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

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

[Ivan T. Ivanov]

From: Phil Elwell <phil@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

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
[iivanov@suse.de fix small coding style issue]
Signed-off-by: Ivan T. Ivanov <iivanov@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

Re: [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@suse.de>
> To: Florian Fainelli <f.fainelli@gmail.com>, Ray Jui <rjui@broadcom.com>,
>  Scott Branden <sbranden@broadcom.com>, Nicolas Saenz Julienne
>  <nsaenz@kernel.org>
> Cc: linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Phil
>  Elwell <phil@raspberrypi.org>, "Ivan T . Ivanov" <iivanov@suse.de>
> Subject: [PATCH] i2c: bcm2835: Set clock-stretch timeout to 35ms
> Message-Id: <20220117102504.90585-1-iivanov@suse.de>
Tags: all arm i2c linux me ring rpi sent

Hi,

> 
> From: Phil Elwell <phil@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@raspberrypi.org>
> [iivanov@suse.de fix small coding style issue]
> Signed-off-by: Ivan T. Ivanov <iivanov@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
> 

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

[Wolfram Sang]

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Hi Ivan,

> 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.

By default, busses are I2C and not SMBus, so it looks like we should
finally apply this patch which disables CLKT:

http://patchwork.ozlabs.org/project/linux-i2c/patch/1519422151-6218-1-git-send-email-stefan.wahren@i2se.com/

If you really want the SMBus timeout applied, you can check for a
"smbus" property in DT and then set CLKT accordingly in a seperate
patch.

Kind regards,

   Wolfram


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

[Wolfram Sang]

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> By default, busses are I2C and not SMBus, so it looks like we should
> finally apply this patch which disables CLKT:
> 
> http://patchwork.ozlabs.org/project/linux-i2c/patch/1519422151-6218-1-git-send-email-stefan.wahren@i2se.com/

I applied this now to for-current and added stable. That should avoid
unwanted timeouts.

> If you really want the SMBus timeout applied, you can check for a
> "smbus" property in DT and then set CLKT accordingly in a seperate
> patch.

This still holds.


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

[Ivan T. Ivanov]

On 02-07 16:15, Wolfram Sang wrote:
> Date: Mon, 7 Feb 2022 16:15:24 +0100
> From: Wolfram Sang <wsa@kernel.org>
> To: "Ivan T. Ivanov" <iivanov@suse.de>, Florian Fainelli
>  <f.fainelli@gmail.com>, Ray Jui <rjui@broadcom.com>, Scott Branden
>  <sbranden@broadcom.com>, Nicolas Saenz Julienne <nsaenz@kernel.org>,
>  linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Phil
>  Elwell <phil@raspberrypi.org>
> Subject: Re: [PATCH] i2c: bcm2835: Set clock-stretch timeout to 35ms
> Message-ID: <YgE3jMkzisFZFHb5@shikoro>
Tags: all arm i2c linux me ring rpi
> 
> 
> > By default, busses are I2C and not SMBus, so it looks like we should
> > finally apply this patch which disables CLKT:
> > 
> > http://patchwork.ozlabs.org/project/linux-i2c/patch/1519422151-6218-1-git-send-email-stefan.wahren@i2se.com/
> 
> I applied this now to for-current and added stable. That should avoid
> unwanted timeouts.

Thanks! Unfortunately reporter went silent after I have prepared for him
kernel package with _this_ patch [1], so it will be difficult to verify
above change on my side.

> 
> > If you really want the SMBus timeout applied, you can check for a
> > "smbus" property in DT and then set CLKT accordingly in a seperate
> > patch.
> 
> This still holds.

Sure, will keep it in mind.

Regards,
Ivan

[1] https://bugzilla.suse.com/show_bug.cgi?id=1192976