+	drm_fb_helper_dirty(info, rect->dx, rect->dy,
+			    rect->width, rect->height);
  }
  EXPORT_SYMBOL(drm_fb_helper_sys_fillrect);

@@ -891,6 +1006,8 @@ void drm_fb_helper_sys_copyarea(struct fb_info *info,
  				const struct fb_copyarea *area)
  {
  	sys_copyarea(info, area);
+	drm_fb_helper_dirty(info, area->dx, area->dy,
+			    area->width, area->height);
  }
  EXPORT_SYMBOL(drm_fb_helper_sys_copyarea);

@@ -905,6 +1022,8 @@ void drm_fb_helper_sys_imageblit(struct fb_info *info,
  				 const struct fb_image *image)
  {
  	sys_imageblit(info, image);
+	drm_fb_helper_dirty(info, image->dx, image->dy,
+			    image->width, image->height);
  }
  EXPORT_SYMBOL(drm_fb_helper_sys_imageblit);

@@ -919,6 +1038,8 @@ void drm_fb_helper_cfb_fillrect(struct fb_info *info,
  				const struct fb_fillrect *rect)
  {
  	cfb_fillrect(info, rect);
+	drm_fb_helper_dirty(info, rect->dx, rect->dy,
+			    rect->width, rect->height);
  }
  EXPORT_SYMBOL(drm_fb_helper_cfb_fillrect);

@@ -933,6 +1054,8 @@ void drm_fb_helper_cfb_copyarea(struct fb_info *info,
  				const struct fb_copyarea *area)
  {
  	cfb_copyarea(info, area);
+	drm_fb_helper_dirty(info, area->dx, area->dy,
+			    area->width, area->height);
  }
  EXPORT_SYMBOL(drm_fb_helper_cfb_copyarea);

@@ -947,6 +1070,8 @@ void drm_fb_helper_cfb_imageblit(struct fb_info *info,
  				 const struct fb_image *image)
  {
  	cfb_imageblit(info, image);
+	drm_fb_helper_dirty(info, image->dx, image->dy,
+			    image->width, image->height);
  }
  EXPORT_SYMBOL(drm_fb_helper_cfb_imageblit);

diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
index 062723b..dde825c 100644
--- a/include/drm/drm_fb_helper.h
+++ b/include/drm/drm_fb_helper.h
@@ -172,6 +172,10 @@ struct drm_fb_helper_connector {
   * @funcs: driver callbacks for fb helper
   * @fbdev: emulated fbdev device info struct
   * @pseudo_palette: fake palette of 16 colors
+ * @dirty_clip: clip rectangle used with deferred_io to accumulate damage to
+ *              the screen buffer
+ * @dirty_lock: spinlock protecting @dirty_clip
+ * @dirty_work: worker used to flush the framebuffer
   *
   * This is the main structure used by the fbdev helpers. Drivers supporting
   * fbdev emulation should embedded this into their overall driver structure.
@@ -189,6 +193,11 @@ struct drm_fb_helper {
  	const struct drm_fb_helper_funcs *funcs;
  	struct fb_info *fbdev;
  	u32 pseudo_palette[17];
+#ifdef CONFIG_FB_DEFERRED_IO
+	struct drm_clip_rect dirty_clip;
+	spinlock_t dirty_lock;
+	struct work_struct dirty_work;
+#endif

  	/**
  	 * @kernel_fb_list:
@@ -245,6 +254,9 @@ void drm_fb_helper_fill_fix(struct fb_info *info, uint32_t pitch,

  void drm_fb_helper_unlink_fbi(struct drm_fb_helper *fb_helper);

+void drm_fb_helper_deferred_io(struct fb_info *info,
+			       struct list_head *pagelist);
+
  ssize_t drm_fb_helper_sys_read(struct fb_info *info, char __user *buf,
  			       size_t count, loff_t *ppos);
  ssize_t drm_fb_helper_sys_write(struct fb_info *info, const char __user *buf,
@@ -368,6 +380,11 @@ static inline void drm_fb_helper_unlink_fbi(struct drm_fb_helper *fb_helper)
  {
  }

+static inline void drm_fb_helper_deferred_io(struct fb_info *info,
+					     struct list_head *pagelist)
+{
+}
+
  static inline ssize_t drm_fb_helper_sys_read(struct fb_info *info,
  					     char __user *buf, size_t count,
  					     loff_t *ppos)
--
2.2.2


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