[PATCH] soundwire: cadence: Don't overwrite msg->buf during write commands

[Pierre-Louis Bossart]

On 9/16/22 12:35, Richard Fitzgerald wrote:
> The buf passed in struct sdw_msg must only be written for a READ,
> in that case the RDATA part of the response is the data value of the
> register.
> 
> For a write command there is no RDATA, and buf should be assumed to
> be const and unmodifable. The original caller should not expect its data
> buffer to be corrupted by an sdw_nwrite().
> 
> Signed-off-by: Richard Fitzgerald <rf at opensource.cirrus.com>

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>

> ---
>  drivers/soundwire/cadence_master.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/soundwire/cadence_master.c b/drivers/soundwire/cadence_master.c
> index be9cd47f31ec..3ef472049980 100644
> --- a/drivers/soundwire/cadence_master.c
> +++ b/drivers/soundwire/cadence_master.c
> @@ -544,9 +544,12 @@ cdns_fill_msg_resp(struct sdw_cdns *cdns,
>  		return SDW_CMD_IGNORED;
>  	}
>  
> -	/* fill response */
> -	for (i = 0; i < count; i++)
> -		msg->buf[i + offset] = FIELD_GET(CDNS_MCP_RESP_RDATA, cdns->response_buf[i]);
> +	if (msg->flags == SDW_MSG_FLAG_READ) {
> +		/* fill response */
> +		for (i = 0; i < count; i++)
> +			msg->buf[i + offset] = FIELD_GET(CDNS_MCP_RESP_RDATA,
> +							 cdns->response_buf[i]);
> +	}
>  
>  	return SDW_CMD_OK;
>  }