drm/mgag200: Acquire I/O-register lock in atomic_commit_tail function

Hold I/O-register lock in atomic_commit_tail to protect all pipeline
updates at once. Protects against concurrent I/O access in get-modes
helper.

Complex modesetting operations involve mode changes, plane updates and
possibly BMC updates. Make all this atomic wrt to reading display modes
via EDID. It's not so much an issue with simple-KMS helpers, but will
become necessary for using regular atomic helpers.

v4:
	* remove empty line

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220728124103.30159-5-tzimmermann@suse.de

drivers/gpu/drm/mgag200/mgag200_mode.c

@@ -11,6 +11,7 @@
 #include <linux/delay.h>
 #include <linux/iosys-map.h>
 
+#include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_atomic_state_helper.h>
 #include <drm/drm_crtc_helper.h>
@@ -702,14 +703,6 @@ mgag200_simple_display_pipe_enable(struct drm_simple_display_pipe *pipe,
 		.y2 = fb->height,
 	};
 
-	/*
-	 * Concurrent operations could possibly trigger a call to
-	 * drm_connector_helper_funcs.get_modes by trying to read the
-	 * display modes. Protect access to I/O registers by acquiring
-	 * the I/O-register lock.
-	 */
-	mutex_lock(&mdev->rmmio_lock);
-
 	if (mdev->type == G200_WB || mdev->type == G200_EW3)
 		mgag200_g200wb_hold_bmc(mdev);
 
@@ -741,8 +734,6 @@ mgag200_simple_display_pipe_enable(struct drm_simple_display_pipe *pipe,
 	/* Always scanout image at VRAM offset 0 */
 	mgag200_set_startadd(mdev, (u32)0);
 	mgag200_set_offset(mdev, fb);
-
-	mutex_unlock(&mdev->rmmio_lock);
 }
 
 static void
@@ -812,8 +803,6 @@ mgag200_simple_display_pipe_update(struct drm_simple_display_pipe *pipe,
 	if (!fb)
 		return;
 
-	mutex_lock(&mdev->rmmio_lock);
-
 	if (crtc->state->color_mgmt_changed && crtc->state->gamma_lut)
 		mgag200_crtc_set_gamma(mdev, fb->format, crtc->state->gamma_lut->data);
 
@@ -824,8 +813,6 @@ mgag200_simple_display_pipe_update(struct drm_simple_display_pipe *pipe,
 	/* Always scanout image at VRAM offset 0 */
 	mgag200_set_startadd(mdev, (u32)0);
 	mgag200_set_offset(mdev, fb);
-
-	mutex_unlock(&mdev->rmmio_lock);
 }
 
 static struct drm_crtc_state *
@@ -903,6 +890,25 @@ static const uint64_t mgag200_simple_display_pipe_fmtmods[] = {
  * Mode config
  */
 
+static void mgag200_mode_config_helper_atomic_commit_tail(struct drm_atomic_state *state)
+{
+	struct mga_device *mdev = to_mga_device(state->dev);
+
+	/*
+	 * Concurrent operations could possibly trigger a call to
+	 * drm_connector_helper_funcs.get_modes by trying to read the
+	 * display modes. Protect access to I/O registers by acquiring
+	 * the I/O-register lock.
+	 */
+	mutex_lock(&mdev->rmmio_lock);
+	drm_atomic_helper_commit_tail(state);
+	mutex_unlock(&mdev->rmmio_lock);
+}
+
+static const struct drm_mode_config_helper_funcs mgag200_mode_config_helper_funcs = {
+	.atomic_commit_tail = mgag200_mode_config_helper_atomic_commit_tail,
+};
+
 /* Calculates a mode's required memory bandwidth (in KiB/sec). */
 static uint32_t mgag200_calculate_mode_bandwidth(const struct drm_display_mode *mode,
 						 unsigned int bits_per_pixel)
@@ -983,6 +989,7 @@ static int mgag200_mode_config_init(struct mga_device *mdev, resource_size_t vra
 	dev->mode_config.preferred_depth = 24;
 	dev->mode_config.fb_base = mdev->vram_res->start;
 	dev->mode_config.funcs = &mgag200_mode_config_funcs;
+	dev->mode_config.helper_private = &mgag200_mode_config_helper_funcs;
 
 	return 0;
 }