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

[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.

>   */
> 
>  /**
> @@ -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?

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
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch