drm/i915: Replace struct_mutex in intel_guc_log

Remove the use of struct_mutex from intel_guc_log.c and replace it with
a dedicated lock, guc_lock, defined within the intel_guc_log struct.
    
The struct_mutex was previously used to protect concurrent access and
modification of intel_guc_log->level in intel_guc_log_set_level().
However, it was suggested that the lock should reside within the
intel_guc_log struct itself.
    
Initialize the new guc_lock in intel_guc_log_init_early(), alongside the
existing relay.lock. The lock is initialized using drmm_mutex_init(),
which also ensures it is properly destroyed when the driver is unloaded.

Signed-off-by: Luiz Otavio Mello <luiz.mello@estudante.ufscar.br>
Suggested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20250908131518.36625-5-luiz.mello@estudante.ufscar.br
Acked-by: Tvrtko Ursulin <tursulin@ursulin.net>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Author: LuizOt31

drivers/gpu/drm/i915/gt/uc/intel_guc_log.c

@@ -518,6 +518,7 @@ void intel_guc_log_init_early(struct intel_guc_log *log)
 	struct drm_i915_private *i915 = guc_to_i915(guc);
 
 	drmm_mutex_init(&i915->drm, &log->relay.lock);
+	drmm_mutex_init(&i915->drm, &log->guc_lock);
 	INIT_WORK(&log->relay.flush_work, copy_debug_logs_work);
 	log->relay.started = false;
 }
@@ -683,7 +684,7 @@ int intel_guc_log_set_level(struct intel_guc_log *log, u32 level)
 	if (level < GUC_LOG_LEVEL_DISABLED || level > GUC_LOG_LEVEL_MAX)
 		return -EINVAL;
 
-	mutex_lock(&i915->struct_mutex);
+	mutex_lock(&log->guc_lock);
 
 	if (log->level == level)
 		goto out_unlock;
@@ -701,7 +702,7 @@ int intel_guc_log_set_level(struct intel_guc_log *log, u32 level)
 	log->level = level;
 
 out_unlock:
-	mutex_unlock(&i915->struct_mutex);
+	mutex_unlock(&log->guc_lock);
 
 	return ret;
 }

drivers/gpu/drm/i915/gt/uc/intel_guc_log.h

@@ -42,6 +42,14 @@ enum {
 struct intel_guc_log {
 	u32 level;
 
+	/*
+	 * Protects concurrent access and modification of intel_guc_log->level.
+	 *
+	 * This lock replaces the legacy struct_mutex usage in
+	 * intel_guc_log system.
+	 */
+	struct mutex guc_lock;
+
 	/* Allocation settings */
 	struct {
 		s32 bytes;	/* Size in bytes */