i2c: stm32f7: fix timing computation ignoring i2c-analog-filter

[PATCH] i2c: stm32f7: fix timing computation ignoring i2c-analog-filter

Posted by Guillermo Rodríguez 1 week, 6 days ago

stm32f7_i2c_compute_timing() uses i2c_dev->analog_filter to pick
the analog filter delay, but i2c_dev->analog_filter is parsed from
the "i2c-analog-filter" DT property only after the compute_timing
loop in stm32f7_i2c_setup_timing(), so in practice the timing
calculations always ignore the analog filter. On an STM32MP1 board
with clock-frequency = <400000> and i2c-analog-filter set, measured
SCL frequency was ~382 kHz.

This also affects (widens) the computed SDADEL range. At high bus
clock speeds, this can select an SDADEL value that violates tVD;DAT
(data valid time).

Fix by parsing "i2c-analog-filter" before the compute_timing loop.

Fixes: 83c3408f7b9c ("i2c: stm32f7: support DT binding i2c-analog-filter")
Cc: stable@vger.kernel.org
Signed-off-by: Guillermo Rodríguez <guille.rodriguez@gmail.com>
---
 drivers/i2c/busses/i2c-stm32f7.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
index 53d9df70ebe4..067af255bd22 100644
--- a/drivers/i2c/busses/i2c-stm32f7.c
+++ b/drivers/i2c/busses/i2c-stm32f7.c
@@ -694,6 +694,9 @@ static int stm32f7_i2c_setup_timing(struct stm32f7_i2c_dev *i2c_dev,
 	if (!of_property_read_bool(i2c_dev->dev->of_node, "i2c-digital-filter"))
 		i2c_dev->dnf_dt = STM32F7_I2C_DNF_DEFAULT;
 
+	i2c_dev->analog_filter = of_property_read_bool(i2c_dev->dev->of_node,
+						       "i2c-analog-filter");
+
 	do {
 		ret = stm32f7_i2c_compute_timing(i2c_dev, setup,
 						 &i2c_dev->timing);
@@ -715,9 +718,6 @@ static int stm32f7_i2c_setup_timing(struct stm32f7_i2c_dev *i2c_dev,
 		return ret;
 	}
 
-	i2c_dev->analog_filter = of_property_read_bool(i2c_dev->dev->of_node,
-						       "i2c-analog-filter");
-
 	dev_dbg(i2c_dev->dev, "I2C Speed(%i), Clk Source(%i)\n",
 		setup->speed_freq, setup->clock_src);
 	dev_dbg(i2c_dev->dev, "I2C Rise(%i) and Fall(%i) Time\n",
-- 
2.25.1

Re: [PATCH] i2c: stm32f7: fix timing computation ignoring i2c-analog-filter

Posted by Andi Shyti 2 hours ago

Hi Guillermo,

On Tue, May 26, 2026 at 11:12:09AM +0200, Guillermo Rodríguez wrote:
> stm32f7_i2c_compute_timing() uses i2c_dev->analog_filter to pick
> the analog filter delay, but i2c_dev->analog_filter is parsed from
> the "i2c-analog-filter" DT property only after the compute_timing
> loop in stm32f7_i2c_setup_timing(), so in practice the timing
> calculations always ignore the analog filter. On an STM32MP1 board
> with clock-frequency = <400000> and i2c-analog-filter set, measured
> SCL frequency was ~382 kHz.
> 
> This also affects (widens) the computed SDADEL range. At high bus
> clock speeds, this can select an SDADEL value that violates tVD;DAT
> (data valid time).
> 
> Fix by parsing "i2c-analog-filter" before the compute_timing loop.
> 
> Fixes: 83c3408f7b9c ("i2c: stm32f7: support DT binding i2c-analog-filter")
> Cc: stable@vger.kernel.org
> Signed-off-by: Guillermo Rodríguez <guille.rodriguez@gmail.com>

merged to i2c/i2c-host-fixes.

Thanks,
Andi

Re: [PATCH] i2c: stm32f7: fix timing computation ignoring i2c-analog-filter

Posted by Alain Volmat 5 days, 11 hours ago

Hi,

thank you for you patch.

On Tue, May 26, 2026 at 11:12:09AM +0200, Guillermo Rodríguez wrote:
> stm32f7_i2c_compute_timing() uses i2c_dev->analog_filter to pick
> the analog filter delay, but i2c_dev->analog_filter is parsed from
> the "i2c-analog-filter" DT property only after the compute_timing
> loop in stm32f7_i2c_setup_timing(), so in practice the timing
> calculations always ignore the analog filter. On an STM32MP1 board
> with clock-frequency = <400000> and i2c-analog-filter set, measured
> SCL frequency was ~382 kHz.
> 
> This also affects (widens) the computed SDADEL range. At high bus
> clock speeds, this can select an SDADEL value that violates tVD;DAT
> (data valid time).
> 
> Fix by parsing "i2c-analog-filter" before the compute_timing loop.
> 
> Fixes: 83c3408f7b9c ("i2c: stm32f7: support DT binding i2c-analog-filter")
> Cc: stable@vger.kernel.org
> Signed-off-by: Guillermo Rodríguez <guille.rodriguez@gmail.com>
> ---
>  drivers/i2c/busses/i2c-stm32f7.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
> index 53d9df70ebe4..067af255bd22 100644
> --- a/drivers/i2c/busses/i2c-stm32f7.c
> +++ b/drivers/i2c/busses/i2c-stm32f7.c
> @@ -694,6 +694,9 @@ static int stm32f7_i2c_setup_timing(struct stm32f7_i2c_dev *i2c_dev,
>  	if (!of_property_read_bool(i2c_dev->dev->of_node, "i2c-digital-filter"))
>  		i2c_dev->dnf_dt = STM32F7_I2C_DNF_DEFAULT;
>  
> +	i2c_dev->analog_filter = of_property_read_bool(i2c_dev->dev->of_node,
> +						       "i2c-analog-filter");
> +
>  	do {
>  		ret = stm32f7_i2c_compute_timing(i2c_dev, setup,
>  						 &i2c_dev->timing);
> @@ -715,9 +718,6 @@ static int stm32f7_i2c_setup_timing(struct stm32f7_i2c_dev *i2c_dev,
>  		return ret;
>  	}
>  
> -	i2c_dev->analog_filter = of_property_read_bool(i2c_dev->dev->of_node,
> -						       "i2c-analog-filter");
> -
>  	dev_dbg(i2c_dev->dev, "I2C Speed(%i), Clk Source(%i)\n",
>  		setup->speed_freq, setup->clock_src);
>  	dev_dbg(i2c_dev->dev, "I2C Rise(%i) and Fall(%i) Time\n",
> -- 
> 2.25.1
> 

Acked-by: Alain Volmat <alain.volmat@foss.st.com>

Regards,
Alain