[PATCH 2/3] soundwire: cadence: Remove wasted space in response_buf

[Richard Fitzgerald <rf@opensource.cirrus.com>]

The response_buf was declared much larger (128 entries) than the number
of responses that could ever be written into it (maximum 8).

Reduce response_buf to 8 entries and add checking in cdns_read_response()
to prevent overflowing reponse_buf if CDNS_MCP_RX_FIFO_AVAIL contains
an unexpectedly large number.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
---
 drivers/soundwire/cadence_master.c | 6 ++++++
 drivers/soundwire/cadence_master.h | 2 +-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
index 27699f341f2c..95c84d9f0775 100644
--- a/drivers/soundwire/cadence_master.c
+++ b/drivers/soundwire/cadence_master.c
@@ -774,8 +774,14 @@ static void cdns_read_response(struct sdw_cdns *cdns)
 	u32 num_resp, cmd_base;
 	int i;
 
+	BUILD_BUG_ON(ARRAY_SIZE(cdns->response_buf) < CDNS_MCP_CMD_LEN);
+
 	num_resp = cdns_readl(cdns, CDNS_MCP_FIFOSTAT);
 	num_resp &= CDNS_MCP_RX_FIFO_AVAIL;
+	if (num_resp > ARRAY_SIZE(cdns->response_buf)) {
+		dev_warn(cdns->dev, "RX AVAIL %d too long\n", num_resp);
+		num_resp = CDNS_MCP_CMD_LEN;
+	}
 
 	cmd_base = CDNS_MCP_CMD_BASE;
 
diff --git a/drivers/soundwire/cadence_master.h b/drivers/soundwire/cadence_master.h
index 0434d70d4b1f..c2d817e8e22a 100644
--- a/drivers/soundwire/cadence_master.h
+++ b/drivers/soundwire/cadence_master.h
@@ -117,7 +117,7 @@ struct sdw_cdns {
 	struct sdw_bus bus;
 	unsigned int instance;
 
-	u32 response_buf[0x80];
+	u32 response_buf[8];
 	struct completion tx_complete;
 	struct sdw_defer *defer;
 
-- 
2.30.2