linux-kernel - [PATCH v2 1/3] soundwire: cadence: Don't overflow the command FIFOs

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Date:   Fri, 2 Dec 2022 16:18:10 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <vkoul@...nel.org>, <pierre-louis.bossart@...ux.intel.com>
CC:     <yung-chuan.liao@...ux.intel.com>, <sanyog.r.kale@...el.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH v2 1/3] soundwire: cadence: Don't overflow the command FIFOs

The command FIFOs in the Cadence IP can be configured during design
up to 32 entries, and the code in cadence_master.c was assuming the
full 32-entry FIFO. But all current Intel implementations use an 8-entry
FIFO.

Up to now the longest message used was 6 entries so this wasn't
causing any problem. But future Cirrus Logic codecs have downloadable
firmware or tuning blobs. It is more efficient for the codec driver to
issue long transfers that can take advantage of any queuing in the
Soundwire controller and avoid the overhead of repeatedly writing the
page registers.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Fixes: 2f52a5177caa ("soundwire: cdns: Add cadence library")
---
Changes since v1:
Commit description rewritten. No code change.
---
 drivers/soundwire/cadence_master.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
index a1de363eba3f..27699f341f2c 100644
--- a/drivers/soundwire/cadence_master.c
+++ b/drivers/soundwire/cadence_master.c
@@ -127,7 +127,8 @@ MODULE_PARM_DESC(cdns_mcp_int_mask, "Cadence MCP IntMask");
 
 #define CDNS_MCP_CMD_BASE			0x80
 #define CDNS_MCP_RESP_BASE			0x80
-#define CDNS_MCP_CMD_LEN			0x20
+/* FIFO can hold 8 commands */
+#define CDNS_MCP_CMD_LEN			8
 #define CDNS_MCP_CMD_WORD_LEN			0x4
 
 #define CDNS_MCP_CMD_SSP_TAG			BIT(31)
-- 
2.30.2