soundwire: cadence: Remove wasted space in response_buf

[ Upstream commit 827c32d0df4bbe0d1c47d79f6a5eabfe9ac75216 ]

The response_buf was declared much larger (128 entries) than the number
of responses that could ever be written into it. The Cadence IP is
configurable up to a maximum of 32 entries, and the datasheet says
that RX_FIFO_AVAIL can be 2 larger than this. So allow up to 34
responses.

Also add checking in cdns_read_response() to prevent overflowing
reponse_buf if RX_FIFO_AVAIL contains an unexpectedly large number.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20221202161812.4186897-3-rf@opensource.cirrus.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/soundwire/cadence_master.h b/drivers/soundwire/cadence_master.h
index 4d1aab5b5ec2..e7f0108d417c 100644
--- a/drivers/soundwire/cadence_master.h
+++ b/drivers/soundwire/cadence_master.h
@@ -8,6 +8,12 @@
 #define SDW_CADENCE_GSYNC_KHZ		4 /* 4 kHz */
 #define SDW_CADENCE_GSYNC_HZ		(SDW_CADENCE_GSYNC_KHZ * 1000)
 
+/*
+ * The Cadence IP supports up to 32 entries in the FIFO, though implementations
+ * can configure the IP to have a smaller FIFO.
+ */
+#define CDNS_MCP_IP_MAX_CMD_LEN		32
+
 /**
  * struct sdw_cdns_pdi: PDI (Physical Data Interface) instance
  *
@@ -119,7 +125,12 @@ struct sdw_cdns {
 	struct sdw_bus bus;
 	unsigned int instance;
 
-	u32 response_buf[0x80];
+	/*
+	 * The datasheet says the RX FIFO AVAIL can be 2 entries more
+	 * than the FIFO capacity, so allow for this.
+	 */
+	u32 response_buf[CDNS_MCP_IP_MAX_CMD_LEN + 2];
+
 	struct completion tx_complete;
 	struct sdw_defer *defer;