From 9f800214731fddb0a99810bcd1af8d93d22076e0 Mon Sep 17 00:00:00 2001
From: Daniel Vetter <daniel.vetter@ffwll.ch>
Date: Mon, 15 May 2017 11:11:36 +0200
Subject: [PATCH] drm/doc: Clarify mode_fixup vs. atomic_check a bit more
Git-commit: 9f800214731fddb0a99810bcd1af8d93d22076e0
Patch-mainline: v4.13-rc1
References: FATE#322643 bsc#1055900
Brought up by both Laurent and Andrzej when reviewing the new
->mode_valid hooks. Since mode_fixup is just a simpler version of the
much more generic atomic_check we can't really unify it with
mode_valid. Most drivers should probably switch their current
mode_fixup code to either the new mode_valid or the atomic_check
hooks, but e.g. that doesn't exist yet for bridges, and for CRTCs the
situation is a bit more complicated. Hence there's no clear
equivalence between mode_fixup and mode_valid, even if it looks like
that at first glance.
V2: Fix accidental double-dot (Adnrzej).
Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Jose Abreu <Jose.Abreu@synopsys.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170515091136.26307-2-daniel.vetter@ffwll.ch
Acked-by: Takashi Iwai <tiwai@suse.de>
---
include/drm/drm_modeset_helper_vtables.h | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
--- a/include/drm/drm_modeset_helper_vtables.h
+++ b/include/drm/drm_modeset_helper_vtables.h
@@ -165,7 +165,11 @@ struct drm_crtc_helper_funcs {
* allowed.
*
* Atomic drivers which need to inspect and adjust more state should
- * instead use the @atomic_check callback.
+ * instead use the @atomic_check callback, but note that they're not
+ * perfectly equivalent: @mode_valid is called from
+ * drm_atomic_helper_check_modeset(), but @atomic_check is called from
+ * drm_atomic_helper_check_planes(), because originally it was meant for
+ * plane update checks only.
*
* Also beware that userspace can request its own custom modes, neither
* core nor helpers filter modes to the list of probe modes reported by
@@ -547,7 +551,9 @@ struct drm_encoder_helper_funcs {
* allowed.
*
* Atomic drivers which need to inspect and adjust more state should
- * instead use the @atomic_check callback.
+ * instead use the @atomic_check callback. If @atomic_check is used,
+ * this hook isn't called since @atomic_check allows a strict superset
+ * of the functionality of @mode_fixup.
*
* Also beware that userspace can request its own custom modes, neither
* core nor helpers filter modes to the list of probe modes reported by
@@ -734,6 +740,11 @@ struct drm_encoder_helper_funcs {
* update the CRTC to match what the encoder needs for the requested
* connector.
*
+ * Since this provides a strict superset of the functionality of
+ * @mode_fixup (the requested and adjusted modes are both available
+ * through the passed in &struct drm_crtc_state) @mode_fixup is not
+ * called when @atomic_check is implemented.
+ *
* This function is used by the atomic helpers, but it is optional.
*
* NOTE: