Commit d8c4bddc authored by Thomas Zimmermann's avatar Thomas Zimmermann
Browse files

drm/fb-helper: Synchronize dirty worker with vblank 



Before updating the display from the console's shadow buffer, the dirty
worker now waits for a vblank. This allows several screen updates to pile
up and acts as a rate limiter. If a DRM master is present, it could
interfere with the vblank. Don't wait in this case.

v4:
	* share code with WAITFORVSYNC ioctl (Emil)
	* use lock guard
v3:
	* add back helper->lock
	* acquire DRM master status while waiting for vblank
v2:
	* don't hold helper->lock while waiting for vblank

Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Acked-by: default avatarSam Ravnborg <sam@ravnborg.org>
Link: https://lore.kernel.org/r/20250829091447.46719-1-tzimmermann@suse.de
parent cf207ea2

drivers/gpu/drm/drm_client_modeset.c

+44 −0
Original line number Diff line number Diff line
@@ -1293,6 +1293,50 @@ int drm_client_modeset_dpms(struct drm_client_dev *client, int mode) 
}

EXPORT_SYMBOL(drm_client_modeset_dpms);



/**

 * drm_client_modeset_wait_for_vblank() - Wait for the next VBLANK to occur

 * @client: DRM client

 * @crtc_index: The ndex of the CRTC to wait on

 *

 * Block the caller until the given CRTC has seen a VBLANK. Do nothing

 * if the CRTC is disabled. If there's another DRM master present, fail

 * with -EBUSY.

 *

 * Returns:

 * 0 on success, or negative error code otherwise.

 */

int drm_client_modeset_wait_for_vblank(struct drm_client_dev *client, unsigned int crtc_index)

{

	struct drm_device *dev = client->dev;

	struct drm_crtc *crtc;

	int ret;



	/*

	 * Rate-limit update frequency to vblank. If there's a DRM master

	 * present, it could interfere while we're waiting for the vblank

	 * event. Don't wait in this case.

	 */

	if (!drm_master_internal_acquire(dev))

		return -EBUSY;



	crtc = client->modesets[crtc_index].crtc;



	/*

	 * Only wait for a vblank event if the CRTC is enabled, otherwise

	 * just don't do anything, not even report an error.

	 */

	ret = drm_crtc_vblank_get(crtc);

	if (!ret) {

		drm_crtc_wait_one_vblank(crtc);

		drm_crtc_vblank_put(crtc);

	}



	drm_master_internal_release(dev);



	return 0;

}

EXPORT_SYMBOL(drm_client_modeset_wait_for_vblank);



#ifdef CONFIG_DRM_KUNIT_TEST

#include "tests/drm_client_modeset_test.c"

#endif

drivers/gpu/drm/drm_fb_helper.c

+6 −24
Original line number Diff line number Diff line
@@ -368,6 +368,10 @@ static void drm_fb_helper_fb_dirty(struct drm_fb_helper *helper) 
	unsigned long flags;

	int ret;



	mutex_lock(&helper->lock);

	drm_client_modeset_wait_for_vblank(&helper->client, 0);

	mutex_unlock(&helper->lock);



	if (drm_WARN_ON_ONCE(dev, !helper->funcs->fb_dirty))

		return;
@@ -1068,15 +1072,9 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, 
			unsigned long arg)

{

	struct drm_fb_helper *fb_helper = info->par;

	struct drm_device *dev = fb_helper->dev;

	struct drm_crtc *crtc;

	int ret = 0;



	mutex_lock(&fb_helper->lock);

	if (!drm_master_internal_acquire(dev)) {

		ret = -EBUSY;

		goto unlock;

	}

	guard(mutex)(&fb_helper->lock);



	switch (cmd) {

	case FBIO_WAITFORVSYNC:
@@ -1096,28 +1094,12 @@ int drm_fb_helper_ioctl(struct fb_info *info, unsigned int cmd, 
		 * make. If we're not smart enough here, one should

		 * just consider switch the userspace to KMS.

		 */

		crtc = fb_helper->client.modesets[0].crtc;



		/*

		 * Only wait for a vblank event if the CRTC is

		 * enabled, otherwise just don't do anythintg,

		 * not even report an error.

		 */

		ret = drm_crtc_vblank_get(crtc);

		if (!ret) {

			drm_crtc_wait_one_vblank(crtc);

			drm_crtc_vblank_put(crtc);

		}



		ret = 0;

		ret = drm_client_modeset_wait_for_vblank(&fb_helper->client, 0);

		break;

	default:

		ret = -ENOTTY;

	}



	drm_master_internal_release(dev);

unlock:

	mutex_unlock(&fb_helper->lock);

	return ret;

}

EXPORT_SYMBOL(drm_fb_helper_ioctl);

include/drm/drm_client.h

+1 −0
Original line number Diff line number Diff line
@@ -220,6 +220,7 @@ int drm_client_modeset_check(struct drm_client_dev *client); 
int drm_client_modeset_commit_locked(struct drm_client_dev *client);

int drm_client_modeset_commit(struct drm_client_dev *client);

int drm_client_modeset_dpms(struct drm_client_dev *client, int mode);

int drm_client_modeset_wait_for_vblank(struct drm_client_dev *client, unsigned int crtc_index);



/**

 * drm_client_for_each_modeset() - Iterate over client modesets