CRC generation can be impacted by commits coming from userspace, and enabling CRC generation may itself trigger a commit. Add notes about this to the kerneldoc.
Signed-off-by: Brian Starkey brian.starkey@arm.com --- drivers/gpu/drm/drm_debugfs_crc.c | 17 +++++++++++++---- include/drm/drm_crtc.h | 4 ++++ 2 files changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c index 7ca486d750e9..77159b6e77c3 100644 --- a/drivers/gpu/drm/drm_debugfs_crc.c +++ b/drivers/gpu/drm/drm_debugfs_crc.c @@ -65,10 +65,19 @@ * it submits. In this general case, the maximum userspace can do is to compare * the reported CRCs of frames that should have the same contents. * - * On the driver side the implementation effort is minimal, drivers only need to - * implement &drm_crtc_funcs.set_crc_source. The debugfs files are automatically - * set up if that vfunc is set. CRC samples need to be captured in the driver by - * calling drm_crtc_add_crc_entry(). + * On the driver side the implementation effort is minimal, drivers only need + * to implement &drm_crtc_funcs.set_crc_source. The debugfs files are + * automatically set up if that vfunc is set. CRC samples need to be captured + * in the driver by calling drm_crtc_add_crc_entry(). Depending on the driver + * and HW requirements, &drm_crtc_funcs.set_crc_source may result in a commit + * (even a full modeset). + * + * CRC results must be reliable across non-full-modeset atomic commits, so if a + * commit via DRM_IOCTL_MODE_ATOMIC would disable or otherwise interfere with + * CRC generation, then the driver must mark that commit as a full modeset + * (drm_atomic_crtc_needs_modeset() should return true). As a result, to ensure + * consistent results, generic userspace must re-setup CRC generation after a + * legacy SETCRTC or an atomic commit with DRM_MODE_ATOMIC_ALLOW_MODESET. */
static int crc_control_show(struct seq_file *m, void *data) diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h index 128d8b210621..7d14c11bdc0a 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -756,6 +756,9 @@ struct drm_crtc_funcs { * provided from the configured source. Drivers must accept an "auto" * source name that will select a default source for this CRTC. * + * This may trigger an atomic modeset commit if necessary, to enable CRC + * generation. + * * Note that "auto" can depend upon the current modeset configuration, * e.g. it could pick an encoder or output specific CRC sampling point. * @@ -767,6 +770,7 @@ struct drm_crtc_funcs { * 0 on success or a negative error code on failure. */ int (*set_crc_source)(struct drm_crtc *crtc, const char *source); + /** * @verify_crc_source: *