Re: [PATCH v2 7/9] drm/simpledrm: Enable FB_DAMAGE_CLIPS property

["Noralf Trønnes" <noralf@tronnes.org>]

Den 09.11.2021 13.38, skrev Thomas Zimmermann:
> 
> 
> Am 08.11.21 um 21:55 schrieb Noralf Trønnes:
>>
>>
>> Den 01.11.2021 15.15, skrev Thomas Zimmermann:
>>> Enable the FB_DAMAGE_CLIPS property to reduce display-update
>>> overhead. Also fixes a warning in the kernel log.
>>>
>>>    simple-framebuffer simple-framebuffer.0: [drm]
>>> drm_plane_enable_fb_damage_clips() not called
>>>
>>> Fix the computation of the blit rectangle. This wasn't an issue so
>>> far, as simpledrm always blitted the full framebuffer. The code now
>>> supports damage clipping and virtual screen sizes.
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>>> ---
>>>   drivers/gpu/drm/tiny/simpledrm.c | 30 ++++++++++++++++++++++--------
>>>   1 file changed, 22 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/tiny/simpledrm.c
>>> b/drivers/gpu/drm/tiny/simpledrm.c
>>> index 571f716ff427..e872121e9fb0 100644
>>> --- a/drivers/gpu/drm/tiny/simpledrm.c
>>> +++ b/drivers/gpu/drm/tiny/simpledrm.c
>>> @@ -642,7 +642,7 @@ simpledrm_simple_display_pipe_enable(struct
>>> drm_simple_display_pipe *pipe,
>>>       void *vmap = shadow_plane_state->data[0].vaddr; /* TODO: Use
>>> mapping abstraction */
>>>       struct drm_device *dev = &sdev->dev;
>>>       void __iomem *dst = sdev->screen_base;
>>> -    struct drm_rect clip;
>>> +    struct drm_rect src_clip, dst_clip;
>>>       int idx;
>>>         if (!fb)
>>> @@ -651,10 +651,14 @@ simpledrm_simple_display_pipe_enable(struct
>>> drm_simple_display_pipe *pipe,
>>>       if (!drm_dev_enter(dev, &idx))
>>>           return;
>>>   -    drm_rect_init(&clip, 0, 0, fb->width, fb->height);
>>> +    drm_rect_fp_to_int(&src_clip, &plane_state->src);
>>>   -    dst += drm_fb_clip_offset(sdev->pitch, sdev->format, &clip);
>>> -    drm_fb_blit_toio(dst, sdev->pitch, sdev->format->format, vmap,
>>> fb, &clip);
>>> +    dst_clip = plane_state->dst;
>>
>> I assume that src_clip and dst_clip are of the same size, since scaling
>> is not supported. What prevents dst_clip from being bigger than the
>> buffer that's being blitted into? Where is that bounds checking done?
> 
> The value of dst_clip comes from plane_state->dst, which gets
> initialized in drm_atomic_helper_check_plane_state(). [1] The fields are
> taken from the crtc_{x,y,w,h} values by drm_plane_get_dest(). [2] For
> primary planes, the crtc_{x,y,w,h} values are initialized in
> __drm_atomic_helper_set_config() to the size of the display. [3] That
> size comes directly from the current video mode. [4] From all I can see
> this cannot overflow.
> 

Ok, that takes care of the upper bound.

There's this in drm_atomic_helper_check_plane_state():

	plane_state->visible = drm_rect_clip_scaled(src, dst, &clip);

	if (!plane_state->visible)
		/*
		 * Plane isn't visible; some drivers can handle this
		 * so we just return success here.  Drivers that can't
		 * (including those that use the primary plane helper's
		 * update function) will return an error from their
		 * update_plane handler.
		 */
		return 0;

drm_atomic_helper_damage_merged() checks ->visible and returns false if
it is not set so update() is good on the lower bound.

Maybe it's necessary to check ->visible here in enable() before doing
the blit?

Noralf.

> Best regards
> Thomas
> 
> [1]
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_atomic_helper.c#L807
> 
> [2]
> https://elixir.bootlin.com/linux/latest/source/include/drm/drm_plane.h#L257
> [3]
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_atomic.c#L1590
> 
> [4]
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_modes.c#L788
> 
> 
>>
>> Noralf.
>>
>>> +    if (!drm_rect_intersect(&dst_clip, &src_clip))
>>> +        return;
>>> +
>>> +    dst += drm_fb_clip_offset(sdev->pitch, sdev->format, &dst_clip);
>>> +    drm_fb_blit_toio(dst, sdev->pitch, sdev->format->format, vmap,
>>> fb, &src_clip);
>>>         drm_dev_exit(idx);
>>>   }
>>> @@ -686,20 +690,28 @@ simpledrm_simple_display_pipe_update(struct
>>> drm_simple_display_pipe *pipe,
>>>       struct drm_framebuffer *fb = plane_state->fb;
>>>       struct drm_device *dev = &sdev->dev;
>>>       void __iomem *dst = sdev->screen_base;
>>> -    struct drm_rect clip;
>>> +    struct drm_rect damage_clip, src_clip, dst_clip;
>>>       int idx;
>>>         if (!fb)
>>>           return;
>>>   -    if (!drm_atomic_helper_damage_merged(old_plane_state,
>>> plane_state, &clip))
>>> +    if (!drm_atomic_helper_damage_merged(old_plane_state,
>>> plane_state, &damage_clip))
>>> +        return;
>>> +
>>> +    drm_rect_fp_to_int(&src_clip, &plane_state->src);
>>> +    if (!drm_rect_intersect(&src_clip, &damage_clip))
>>> +        return;
>>> +
>>> +    dst_clip = plane_state->dst;
>>> +    if (!drm_rect_intersect(&dst_clip, &src_clip))
>>>           return;
>>>         if (!drm_dev_enter(dev, &idx))
>>>           return;
>>>   -    dst += drm_fb_clip_offset(sdev->pitch, sdev->format, &clip);
>>> -    drm_fb_blit_toio(dst, sdev->pitch, sdev->format->format, vmap,
>>> fb, &clip);
>>> +    dst += drm_fb_clip_offset(sdev->pitch, sdev->format, &dst_clip);
>>> +    drm_fb_blit_toio(dst, sdev->pitch, sdev->format->format, vmap,
>>> fb, &src_clip);
>>>         drm_dev_exit(idx);
>>>   }
>>> @@ -794,6 +806,8 @@ static int simpledrm_device_init_modeset(struct
>>> simpledrm_device *sdev)
>>>       if (ret)
>>>           return ret;
>>>   +    drm_plane_enable_fb_damage_clips(&pipe->plane);
>>> +
>>>       drm_mode_config_reset(dev);
>>>         return 0;
>>>
>