linux-kernel - Re: [PATCH] i2c: designware: Get right data length

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Date:   Thu, 25 Feb 2021 13:19:55 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Liguang Zhang <zhangliguang@...ux.alibaba.com>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: designware: Get right data length

On Thu, Feb 25, 2021 at 10:35:28AM +0800, Liguang Zhang wrote:
> IC_DATA_CMD[11] indicates the first data byte received after the address
> phase for receive transfer in Master receiver or Slave receiver mode,
> this bit was set in some transfer flow. IC_DATA_CMD[7:0] contains the
> data to be transmitted or received on the I2C bus, so we should use the
> lower 8 bits to get the right data length.

Thanks for the report and fix!
My comments below.

> Signed-off-by: Liguang Zhang <zhangliguang@...ux.alibaba.com>
> ---
>  drivers/i2c/busses/i2c-designware-master.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-master.c b/drivers/i2c/busses/i2c-designware-master.c
> index d6425ad6e6a3..c3cf76f6c607 100644
> --- a/drivers/i2c/busses/i2c-designware-master.c
> +++ b/drivers/i2c/busses/i2c-designware-master.c
> @@ -432,7 +432,7 @@ i2c_dw_read(struct dw_i2c_dev *dev)
>  			regmap_read(dev->map, DW_IC_DATA_CMD, &tmp);
>  			/* Ensure length byte is a valid value */
>  			if (flags & I2C_M_RECV_LEN &&
> -			    tmp <= I2C_SMBUS_BLOCK_MAX && tmp > 0) {
> +			    (tmp & 0xff) <= I2C_SMBUS_BLOCK_MAX && tmp > 0) {

Can we rather describe this as

#define DW_IC_DATA_CMD_DAT   GENMASK(7, 0)

in *.h file and...

			    (tmp & DW_IC_DATA_CMD_DAT) <= I2C_SMBUS_BLOCK_MAX && tmp > 0) {
...here?

>  				len = i2c_dw_recv_len(dev, tmp);
>  			}
>  			*buf++ = tmp;
> -- 
> 2.19.1.6.gb485710b
> 

-- 
With Best Regards,
Andy Shevchenko