Re: [PATCH] iio:adc:ti-adc084s021: Endian casting tidy ups.

["Ardelean, Alexandru" <alexandru.Ardelean@analog.com>]

On Sat, 2019-11-09 at 12:11 +0000, Jonathan Cameron wrote:
> [External]
> 
> On Mon, 4 Nov 2019 15:08:12 +0000
> "Ardelean, Alexandru" <alexandru.Ardelean@analog.com> wrote:
> 
> > On Sun, 2019-10-13 at 10:47 +0100, jic23@kernel.org wrote:
> > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > 
> > > Highlighted by sparse:
> > > CHECK   drivers/iio/adc/ti-adc084s021.c
> > > drivers/iio/adc/ti-adc084s021.c:79:26: warning: incorrect type in
> > > assignment (different base types)
> > > drivers/iio/adc/ti-adc084s021.c:79:26:    expected unsigned short
> > > [unsigned] [short] [usertype] <noident>
> > > drivers/iio/adc/ti-adc084s021.c:79:26:    got restricted __be16
> > > <noident>
> > > drivers/iio/adc/ti-adc084s021.c:110:24: warning: cast to restricted
> > > __be16
> > > drivers/iio/adc/ti-adc084s021.c:110:24: warning: cast to restricted
> > > __be16
> > > drivers/iio/adc/ti-adc084s021.c:110:24: warning: cast to restricted
> > > __be16
> > > drivers/iio/adc/ti-adc084s021.c:110:24: warning: cast to restricted
> > > __be16
> > >   
> Thanks for looking at this. I'd missed entirely that a void *
> was hiding some more nastiness!
> 
> > This one looks a bit tricky.
> > And looks like it could use a bit more cleanup than this.
> > Otherwise sparse may come along and complain about more stuff.
> > 
> > One thing that would be good, would be to change:
> > 
> > int adc084s021_adc_conversion(struct adc084s021 *adc, void *data)
> > 
> > to
> > 
> > int adc084s021_adc_conversion(struct adc084s021 *adc, __be16 *data, int
> > buf_size)   [1]
> > 
> > 
> > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > Cc: Mårten Lindahl <martenli@axis.com>
> > > ---
> > >  drivers/iio/adc/ti-adc084s021.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/iio/adc/ti-adc084s021.c b/drivers/iio/adc/ti-
> > > adc084s021.c
> > > index bdedf456ee05..42966f2eb3d8 100644
> > > --- a/drivers/iio/adc/ti-adc084s021.c
> > > +++ b/drivers/iio/adc/ti-adc084s021.c
> > > @@ -68,7 +68,7 @@ static int adc084s021_adc_conversion(struct
> > > adc084s021
> > > *adc, void *data)
> > >  {
> > >  	int n_words = (adc->spi_trans.len >> 1) - 1; /* Discard first word
> > > */
> > >  	int ret, i = 0;
> > > -	u16 *p = data;
> > > +	__be16 *p = data;
> > >  
> > >  	/* Do the transfer */
> > >  	ret = spi_sync(adc->spi, &adc->message);
> > > @@ -87,6 +87,7 @@ static int adc084s021_read_raw(struct iio_dev
> > > *indio_dev,
> > >  {
> > >  	struct adc084s021 *adc = iio_priv(indio_dev);
> > >  	int ret;
> > > +	__be16 value;
> > >  
> > >  	switch (mask) {
> > >  	case IIO_CHAN_INFO_RAW:
> > > @@ -101,13 +102,13 @@ static int adc084s021_read_raw(struct iio_dev
> > > *indio_dev,
> > >  		}
> > >  
> > >  		adc->tx_buf[0] = channel->channel << 3;
> > > -		ret = adc084s021_adc_conversion(adc, val);
> > > +		ret = adc084s021_adc_conversion(adc, &value);  
> > 
> > Following [1], this could be called
> > with  "adc084s021_adc_conversion(adc,
> > &value, 1)" to make sure it's not doing any stack corruption. I can't
> > tell
> > if this is doing any or not; the code is a bit fuzzy to me.
> 
> I'm fairly sure current code is safe as IIO_CHAN_INFO_RAW reads occur
> with protection against buffered mode and when not in buffered mode the
> magic length is 4 which is divided by 2 and has 1 subtracted giving a
> safe value of 1.  This dance is ensure there is only one place where
> the length is recorded and avoid recomputing it in
> *_buffer_trigger_handler.
> We could stash it in the private data though for easier to read code.

No idea what's best here.
I am mostly interested in getting the sparse checks up-n-running, so that
we don't have another dance with Greg [as the ones with the ADIS patches].

> 
> Agreed that the type change to __be16 * definitely makes sense though.
> Will respin with that.
> 
> > The neat part is that memcpy() could be used to then access the data on
> > rx_buf.
> 
> We could do that, but as it's not part of the fix really I'd rather leave
> that for another day.  Not sure anything stops us doing this whilst doing
> this tidy up even without passing in the size.

Let's leave things here as-is for now.
sparse checks [or any new checks we're adding] feel more important right
now.

Thanks
Alex

> 
> Thanks,
> 
> Jonathan
> 
> > 
> > >  		iio_device_release_direct_mode(indio_dev);
> > >  		regulator_disable(adc->reg);
> > >  		if (ret < 0)
> > >  			return ret;
> > >  
> > > -		*val = be16_to_cpu(*val);
> > > +		*val = be16_to_cpu(value);
> > >  		*val = (*val >> channel->scan_type.shift) & 0xff;
> > >  
> > >  		return IIO_VAL_INT;