From 9495b9b31abe525ebd93da58de2c88b9f66d3a0e Mon Sep 17 00:00:00 2001
From: Eric Anholt <eric@anholt.net>
Date: Fri, 23 Feb 2018 22:42:31 +0100
Subject: [PATCH] i2c: bcm2835: Avoid clock stretching timeouts
Git-commit: 9495b9b31abe525ebd93da58de2c88b9f66d3a0e
Patch-mainline: v5.17-rc5
References: git-fixes

The CLKT register contains at poweron 0x40, which at our typical 100kHz
bus rate means .64ms. But there is no specified limit to how long devices
should be able to stretch the clocks, so just disable the timeout. We
still have a timeout wrapping the entire transfer.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Buglink: https://github.com/raspberrypi/linux/issues/3064
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/i2c/busses/i2c-bcm2835.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
index dfc534065595..5149454eef4a 100644
--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -23,6 +23,11 @@
 #define BCM2835_I2C_FIFO	0x10
 #define BCM2835_I2C_DIV		0x14
 #define BCM2835_I2C_DEL		0x18
+/*
+ * 16-bit field for the number of SCL cycles to wait after rising SCL
+ * before deciding the slave is not responding. 0 disables the
+ * timeout detection.
+ */
 #define BCM2835_I2C_CLKT	0x1c
 
 #define BCM2835_I2C_C_READ	BIT(0)
@@ -474,6 +479,12 @@ static int bcm2835_i2c_probe(struct platform_device *pdev)
 	adap->dev.of_node = pdev->dev.of_node;
 	adap->quirks = of_device_get_match_data(&pdev->dev);
 
+	/*
+	 * Disable the hardware clock stretching timeout. SMBUS
+	 * specifies a limit for how long the device can stretch the
+	 * clock, but core I2C doesn't.
+	 */
+	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_CLKT, 0);
 	bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);
 
 	ret = i2c_add_adapter(adap);
-- 
2.31.1