[PATCH 2/8] soundwire: amd: cache ping slave status to avoid spurious disconnect on timeout

[Vijendar Mukunda]

Add ping_slave_stat to struct amd_sdw_manager to cache the slave_stat
from the last successful ping response. On timeout,
amd_sdw_read_ping_status() returns the cached value (or 0 if no
successful response yet) to avoid the spurious "no peripherals
attached" warning from sdw_show_ping_status().

ping_slave_stat is initialised to U32_MAX in probe and reset to
U32_MAX under msg_lock on entry to the POWER_OFF_MODE resume path,
before any hardware step that can fail and return early, so that a
partially-failed resume cannot leave a stale pre-suspend value behind
for a subsequent ping timeout to report.

Add lockdep_assert_held() in amd_sdw_read_ping_status() to document
that the caller must hold msg_lock.

Signed-off-by: Vijendar Mukunda <Vijendar.Mukunda@xxxxxxx>
---
 drivers/soundwire/amd_manager.c   | 21 ++++++++++++++++++++-
 include/linux/soundwire/sdw_amd.h |  3 +++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/amd_manager.c b/drivers/soundwire/amd_manager.c
index fa3f4e797edd..a57b59609bfe 100644
--- a/drivers/soundwire/amd_manager.c
+++ b/drivers/soundwire/amd_manager.c
@@ -453,6 +453,9 @@ static void amd_sdw_read_and_process_ping_status(struct amd_sdw_manager *amd_man
 				    amd_manager->instance);
 		return;
 	}
+	amd_manager->ping_slave_stat =
+		FIELD_GET(AMD_SDW_MCP_SLAVE_STAT_0_3, response) |
+		(FIELD_GET(AMD_SDW_MCP_SLAVE_STAT_4_11, response) << 8);
 	amd_sdw_process_ping_status(response, amd_manager);
 	mutex_unlock(&amd_manager->bus.msg_lock);
 }
@@ -463,15 +466,19 @@ static u32 amd_sdw_read_ping_status(struct sdw_bus *bus)
 	u64 response;
 	u32 slave_stat;
 
+	/* Called by sdw_show_ping_status() which holds msg_lock. */
+	lockdep_assert_held(&bus->msg_lock);
+
 	if (amd_sdw_send_cmd_get_resp(amd_manager, 0, 0, &response)) {
 		dev_err_ratelimited(amd_manager->dev, "SDW%x ping status timeout\n",
 				    amd_manager->instance);
-		return 0;
+		return amd_manager->ping_slave_stat == U32_MAX ? 0 : amd_manager->ping_slave_stat;
 	}
 	/* slave status from ping response */
 	slave_stat = FIELD_GET(AMD_SDW_MCP_SLAVE_STAT_0_3, response);
 	slave_stat |= FIELD_GET(AMD_SDW_MCP_SLAVE_STAT_4_11, response) << 8;
 	dev_dbg(amd_manager->dev, "slave_stat:0x%x\n", slave_stat);
+	amd_manager->ping_slave_stat = slave_stat;
 	return slave_stat;
 }
 
@@ -1087,6 +1094,7 @@ static int amd_sdw_manager_probe(struct platform_device *pdev)
 		dev_err(dev, "mmio not found\n");
 		return -ENOMEM;
 	}
+	amd_manager->ping_slave_stat = U32_MAX;
 	amd_manager->instance = pdata->instance;
 	amd_manager->mmio = amd_manager->acp_mmio +
 			    (amd_manager->instance * SDW_MANAGER_REG_OFFSET);
@@ -1414,6 +1422,17 @@ static int __maybe_unused amd_resume_runtime(struct device *dev)
 		}
 	} else if (amd_manager->power_mode_mask & AMD_SDW_POWER_OFF_MODE) {
 		writel(0x00, amd_manager->acp_mmio + ACP_SW_WAKE_EN(amd_manager->instance));
+		/*
+		 * POWER_OFF_MODE tears the bus down completely; invalidate the
+		 * cached ping status on entry, before any step that can fail and
+		 * return early, so that a partially-failed resume leaves the first
+		 * post-resume ping timeout returning 0 rather than stale
+		 * pre-suspend data. CLK_STOP_MODE leaves peripherals attached, so
+		 * the cache remains valid there.
+		 */
+		mutex_lock(&amd_manager->bus.msg_lock);
+		amd_manager->ping_slave_stat = U32_MAX;
+		mutex_unlock(&amd_manager->bus.msg_lock);
 		if (amd_manager->acp_rev >= ACP70_PCI_REV_ID) {
 			ret = amd_sdw_host_wake_enable(amd_manager, false);
 			if (ret)
diff --git a/include/linux/soundwire/sdw_amd.h b/include/linux/soundwire/sdw_amd.h
index 470360a2723c..12537904e34a 100644
--- a/include/linux/soundwire/sdw_amd.h
+++ b/include/linux/soundwire/sdw_amd.h
@@ -76,6 +76,8 @@ struct sdw_amd_dai_runtime {
  * @acp_rev: acp pci device revision id
  * @clk_stopped: flag set to true when clock is stopped
  * @power_mode_mask: flag interprets amd SoundWire manager power mode
+ * @ping_slave_stat: cached slave status from the last successful ping response;
+ *                   initialised to U32_MAX ("no valid reading yet")
  * @dai_runtime_array: dai runtime array
  */
 struct amd_sdw_manager {
@@ -105,6 +107,7 @@ struct amd_sdw_manager {
 	u32 wake_en_mask;
 	u32 power_mode_mask;
 	u32 acp_rev;
+	u32 ping_slave_stat;
 	bool clk_stopped;
 
 	struct sdw_amd_dai_runtime **dai_runtime_array;
-- 
2.48.1