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

From: Noralf TrÃnnes
Date: Tue Apr 26 2016 - 12:25:09 EST


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