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drm/fb-helper: Acquire modeset lock around shadow-buffer flushing

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Flushing the fbdev's shadow buffer requires vmap'ing the BO memory, which
in turn requires pinning the BO. While being pinned, the BO cannot be moved
into VRAM for scanout. Consequently, a concurrent modeset operation that
involves the fbdev framebuffer would likely fail.

Resolve this problem be acquiring the modeset lock of the planes that use
the fbdev framebuffer. On non-atomic drivers, also acquire the mode-config
lock. This serializes the flushing of the framebuffer with concurrent
modeset operations.

v2:
	* only acquire struct drm_fb_helper.lock in damage blitter (Daniel,
	  Christian)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120102545.4047-11-tzimmermann@suse.de
This commit is contained in:
Thomas Zimmermann 2020-11-20 11:25:45 +01:00
parent 7d4d269c09
commit 32228ff5f7
1 changed files with 18 additions and 2 deletions
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20
drivers/gpu/drm/drm_fb_helper.c
View File

@ -398,16 +398,32 @@ static int drm_fb_helper_damage_blit(struct drm_fb_helper *fb_helper,
struct dma_buf_map map, dst;
int ret;
/*
* We have to pin the client buffer to its current location while
* flushing the shadow buffer. In the general case, concurrent
* modesetting operations could try to move the buffer and would
* fail. The modeset has to be serialized by acquiring the reservation
* object of the underlying BO here.
*
* For fbdev emulation, we only have to protect against fbdev modeset
* operations. Nothing else will involve the client buffer's BO. So it
* is sufficient to acquire struct drm_fb_helper.lock here.
*/
mutex_lock(&fb_helper->lock);
ret = drm_client_buffer_vmap(buffer, &map);
if (ret)
return ret;
goto out;
dst = map;
drm_fb_helper_damage_blit_real(fb_helper, clip, &dst);
drm_client_buffer_vunmap(buffer);
return 0;
out:
mutex_unlock(&fb_helper->lock);
return ret;
}
static void drm_fb_helper_damage_work(struct work_struct *work)