From 178e5f3a5bc1d67d1248a74c0abab41040abe7c4 Mon Sep 17 00:00:00 2001
From: Brian Starkey <brian.starkey@arm.com>
Date: Tue, 6 Aug 2019 13:46:22 +0100
Subject: drm/crc-debugfs: Add notes about CRC<->commit interactions
Git-commit: 178e5f3a5bc1d67d1248a74c0abab41040abe7c4
Patch-mainline: v5.4-rc1
References: bsc#1152472
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 <brian.starkey@arm.com>
Signed-off-by: Ayan Kumar Halder <ayan.halder@arm.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link:- https://patchwork.freedesktop.org/patch/321974/
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
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:
*
--
2.28.0