linux-kernel - [PATCH 07/29] drm/atomic: Implement drm_atomic_print_old

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Message-Id: <20250902-drm-state-readout-v1-7-14ad5315da3f@kernel.org>
Date: Tue, 02 Sep 2025 10:32:35 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
 Simona Vetter <simona@...ll.ch>, Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Jyri Sarha <jyri.sarha@....fi>, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Devarsh Thakkar <devarsht@...com>, dri-devel@...ts.freedesktop.org, 
 linux-kernel@...r.kernel.org, Maxime Ripard <mripard@...nel.org>
Subject: [PATCH 07/29] drm/atomic: Implement drm_atomic_print_old_state

We currently have a helper to print the new states associated to a
drm_atomic_state, but we don't have a variant to print the old state.

It's somewhat expected, since we almost never care about what the new
state looks like when we commit a new state, but we're about to change
that.

Signed-off-by: Maxime Ripard <mripard@...nel.org>
---
 drivers/gpu/drm/drm_atomic.c        | 45 +++++++++++++++++++++++++++++++++++++
 drivers/gpu/drm/drm_crtc_internal.h |  2 ++
 2 files changed, 47 insertions(+)

diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
index 9b198610791d19c7fd276ca59264a961d21caf43..38f2b2633fa992b3543e8c425c7faeab1ce69765 100644
--- a/drivers/gpu/drm/drm_atomic.c
+++ b/drivers/gpu/drm/drm_atomic.c
@@ -1875,10 +1875,55 @@ void drm_atomic_print_new_state(const struct drm_atomic_state *state,
 	for_each_new_private_obj_in_state(state, obj, obj_state, i)
 		drm_atomic_private_obj_print_state(p, obj_state);
 }
 EXPORT_SYMBOL(drm_atomic_print_new_state);
 
+/**
+ * drm_atomic_print_old_state - prints drm atomic state
+ * @state: atomic configuration to check
+ * @p: drm printer
+ *
+ * This functions prints the drm atomic state snapshot using the drm printer
+ * which is passed to it. This snapshot can be used for debugging purposes.
+ *
+ * Note that this function looks into the old state objects and hence its not
+ * safe to be used after the call to drm_atomic_helper_commit_hw_done().
+ */
+void drm_atomic_print_old_state(const struct drm_atomic_state *state,
+		struct drm_printer *p)
+{
+	struct drm_plane *plane;
+	struct drm_plane_state *plane_state;
+	struct drm_crtc *crtc;
+	struct drm_crtc_state *crtc_state;
+	struct drm_connector *connector;
+	struct drm_connector_state *connector_state;
+	struct drm_private_obj *obj;
+	struct drm_private_state *obj_state;
+	int i;
+
+	if (!p) {
+		drm_err(state->dev, "invalid drm printer\n");
+		return;
+	}
+
+	drm_dbg_atomic(state->dev, "checking %p\n", state);
+
+	for_each_old_plane_in_state(state, plane, plane_state, i)
+		drm_atomic_plane_print_state(p, plane_state);
+
+	for_each_old_crtc_in_state(state, crtc, crtc_state, i)
+		drm_atomic_crtc_print_state(p, crtc_state);
+
+	for_each_old_connector_in_state(state, connector, connector_state, i)
+		drm_atomic_connector_print_state(p, connector_state);
+
+	for_each_old_private_obj_in_state(state, obj, obj_state, i)
+		drm_atomic_private_obj_print_state(p, obj_state);
+}
+EXPORT_SYMBOL(drm_atomic_print_old_state);
+
 static void __drm_state_dump(struct drm_device *dev, struct drm_printer *p,
 			     bool take_locks)
 {
 	struct drm_mode_config *config = &dev->mode_config;
 	struct drm_plane *plane;
diff --git a/drivers/gpu/drm/drm_crtc_internal.h b/drivers/gpu/drm/drm_crtc_internal.h
index 89706aa8232fc0b2830af67c7588985a29653299..a8139fda1a1015c2ac8d8af3b12c5ac0b00cfc1a 100644
--- a/drivers/gpu/drm/drm_crtc_internal.h
+++ b/drivers/gpu/drm/drm_crtc_internal.h
@@ -249,10 +249,12 @@ int __drm_atomic_helper_disable_plane(struct drm_plane *plane,
 int __drm_atomic_helper_set_config(struct drm_mode_set *set,
 				   struct drm_atomic_state *state);
 
 void drm_atomic_print_new_state(const struct drm_atomic_state *state,
 		struct drm_printer *p);
+void drm_atomic_print_old_state(const struct drm_atomic_state *state,
+				struct drm_printer *p);
 
 /* drm_atomic_uapi.c */
 int drm_atomic_connector_commit_dpms(struct drm_atomic_state *state,
 				     struct drm_connector *connector,
 				     int mode);

-- 
2.50.1