Re: [PATCH 1/2] tpm: tis_i2c: Limit read bursts to I2C_SMBUS_BLOCK_MAX (32) bytes

[Jerry Snitselaar]

On Wed, May 24, 2023 at 05:40:39PM +0200, A. Sverdlin wrote:
> From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
> 
> Underlying I2C bus drivers not always support longer transfers and
> imx-lpi2c for instance doesn't. SLB 9673 offers 427-bytes packets.
> 
> Visible symptoms are:
> 
> tpm tpm0: Error left over data
> tpm tpm0: tpm_transmit: tpm_recv: error -5
> tpm_tis_i2c: probe of 1-002e failed with error -5
> 
> Fixes: bbc23a07b072 ("tpm: Add tpm_tis_i2c backend for tpm_tis_core")
> Tested-by: Michael Haener <michael.haener@xxxxxxxxxxx>
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>

Reviewed-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>

> ---
>  drivers/char/tpm/tpm_tis_i2c.c | 37 ++++++++++++++++++++--------------
>  1 file changed, 22 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm_tis_i2c.c b/drivers/char/tpm/tpm_tis_i2c.c
> index c8c34adc14c0..106fd20d94e4 100644
> --- a/drivers/char/tpm/tpm_tis_i2c.c
> +++ b/drivers/char/tpm/tpm_tis_i2c.c
> @@ -189,21 +189,28 @@ static int tpm_tis_i2c_read_bytes(struct tpm_tis_data *data, u32 addr, u16 len,
>  	int ret;
>  
>  	for (i = 0; i < TPM_RETRY; i++) {
> -		/* write register */
> -		msg.len = sizeof(reg);
> -		msg.buf = &reg;
> -		msg.flags = 0;
> -		ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
> -		if (ret < 0)
> -			return ret;
> -
> -		/* read data */
> -		msg.buf = result;
> -		msg.len = len;
> -		msg.flags = I2C_M_RD;
> -		ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
> -		if (ret < 0)
> -			return ret;
> +		u16 read = 0;
> +
> +		while (read < len) {
> +			/* write register */
> +			msg.len = sizeof(reg);
> +			msg.buf = &reg;
> +			msg.flags = 0;
> +			ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
> +			if (ret < 0)
> +				return ret;
> +
> +			/* read data */
> +			msg.buf = result + read;
> +			msg.len = len - read;
> +			msg.flags = I2C_M_RD;
> +			if (msg.len > I2C_SMBUS_BLOCK_MAX)
> +				msg.len = I2C_SMBUS_BLOCK_MAX;
> +			ret = tpm_tis_i2c_retry_transfer_until_ack(data, &msg);
> +			if (ret < 0)
> +				return ret;
> +			read += msg.len;
> +		}
>  
>  		ret = tpm_tis_i2c_sanity_check_read(reg, len, result);
>  		if (ret == 0)
> -- 
> 2.40.1
>