linux-kernel - Re: [PATCH] iio: accel: cros_ec_accel_legacy: Mark expected switch fall-throughs

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Date:   Wed, 15 Aug 2018 12:50:10 -0500
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Marcus Folkesson <marcus.folkesson@...il.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: accel: cros_ec_accel_legacy: Mark expected switch
 fall-throughs

Hi Marcus,

On 8/15/18 12:27 PM, Marcus Folkesson wrote:
> Hi,
> 
> On Wed, Aug 15, 2018 at 11:38:52AM -0500, Gustavo A. R. Silva wrote:
>> In preparation to enabling -Wimplicit-fallthrough, mark switch cases
>> where we are expecting to fall through.
>>
>> Addresses-Coverity-ID: 1462408 ("Missing break in switch")
>> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
>> ---
>>  drivers/iio/accel/cros_ec_accel_legacy.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/iio/accel/cros_ec_accel_legacy.c b/drivers/iio/accel/cros_ec_accel_legacy.c
>> index 063e89e..d609654 100644
>> --- a/drivers/iio/accel/cros_ec_accel_legacy.c
>> +++ b/drivers/iio/accel/cros_ec_accel_legacy.c
>> @@ -385,8 +385,10 @@ static int cros_ec_accel_legacy_probe(struct platform_device *pdev)
>>  		switch (i) {
>>  		case X:
>>  			ec_accel_channels[X].scan_index = Y;
>> +			/* fall through */
>>  		case Y:
>>  			ec_accel_channels[Y].scan_index = X;
>> +			/* fall through */
>>  		case Z:
>>  			ec_accel_channels[Z].scan_index = Z;
>>  		}
> 
> Hum, I'm not sure we are supposed to fall through here, even if it does
> not hurt to do so.

Yeah. You're right. It doesn't hurt but is actually redundant. I think
the original intention was to break instead of falling through.

> I even think we can remove the switch and put that outside the for-loop,
> e.g:
> 
> 	ec_accel_channels[X].scan_index = Y;
> 	ec_accel_channels[Y].scan_index = X;
> 	ec_accel_channels[Z].scan_index = Z;
> 
> 	for (i = X ; i < MAX_AXIS; i++) {
> 		if (state->sensor_num == MOTIONSENSE_LOC_LID && i != Y)
> 			state->sign[i] = -1;
> 		else
> 			state->sign[i] = 1;
> 	}
> 

I like this, but the code clearly depends on MAX_AXIS. So, if MAX_AXIS
will be always 3, then the change you suggest is just fine. Otherwise,
it seems that adding a break to each case is the right way to go.

What do you think?

Thanks for the feedback.
--
Gustavo