Re: [PATCH v2 2/2] iio: light: as73211: fix channel handling in only-color triggered buffer

[Jonathan Cameron <jic23@kernel.org>]

On Wed, 4 Dec 2024 17:20:47 +0100
Christian Eggers <ceggers@arri.de> wrote:

> On Wednesday, 4 December 2024, 00:55:32 CET, Javier Carrasco wrote:
> > The channel index is off by one unit if AS73211_SCAN_MASK_ALL is not
> > set (optimized path for color channel readings), and it must be shifted
> > instead of leaving an empty channel for the temperature when it is off.
> > 
> > Once the channel index is fixed, the uninitialized channel must be set
> > to zero to avoid pushing uninitialized data.
> > 
> > Cc: stable@vger.kernel.org
> > Fixes: 403e5586b52e ("iio: light: as73211: New driver")
> > Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
> > ---
> >  drivers/iio/light/as73211.c | 17 +++++++++++++----
> >  1 file changed, 13 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/iio/light/as73211.c b/drivers/iio/light/as73211.c
> > index be0068081ebb..2d45dfeda406 100644
> > --- a/drivers/iio/light/as73211.c
> > +++ b/drivers/iio/light/as73211.c
> > @@ -672,9 +672,12 @@ static irqreturn_t as73211_trigger_handler(int irq __always_unused, void *p)
> >  
> >  		/* AS73211 starts reading at address 2 */
> >  		ret = i2c_master_recv(data->client,
> > -				(char *)&scan.chan[1], 3 * sizeof(scan.chan[1]));
> > +				(char *)&scan.chan[0], 3 * sizeof(scan.chan[0]));
> >  		if (ret < 0)
> >  			goto done;
> > +
> > +		/* Avoid pushing uninitialized data */
> > +		scan.chan[3] = 0;
> >  	}
> >  
> >  	if (data_result) {
> > @@ -682,9 +685,15 @@ static irqreturn_t as73211_trigger_handler(int irq __always_unused, void *p)
> >  		 * Saturate all channels (in case of overflows). Temperature channel
> >  		 * is not affected by overflows.
> >  		 */
> > -		scan.chan[1] = cpu_to_le16(U16_MAX);
> > -		scan.chan[2] = cpu_to_le16(U16_MAX);
> > -		scan.chan[3] = cpu_to_le16(U16_MAX);
> > +		if (*indio_dev->active_scan_mask == AS73211_SCAN_MASK_ALL) {
> > +			scan.chan[1] = cpu_to_le16(U16_MAX);
> > +			scan.chan[2] = cpu_to_le16(U16_MAX);
> > +			scan.chan[3] = cpu_to_le16(U16_MAX);
> > +		} else {
> > +			scan.chan[0] = cpu_to_le16(U16_MAX);
> > +			scan.chan[1] = cpu_to_le16(U16_MAX);
> > +			scan.chan[2] = cpu_to_le16(U16_MAX);
> > +		}
> >  	}
> >  
> >  	iio_push_to_buffers_with_timestamp(indio_dev, &scan, iio_get_time_ns(indio_dev));
> > 
> >   
> 
> With this change, having only X, Y and Z in the scan_mask (without the
> temperature channel) works fine.
> 
> But it looks that there is still another problem if a single color channel
> (e.g. X) is omitted from the scan mask (which probably wouldn't make much
> sense in practice).  If I am right, the layout of scan.chan[] is also wrong for
> that case, so e.g. if omitting X, the application will get the X values where
> it expects the temperature value (which isn't read from the hardware at all).
> 
> Does it make sense to write a follow-up patch for this? I fear that taking all
> possible combinations into account could make the driver more complicated than
> necessary.  Or is there a good example how to handle such combinations?
> 
Good spot. I'd fallen for assuming a driver worked the way I thought it would
and not checked everything necessary was there.

Hmm. This is a bit odd. Driver seems to be written with assumption that the IIO
core is doing demux.  That doesn't work unless available_scan_masks is set.

Make that
{
	AS73211_SCAN_MASK_ALL,
	AS73211_SCAN_MASK_COLOR,
	0,
};

And then if you enable fewer channels, the IIO core will still enable one of the
sets in available_scan_masks and then do the relevant data manipulation to repack
as necessary.

I'll not pick this patch up as it makes sense to fix both issues together.

Thanks

Jonathan

> 
> Tested-by: Christian Eggers <ceggers@arri.de>
> 
> 
> 
>