drm/i915: Factor out a helper for handling atomic modeset locks/state

This patch simplifying the handling of modeset locks and atomic state
for an atomic commit is based on

https://lore.kernel.org/all/20210715184954.7794-2-ville.syrjala@linux.intel.com/

adding the helper to i915. I find this approach preferrable than
open-coding the corresponding steps (fixed for me an atomic
state reset during a DEADLK retry, which I missed in the open-coded
version) and also better than the existing
DRM_MODESET_LOCK_ALL_BEGIN/END macros for the reasons described in the
above original patchset.

This change takes the helper into use only for atomic commits during DDI
hotplug handling, as a preparation for a follow-up patch adding a
similar commit started from the same spot. Other places doing a
driver-internal atomic commit is to be converted by a follow-up
patchset.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230510103131.1618266-13-imre.deak@intel.com

1 files changed, 50 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_modeset_lock.c b/drivers/gpu/drm/i915/display/intel_modeset_lock.c
new file mode 100644
index 000000000000..8fb6fd849a75
--- /dev/null
+++ b/drivers/gpu/drm/i915/display/intel_modeset_lock.c
@@ -0,0 +1,50 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2023 Intel Corporation
+ */
+
+#include <drm/drm_modeset_lock.h>
+
+#include "intel_display_types.h"
+#include "intel_modeset_lock.h"
+
+void _intel_modeset_lock_begin(struct drm_modeset_acquire_ctx *ctx,
+			       struct intel_atomic_state *state,
+			       unsigned int flags, int *ret)
+{
+	drm_modeset_acquire_init(ctx, flags);
+
+	if (state)
+		state->base.acquire_ctx = ctx;
+
+	*ret = -EDEADLK;
+}
+
+bool _intel_modeset_lock_loop(int *ret)
+{
+	if (*ret == -EDEADLK) {
+		*ret = 0;
+		return true;
+	}
+
+	return false;
+}
+
+void _intel_modeset_lock_end(struct drm_modeset_acquire_ctx *ctx,
+			     struct intel_atomic_state *state,
+			     int *ret)
+{
+	if (*ret == -EDEADLK) {
+		if (state)
+			drm_atomic_state_clear(&state->base);
+
+		*ret = drm_modeset_backoff(ctx);
+		if (*ret == 0) {
+			*ret = -EDEADLK;
+			return;
+		}
+	}
+
+	drm_modeset_drop_locks(ctx);
+	drm_modeset_acquire_fini(ctx);
+}