[PATCH v4 15/21] wifi: mt76: mt792x: fix firmware reload failure after previous load crash

[Zac]

From: Zac Bowling <zbowling at gmail.com>

If the firmware loading process crashes or is interrupted after
acquiring the patch semaphore but before releasing it, subsequent
firmware load attempts will fail with 'Failed to get patch semaphore'
because the semaphore is still held.

This issue manifests as devices becoming unusable after suspend/resume
failures or firmware crashes, requiring a full hardware reboot to
recover. This has been widely reported on MT7921 and MT7925 devices.

Example error log:
  mt7921e 0000:c2:00.0: Failed to get patch semaphore
  mt7921e 0000:c2:00.0: probe with driver mt7921e failed with error -5

Apply the same fix that was applied to MT7915 in commit 79dd14f:
1. Release the patch semaphore before starting firmware load (in case
   it was held by a previous failed attempt)
2. Restart MCU firmware to ensure clean state
3. Wait briefly for MCU to be ready

This fix applies to both MT7921 and MT7925 drivers which share the
mt792x_load_firmware() function.

Fixes: 583204ae70f9 ("wifi: mt76: mt792x: move mt7921_load_firmware in mt792x-lib module")
Link: https://github.com/openwrt/mt76/commit/79dd14f2e8161b656341b6653261779199aedbe4
Signed-off-by: Zac Bowling <zac at zacbowling.com>
---
 drivers/net/wireless/mediatek/mt76/mt792x_core.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/drivers/net/wireless/mediatek/mt76/mt792x_core.c b/drivers/net/wireless/mediatek/mt76/mt792x_core.c
index 9dc768aa8b..05598202b4 100644
--- a/drivers/net/wireless/mediatek/mt76/mt792x_core.c
+++ b/drivers/net/wireless/mediatek/mt76/mt792x_core.c
@@ -936,6 +936,20 @@ int mt792x_load_firmware(struct mt792x_dev *dev)
 {
 	int ret;
 
+	/* Release semaphore if taken by previous failed load attempt.
+	 * This prevents "Failed to get patch semaphore" errors when
+	 * recovering from firmware crashes or suspend/resume failures.
+	 */
+	ret = mt76_connac_mcu_patch_sem_ctrl(&dev->mt76, false);
+	if (ret < 0)
+		dev_dbg(dev->mt76.dev, "Semaphore release returned %d (may be expected)\n", ret);
+
+	/* Always restart MCU to ensure clean state before loading firmware */
+	mt76_connac_mcu_restart(&dev->mt76);
+
+	/* Wait for MCU to be ready after restart */
+	msleep(100);
+
 	ret = mt76_connac2_load_patch(&dev->mt76, mt792x_patch_name(dev));
 	if (ret)
 		return ret;
-- 
2.52.0