[PATCH] i2c: bcm2835: Set clock-stretch timeout to 35ms

[Ivan T . Ivanov]

On 01-17 11:25, Ivan T. Ivanov wrote:
> Date: Mon, 17 Jan 2022 11:25:04 +0100
> From: "Ivan T. Ivanov" <iivanov at suse.de>
> To: Florian Fainelli <f.fainelli at gmail.com>, Ray Jui <rjui at broadcom.com>,
>  Scott Branden <sbranden at broadcom.com>, Nicolas Saenz Julienne
>  <nsaenz at kernel.org>
> Cc: linux-i2c at vger.kernel.org, linux-arm-kernel at lists.infradead.org, Phil
>  Elwell <phil at raspberrypi.org>, "Ivan T . Ivanov" <iivanov at suse.de>
> Subject: [PATCH] i2c: bcm2835: Set clock-stretch timeout to 35ms
> Message-Id: <20220117102504.90585-1-iivanov at suse.de>
Tags: all arm i2c linux me ring rpi sent

Hi,

> 
> From: Phil Elwell <phil at raspberrypi.org>
> 
> 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

It will be nice if we have this fix upstream.

Regards,
Ivan

> 
> Signed-off-by: Phil Elwell <phil at raspberrypi.org>
> [iivanov at suse.de fix small coding style issue]
> Signed-off-by: Ivan T. Ivanov <iivanov at suse.de>
> ---
>  drivers/i2c/busses/i2c-bcm2835.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c
> index 37443edbf754..9cce0e15da32 100644
> --- a/drivers/i2c/busses/i2c-bcm2835.c
> +++ b/drivers/i2c/busses/i2c-bcm2835.c
> @@ -106,6 +106,7 @@ static int clk_bcm2835_i2c_set_rate(struct clk_hw *hw, unsigned long rate,
>  {
>  	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)
> @@ -129,6 +130,17 @@ static int clk_bcm2835_i2c_set_rate(struct clk_hw *hw, unsigned long rate,
>  	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;
>  }
>  
> -- 
> 2.26.2
>