drm/i915: split out i915_timer_util.[ch]

Move timer related utilities from i915_utils.[ch] to separate new files
i915_timer_util.[ch]. Clean up related includes.

Note: Arguably none of this should exist in i915 in the first place. At
least isolate it better.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/0a83d9489626121dcefcd4c1a05317399b5708f3.1757582214.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/i915_timer_util.c b/drivers/gpu/drm/i915/i915_timer_util.c
new file mode 100644
index 000000000000..ee4cfd8b3c07
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_timer_util.c
@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: MIT
+/* Copyright © 2025 Intel Corporation */
+
+#include <linux/jiffies.h>
+
+#include "i915_timer_util.h"
+
+void cancel_timer(struct timer_list *t)
+{
+	if (!timer_active(t))
+		return;
+
+	timer_delete(t);
+	WRITE_ONCE(t->expires, 0);
+}
+
+void set_timer_ms(struct timer_list *t, unsigned long timeout)
+{
+	if (!timeout) {
+		cancel_timer(t);
+		return;
+	}
+
+	timeout = msecs_to_jiffies(timeout);
+
+	/*
+	 * Paranoia to make sure the compiler computes the timeout before
+	 * loading 'jiffies' as jiffies is volatile and may be updated in
+	 * the background by a timer tick. All to reduce the complexity
+	 * of the addition and reduce the risk of losing a jiffy.
+	 */
+	barrier();
+
+	/* Keep t->expires = 0 reserved to indicate a canceled timer. */
+	mod_timer(t, jiffies + timeout ?: 1);
+}