target/linux/bcm27xx/patches-5.4/950-0268-i2c-bcm2835-Set-clock-stretch-timeout-to-35ms.patch

   1 From 9c64858d41cc65982aaf36866ffa8e04b9792718 Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.org>
   3 Date: Fri, 12 Jul 2019 15:38:35 +0100
   4 Subject: [PATCH] i2c: bcm2835: Set clock-stretch timeout to 35ms
   5
   6 The BCM2835 I2C blocks have a register to set the clock-stretch
   7 timeout - how long the device is allowed to hold SCL low - in bus
   8 cycles. The current driver doesn't write to the register, therefore
   9 the default value of 64 cycles is being used for all devices.
  10
  11 Set the timeout to the value recommended for SMBus - 35ms.
  12
  13 See: https://github.com/raspberrypi/linux/issues/3064
  14
  15 Signed-off-by: Phil Elwell <phil@raspberrypi.org>
  16 ---
  17  drivers/i2c/busses/i2c-bcm2835.c | 12 ++++++++++++
  18  1 file changed, 12 insertions(+)
  19
  20 --- a/drivers/i2c/busses/i2c-bcm2835.c
  21 +++ b/drivers/i2c/busses/i2c-bcm2835.c
  22 @@ -188,6 +188,7 @@ static int clk_bcm2835_i2c_set_rate(stru
  23  {
  24         struct clk_bcm2835_i2c *div = to_clk_bcm2835_i2c(hw);
  25         u32 redl, fedl;
  26 +       u32 clk_tout;
  27         u32 divider = clk_bcm2835_i2c_calc_divider(rate, parent_rate);
  28
  29         if (divider == -EINVAL)
  30 @@ -211,6 +212,17 @@ static int clk_bcm2835_i2c_set_rate(stru
  31         bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_DEL,
  32                            (fedl << BCM2835_I2C_FEDL_SHIFT) |
  33                            (redl << BCM2835_I2C_REDL_SHIFT));
  34 +
  35 +       /*
  36 +        * Set the clock stretch timeout to the SMBUs-recommended 35ms.
  37 +        */
  38 +       if (rate > 0xffff*1000/35)
  39 +           clk_tout = 0xffff;
  40 +       else
  41 +           clk_tout = 35*rate/1000;
  42 +
  43 +       bcm2835_i2c_writel(div->i2c_dev, BCM2835_I2C_CLKT, clk_tout);
  44 +
  45         return 0;
  46  }
  47