linux-kernel - Re: [PATCH] i2c: stm32f7: Fix PEC handling in case of SMBUS transfers

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Message-ID: <20231003174246.vdazyls3c7kykd63@zenone.zhora.eu>
Date:   Tue, 3 Oct 2023 19:42:46 +0200
From:   Andi Shyti <andi.shyti@...nel.org>
To:     Alain Volmat <alain.volmat@...s.st.com>
Cc:     Pierre-Yves MORDRET <pierre-yves.mordret@...s.st.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        M'boumba Cedric Madianga <cedric.madianga@...il.com>,
        Wolfram Sang <wsa@...nel.org>,
        Pierre-Yves MORDRET <pierre-yves.mordret@...com>,
        linux-i2c@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: stm32f7: Fix PEC handling in case of SMBUS transfers

Hi Alain,

On Mon, Oct 02, 2023 at 10:42:10AM +0200, Alain Volmat wrote:
> The PECBYTE bit allows to generate (in case of write) or
> compute/compare the PEC byte (in case of read).  In case
> of reading a value (performed by first sending a write
> command, then followed by a read command) the PECBYTE should
> only be set before starting the read command and not before
> the first write command.

What is this patch fixing?

Can you please point this detail in the documentation, I haven't
found it[*]

> Fixes: 9e48155f6bfe ("i2c: i2c-stm32f7: Add initial SMBus protocols support")
> 
> Signed-off-by: Alain Volmat <alain.volmat@...s.st.com>

please, don't leave blank lines between tags.

Thanks,
Andi

[*] Hope this is the correct one:
https://www.st.com/resource/en/reference_manual/rm0385-stm32f75xxx-and-stm32f74xxx-advanced-armbased-32bit-mcus-stmicroelectronics.pdf

> ---
>  drivers/i2c/busses/i2c-stm32f7.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
> index 579b30581725..0d3c9a041b56 100644
> --- a/drivers/i2c/busses/i2c-stm32f7.c
> +++ b/drivers/i2c/busses/i2c-stm32f7.c
> @@ -1059,9 +1059,10 @@ static int stm32f7_i2c_smbus_xfer_msg(struct stm32f7_i2c_dev *i2c_dev,
>  	/* Configure PEC */
>  	if ((flags & I2C_CLIENT_PEC) && f7_msg->size != I2C_SMBUS_QUICK) {
>  		cr1 |= STM32F7_I2C_CR1_PECEN;
> -		cr2 |= STM32F7_I2C_CR2_PECBYTE;
> -		if (!f7_msg->read_write)
> +		if (!f7_msg->read_write) {
> +			cr2 |= STM32F7_I2C_CR2_PECBYTE;
>  			f7_msg->count++;
> +		}
>  	} else {
>  		cr1 &= ~STM32F7_I2C_CR1_PECEN;
>  		cr2 &= ~STM32F7_I2C_CR2_PECBYTE;
> @@ -1149,8 +1150,10 @@ static void stm32f7_i2c_smbus_rep_start(struct stm32f7_i2c_dev *i2c_dev)
>  	f7_msg->stop = true;
>  
>  	/* Add one byte for PEC if needed */
> -	if (cr1 & STM32F7_I2C_CR1_PECEN)
> +	if (cr1 & STM32F7_I2C_CR1_PECEN) {
> +		cr2 |= STM32F7_I2C_CR2_PECBYTE;
>  		f7_msg->count++;
> +	}
>  
>  	/* Set number of bytes to be transferred */
>  	cr2 &= ~(STM32F7_I2C_CR2_NBYTES_MASK);
> -- 
> 2.25.1
>