Re: [PATCH 2/4] hwmon: (tps53679) Fix device ID comparison and printing in tps53676_identify()

[Guenter Roeck <linux@roeck-us.net>]

Hi,

On 3/29/26 10:09, Pradhan, Sanman wrote:
> From: Sanman Pradhan <psanman@juniper.net>
> 
> tps53676_identify() uses strncmp() to compare the device ID buffer
> against a byte sequence containing embedded non-printable bytes
> (\x53\x67\x60). strncmp() is semantically wrong for binary data
> comparison; use memcmp() instead.
> 
> Additionally, the buffer from i2c_smbus_read_block_data() is not
> NUL-terminated, so printing it with "%s" in the error path is
> undefined behavior and may read past the buffer. Use "%*ph" to
> hex-dump the actual bytes returned.
> 
> Also add a short-read guard: if fewer than 5 bytes are returned,
> report -EIO (protocol/hardware failure) rather than -ENODEV, since
> a truncated response is not the same as a wrong device ID.
> 
Ah, but we don't know and can not assume that this is a truncated ID.
It might as well be some other device.

> Fixes: cb3d37b59012 ("hwmon: (pmbus/tps53679) Add support for TI TPS53676")
> Signed-off-by: Sanman Pradhan <psanman@juniper.net>
> ---
>   drivers/hwmon/pmbus/tps53679.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/tps53679.c b/drivers/hwmon/pmbus/tps53679.c
> index 1a6abc32afe2..d6600502d6b0 100644
> --- a/drivers/hwmon/pmbus/tps53679.c
> +++ b/drivers/hwmon/pmbus/tps53679.c
> @@ -175,8 +175,12 @@ static int tps53676_identify(struct i2c_client *client,
>   	ret = i2c_smbus_read_block_data(client, PMBUS_IC_DEVICE_ID, buf);
>   	if (ret < 0)
>   		return ret;
> -	if (strncmp("TI\x53\x67\x60", buf, 5)) {
> -		dev_err(&client->dev, "Unexpected device ID: %s\n", buf);
> +	if (ret < 5) {
> +		dev_err(&client->dev, "Short device ID read: %*ph\n", ret, buf);
> +		return -EIO;

This is not an -EIO: It suggests a different device. Please change the comparison
to "ret != 0" and return -ENODEV. In other words,

> +	}
> +	if (memcmp(buf, "TI\x53\x67\x60", 5)) {

Just change the original code. The expected device ID, according to the datasheet,
is, in hex, "54 49 53 67 60 00", with a terminating 0x00. So, when using memcmp,
the comparison should be something like

	if (ret != 6 || memcmp(buf, "TI\x53\x67\x60\x00", 6)) {

Thanks,
Guenter