linux-kernel - [PATCH v2 2/5] i2c: designware: Optimize flag reading in i2c_dw

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Message-Id: <20251031-i2c-dw-v2-2-90416874fcc0@bootlin.com>
Date: Fri, 31 Oct 2025 15:35:40 +0100
From: Benoît Monin <benoit.monin@...tlin.com>
To: Andi Shyti <andi.shyti@...nel.org>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Jarkko Nikula <jarkko.nikula@...ux.intel.com>, 
 Mika Westerberg <mika.westerberg@...ux.intel.com>, 
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
 Jan Dabros <jsd@...ihalf.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 Clark Williams <clrkwllms@...nel.org>, Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>, 
 Gregory CLEMENT <gregory.clement@...tlin.com>, 
 Théo Lebrun <theo.lebrun@...tlin.com>, 
 Tawfik Bayouk <tawfik.bayouk@...ileye.com>, 
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>, 
 Dmitry Guzman <dmitry.guzman@...ileye.com>, linux-i2c@...r.kernel.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-rt-devel@...ts.linux.dev, 
 Benoît Monin <benoit.monin@...tlin.com>
Subject: [PATCH v2 2/5] i2c: designware: Optimize flag reading in
 i2c_dw_read()

Optimize the i2c_dw_read() function by reading the message flags only
once per message, rather than for every byte.

The message index is only modified by the outer loop, so reading the
flags in the inner loop was always getting the same value.

Signed-off-by: Benoît Monin <benoit.monin@...tlin.com>
---
 drivers/i2c/busses/i2c-designware-master.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
index 41e9b5ecad20..ec4fc2708d03 100644
--- a/drivers/i2c/busses/i2c-designware-master.c
+++ b/drivers/i2c/busses/i2c-designware-master.c
@@ -586,11 +586,12 @@ i2c_dw_read(struct dw_i2c_dev *dev)
 	unsigned int rx_valid;
 
 	for (; dev->msg_read_idx < dev->msgs_num; dev->msg_read_idx++) {
+		u32 flags = msgs[dev->msg_read_idx].flags;
 		unsigned int tmp;
 		u32 len;
 		u8 *buf;
 
-		if (!(msgs[dev->msg_read_idx].flags & I2C_M_RD))
+		if (!(flags & I2C_M_RD))
 			continue;
 
 		if (!(dev->status & STATUS_READ_IN_PROGRESS)) {
@@ -604,8 +605,6 @@ i2c_dw_read(struct dw_i2c_dev *dev)
 		regmap_read(dev->map, DW_IC_RXFLR, &rx_valid);
 
 		for (; len > 0 && rx_valid > 0; len--, rx_valid--) {
-			u32 flags = msgs[dev->msg_read_idx].flags;
-
 			regmap_read(dev->map, DW_IC_DATA_CMD, &tmp);
 			tmp &= DW_IC_DATA_CMD_DAT;
 			/* Ensure length byte is a valid value */

-- 
2.51.1