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 ---
I might have got the wrong end of the stick, but this is what I understood from what you said.
Cheers, -Brian
drivers/gpu/drm/drm_debugfs_crc.c | 15 +++++++++++---- include/drm/drm_crtc.h | 3 +++ 2 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c index 7ca486d750e9..1dff956bcc74 100644 --- a/drivers/gpu/drm/drm_debugfs_crc.c +++ b/drivers/gpu/drm/drm_debugfs_crc.c @@ -65,10 +65,17 @@ * 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). + * + * It's also possible that a "normal" commit via DRM_IOCTL_MODE_ATOMIC or the + * legacy paths may interfere with CRC generation. So, in the general case, + * userspace can't rely on the values in crtc-N/crc/data being valid + * across a commit. */
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..0f7ea094a900 100644 --- a/include/drm/drm_crtc.h +++ b/include/drm/drm_crtc.h @@ -756,6 +756,8 @@ 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 a 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 +769,7 @@ 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: *