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

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Date:   Thu, 1 Dec 2022 14:08:12 +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 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 the peripheral should only use the
values in the page registers if the address is paged, and since the page
registers are always overwritten at the start of a paged transaction 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>
---
 drivers/soundwire/bus.c | 23 -----------------------
 1 file changed, 23 deletions(-)

diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
index 76515c33e639..a02edcbfc282 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