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.
Changes since v1: - Clarified that anything that would disable CRCs counts as a full modeset, and so userspace needs to reconfigure after full modesets Changes since v2: - Add these notes - Rebase onto drm-misc-next (trivial conflict in comment) Signed-off-by: Brian Starkey <[email protected]> Reviewed-by: Daniel Vetter <[email protected]> --- drivers/gpu/drm/drm_debugfs_crc.c | 9 +++++++++ include/drm/drm_crtc.h | 4 ++++ 2 files changed, 13 insertions(+) diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c index 6604ed223160..be1b7ba92ffe 100644 --- a/drivers/gpu/drm/drm_debugfs_crc.c +++ b/drivers/gpu/drm/drm_debugfs_crc.c @@ -69,6 +69,15 @@ * implement &drm_crtc_funcs.set_crc_source and &drm_crtc_funcs.verify_crc_source. * The debugfs files are automatically set up if those vfuncs are 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: * -- 2.17.1
