linux-kernel - [PATCH v2 1/2] soundwire: bus: Don't zero page registers after every transaction

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Date:   Mon, 23 Jan 2023 16:49:48 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <vkoul@...nel.org>, <yung-chuan.liao@...ux.intel.com>,
        <pierre-louis.bossart@...ux.intel.com>, <sanyog.r.kale@...el.com>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH v2 1/2] soundwire: bus: Don't zero page registers after every transaction

Zeroing the page registers at the end of every paged transaction is just
overhead (40% overhead on a 1-register access, 25% on a 4-register
transaction). According to the spec a peripheral that supports paging
should only use the values in the page registers if the address is paged
(address bit 15 set). The core SoundWire code always writes the page
registers at the start of a paged transaction so there will never be a
transaction that uses the stale values from a previous paged transaction.

For peripherals that need large amounts of data to be transferred, for
example firmware or filter coefficients, the overhead of page register
zeroing can become quite significant.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
---
 drivers/soundwire/bus.c | 23 -----------------------
 1 file changed, 23 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 633d411b64f3..b840322f7f1d 100644
--- a/drivers/soundwire/bus.c
+++ b/drivers/soundwire/bus.c
@@ -247,23 +247,6 @@ static inline int do_transfer_defer(struct sdw_bus *bus,
 	return ret;
 }
 
-static int sdw_reset_page(struct sdw_bus *bus, u16 dev_num)
-{
-	int retry = bus->prop.err_threshold;
-	enum sdw_command_response resp;
-	int ret = 0, i;
-
-	for (i = 0; i <= retry; i++) {
-		resp = bus->ops->reset_page_addr(bus, dev_num);
-		ret = find_response_code(resp);
-		/* if cmd is ok or ignored return */
-		if (ret == 0 || ret == -ENODATA)
-			return ret;
-	}
-
-	return ret;
-}
-
 static int sdw_transfer_unlocked(struct sdw_bus *bus, struct sdw_msg *msg)
 {
 	int ret;
@@ -275,9 +258,6 @@ static int sdw_transfer_unlocked(struct sdw_bus *bus, struct sdw_msg *msg)
 			(msg->flags & SDW_MSG_FLAG_WRITE) ? "write" : "read",
 			msg->addr, msg->len);
 
-	if (msg->page)
-		sdw_reset_page(bus, msg->dev_num);
-
 	return ret;
 }
 
@@ -352,9 +332,6 @@ int sdw_transfer_defer(struct sdw_bus *bus, struct sdw_msg *msg,
 		dev_err(bus->dev, "Defer trf on Slave %d failed:%d\n",
 			msg->dev_num, ret);
 
-	if (msg->page)
-		sdw_reset_page(bus, msg->dev_num);
-
 	return ret;
 }
 
-- 
2.30.2