linux-kernel - [PATCH v1] i2c: imx: fix missing stop condition in single-master mode

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Message-ID: <20241216151829.74056-1-eichest@gmail.com>
Date: Mon, 16 Dec 2024 16:16:40 +0100
From: Stefan Eichenberger <eichest@...il.com>
To: o.rempel@...gutronix.de,
	kernel@...gutronix.de,
	andi.shyti@...nel.org,
	shawnguo@...nel.org,
	s.hauer@...gutronix.de,
	festevam@...il.com,
	Frank.Li@....com,
	stefan.eichenberger@...adex.com,
	francesco.dolcini@...adex.com
Cc: linux-i2c@...r.kernel.org,
	imx@...ts.linux.dev,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v1] i2c: imx: fix missing stop condition in single-master mode

From: Stefan Eichenberger <stefan.eichenberger@...adex.com>

A regression was introduced with the implementation of single-master
mode, preventing proper stop conditions from being generated. Devices
that require a valid stop condition, such as EEPROMs, fail to function
correctly as a result.

The issue only affects devices with the single-master property enabled.

This commit resolves the issue by re-enabling I2C bus busy bit (IBB)
polling for single-master mode when generating a stop condition. The fix
further ensures that the i2c_imx->stopped flag is cleared at the start
of each transfer, allowing the stop condition to be correctly generated
in i2c_imx_stop().

According to the reference manual (IMX8MMRM, Rev. 2, 09/2019, page
5270), polling the IBB bit to determine if the bus is free is only
necessary in multi-master mode. Consequently, the IBB bit is not polled
for the start condition in single-master mode.

Fixes: 6692694aca86 ("i2c: imx: do not poll for bus busy in single master mode")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@...adex.com>
---
 drivers/i2c/busses/i2c-imx.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
index f751d231ded8..cbf66a69e20b 100644
--- a/drivers/i2c/busses/i2c-imx.c
+++ b/drivers/i2c/busses/i2c-imx.c
@@ -534,20 +534,18 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy, bool a
 {
 	unsigned long orig_jiffies = jiffies;
 	unsigned int temp;
-
-	if (!i2c_imx->multi_master)
-		return 0;
+	bool multi_master = i2c_imx->multi_master;

 	while (1) {
 		temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR);

 		/* check for arbitration lost */
-		if (temp & I2SR_IAL) {
+		if (multi_master && (temp & I2SR_IAL)) {
 			i2c_imx_clear_irq(i2c_imx, I2SR_IAL);
 			return -EAGAIN;
 		}

-		if (for_busy && (temp & I2SR_IBB)) {
+		if (for_busy && (!multi_master || (temp & I2SR_IBB))) {
 			i2c_imx->stopped = 0;
 			break;
 		}
-- 
2.45.2