openwrt/target/linux/bcm27xx/patches-5.15/950-0158-i2c-bcm2835-Set-clock-stretch-timeout-to-35ms.patch

From 0d02c918c82916059a2a68a9dfa9d426c0a1c8fa Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Fri, 12 Jul 2019 15:38:35 +0100
Subject: [PATCH] i2c: bcm2835: Set clock-stretch timeout to 35ms

The BCM2835 I2C blocks have a register to set the clock-stretch
timeout - how long the device is allowed to hold SCL low - in bus
cycles. The current driver doesn't write to the register, therefore
the default value of 64 cycles is being used for all devices.

Set the timeout to the value recommended for SMBus - 35ms.

See: https://github.com/raspberrypi/linux/issues/3064

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 drivers/i2c/busses/i2c-bcm2835.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/drivers/i2c/busses/i2c-bcm2835.c
+++ b/drivers/i2c/busses/i2c-bcm2835.c
@@ -193,6 +193,7 @@ static int clk_bcm2835_i2c_set_rate(stru
 {
 	struct clk_bcm2835_i2c *div = to_clk_bcm2835_i2c(hw);
 	u32 redl, fedl;
+	u32 clk_tout;
 	u32 divider = clk_bcm2835_i2c_calc_divider(rate, parent_rate);
 
 	if (divider == -EINVAL)
@@ -216,6 +217,17 @@ static int clk_bcm2835_i2c_set_rate(stru
 	bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_DEL,
 			   (fedl << BCM2835_I2C_FEDL_SHIFT) |
 			   (redl << BCM2835_I2C_REDL_SHIFT));
+
+	/*
+	 * Set the clock stretch timeout to the SMBUs-recommended 35ms.
+	 */
+	if (rate > 0xffff*1000/35)
+	    clk_tout = 0xffff;
+	else
+	    clk_tout = 35*rate/1000;
+
+	bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_CLKT, clk_tout);
+
 	return 0;
 }