[PATCH v5 24/25] soundwire: amd: fix shared-register RMW race in amd_sdw_set_device_state()

[Vijendar Mukunda]

AMD_SDW_DEVICE_STATE packs the D0/D3 state for SDW0 (bits [1:0]) and
SDW1 (bits [3:2]) in a single ACP-level register.
amd_sdw_set_device_state() performed a read-modify-write sequence on
this shared register without holding acp_sdw_lock, leaving it open to
a lost-update race when SDW0 and SDW1 execute concurrent PM transitions.

Acquire acp_sdw_lock around the read-modify-write sequence. Unlock
before returning -EINVAL from the default branch so the mutex is always
released on every exit path.

Fixes: 829c3e1cb4a3 ("soundwire: amd: set device power state during suspend/resume sequence")
Signed-off-by: Vijendar Mukunda <Vijendar.Mukunda@xxxxxxx>
---
 drivers/soundwire/amd_manager.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/soundwire/amd_manager.c b/drivers/soundwire/amd_manager.c
index 4e151f7350c9..495f0607bb0b 100644
--- a/drivers/soundwire/amd_manager.c
+++ b/drivers/soundwire/amd_manager.c
@@ -279,6 +279,7 @@ static int amd_sdw_set_device_state(struct amd_sdw_manager *amd_manager, u32 tar
 {
 	u32 sdw_dev_state;
 
+	mutex_lock(amd_manager->acp_sdw_lock);
 	sdw_dev_state = readl(amd_manager->acp_mmio + AMD_SDW_DEVICE_STATE);
 	switch (amd_manager->instance) {
 	case ACP_SDW0:
@@ -290,10 +291,12 @@ static int amd_sdw_set_device_state(struct amd_sdw_manager *amd_manager, u32 tar
 				  AMD_SDW1_DEVICE_STATE_MASK);
 		break;
 	default:
+		mutex_unlock(amd_manager->acp_sdw_lock);
 		return -EINVAL;
 	}
 	writel(sdw_dev_state, amd_manager->acp_mmio + AMD_SDW_DEVICE_STATE);
 	sdw_dev_state = readl(amd_manager->acp_mmio + AMD_SDW_DEVICE_STATE);
+	mutex_unlock(amd_manager->acp_sdw_lock);
 	dev_dbg(amd_manager->dev, "AMD_SDW_DEVICE_STATE:0x%x\n", sdw_dev_state);
 	return 0;
 }
-- 
2.53.0