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

drivers/gpu/drm/i915/Makefile

@@ -265,6 +265,7 @@ i915-y += \
 	display/intel_hti.o \
 	display/intel_load_detect.o \
 	display/intel_lpe_audio.o \
+	display/intel_modeset_lock.o \
 	display/intel_modeset_verify.o \
 	display/intel_modeset_setup.o \
 	display/intel_overlay.o \

drivers/gpu/drm/i915/display/intel_ddi.c

@@ -63,6 +63,7 @@
 #include "intel_hti.h"
 #include "intel_lspcon.h"
 #include "intel_mg_phy_regs.h"
+#include "intel_modeset_lock.h"
 #include "intel_pps.h"
 #include "intel_psr.h"
 #include "intel_quirks.h"
@@ -4401,26 +4402,14 @@ intel_ddi_hotplug(struct intel_encoder *encoder,
 
 	state = intel_encoder_hotplug(encoder, connector);
 
-	drm_modeset_acquire_init(&ctx, 0);
-
-	for (;;) {
+	intel_modeset_lock_ctx_retry(&ctx, NULL, 0, ret) {
 		if (connector->base.connector_type == DRM_MODE_CONNECTOR_HDMIA)
 			ret = intel_hdmi_reset_link(encoder, &ctx);
 		else
 			ret = intel_dp_retrain_link(encoder, &ctx);
-
-		if (ret == -EDEADLK) {
-			drm_modeset_backoff(&ctx);
-			continue;
-		}
-
-		break;
 	}
 
-	drm_modeset_drop_locks(&ctx);
-	drm_modeset_acquire_fini(&ctx);
-	drm_WARN(encoder->base.dev, ret,
-		 "Acquiring modeset locks failed with %i\n", ret);
+	drm_WARN_ON(encoder->base.dev, ret);
 
 	/*
 	 * Unpowered type-c dongles can take some time to boot and be

drivers/gpu/drm/i915/display/intel_modeset_lock.c

+// 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);
+}

drivers/gpu/drm/i915/display/intel_modeset_lock.h

+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2023 Intel Corporation
+ */
+
+#ifndef __INTEL_MODESET_LOCK_H__
+#define __INTEL_MODESET_LOCK_H__
+
+#include <linux/types.h>
+
+struct drm_modeset_acquire_ctx;
+struct intel_atomic_state;
+
+void _intel_modeset_lock_begin(struct drm_modeset_acquire_ctx *ctx,
+			       struct intel_atomic_state *state,
+			       unsigned int flags,
+			       int *ret);
+bool _intel_modeset_lock_loop(int *ret);
+void _intel_modeset_lock_end(struct drm_modeset_acquire_ctx *ctx,
+			     struct intel_atomic_state *state,
+			     int *ret);
+
+/*
+ * Note that one must always use "continue" rather than
+ * "break" or "return" to handle errors within the
+ * intel_modeset_lock_ctx_retry() block.
+ */
+#define intel_modeset_lock_ctx_retry(ctx, state, flags, ret) \
+	for (_intel_modeset_lock_begin((ctx), (state), (flags), &(ret)); \
+	     _intel_modeset_lock_loop(&(ret)); \
+	     _intel_modeset_lock_end((ctx), (state), &(ret)))
+
+#endif /* __INTEL_MODESET_LOCK_H__ */