Re: [PATCH v4 3/7] drm/fb-helper: Add fb_deferred_io support

Tomi Valkeinen
2016-04-29T12:51:09Z

[-- Attachment #1.1: Type: text/plain, Size: 2999 bytes --]

Hi,

On 28/04/16 18:18, Noralf Trønnes wrote:
> This adds deferred io support to drm_fb_helper.
> 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@tronnes.org>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---

Thanks for the series! Unfortunately I haven't been able to follow the
discussions properly, so I hope my questions haven't been covered earlier.

> Changes since v3:
> - Don't use forward decl, move drm_fb_helper_dirty_work()
> - Use DIV_ROUND_UP in drm_fb_helper_deferred_io()
>
> Changes since v2:
> - FB_DEFERRED_IO is now always selected by DRM_KMS_FB_HELPER, ifdef removed
> - The drm_clip_rect utility functions are dropped, so open code it
> - docs: use & to denote structs
>
> 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/Kconfig | 1 +
> drivers/gpu/drm/drm_fb_helper.c | 103 +++++++++++++++++++++++++++++++++++++++-
> include/drm/drm_fb_helper.h | 15 ++++++
> 3 files changed, 118 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 9e4f2f1..8e6f34b 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -52,6 +52,7 @@ config DRM_KMS_FB_HELPER
> select FB_CFB_FILLRECT
> select FB_CFB_COPYAREA
> select FB_CFB_IMAGEBLIT
> + select FB_DEFERRED_IO
> help
> FBDEV helpers for KMS drivers.
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 855108e..62f849f 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -84,6 +84,15 @@ 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 &drm_framebuffer_funcs ->dirty is
> + * set, the drm_fb_helper_{cfb,sys}_{write,fillrect,copyarea,imageblit}
> + * functions will accumulate changes and schedule &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

Who's calling {write,fillrect,copyarea,imageblit} in an atomic context?
That sounds like a very bad idea to me...

If this is only for accumulating changes, I think it may be better to
leave that to the driver as it may have better idea of how to accumulate.

But, of course, this is a helper, so if all the drivers use this kind of
accumulation, it makes sense =).

Tomi

[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]