Re: [PATCH] iio: mxs-lradc: Remove useless check in read_raw

[Marek Vasut <marex@denx.de>]

Dear Otavio Salvador,

> On Tue, Jul 2, 2013 at 2:36 PM, Marek Vasut <marex@denx.de> wrote:
> > Dear Otavio Salvador,
> > 
> >> On Tue, Jul 2, 2013 at 1:13 PM, Marek Vasut <marex@denx.de> wrote:
> >> > Dear Alexandre Belloni,
> >> > 
> >> >> On 02/07/2013 14:03, Marek Vasut wrote:
> >> >> > Dear Alexandre Belloni,
> >> >> > 
> >> >> >> Dear Marek,
> >> >> >> 
> >> >> >> I don't seem to be hitting that issue. I'm using 3.10rc7. Do you
> >> >> >> know how to reproduce it ?
> >> >> > 
> >> >> > The check is just redundant, it's not a bug.
> >> >> 
> >> >> Ok, that's what I understood first but then got confused by reports
> >> >> of it solving a bug.
> >> > 
> >> > It cannot solve a thing. If it does, then we have a problem.
> >> > 
> >> > What kind of bug do you see ? How can I replicate it ? Can you send me
> >> > a testcase?
> >> 
> >> As I said this code sometimes work. If you put a printf before this
> >> call it sometimes work. So I think we have a race somewhere.
> >> 
> >> When I were debugging this I found that when it works we have 10
> >> active channels, it seems.
> > 
> > Uh, the read_raw() should exit with -EBUSY, since the mutex_tryload()
> > will fail iff buffered operation is in progress. Or what do you mean by
> > having "10 active channels"?
> 
> The read_raw returned invalid. The onehot always returns false and I
> have 10 as mask comparing return.

Looking at the code.

the bitmap_set() will set (1 << chan->channel) into "mask" var.

The iio_validate_scan_mask_onehot is implemented like this:

688 bool iio_validate_scan_mask_onehot(struct iio_dev *indio_dev,
689         const unsigned long *mask)
690 {
691         return bitmap_weight(mask, indio_dev->masklength) == 1;
692 }

So if mask _always_ has exactly one bit set, the iio_validate_scan_mask_onehot 
will always return 1. Aaaand ... now I see why it fixes a bug for you.

if (ret)
 return -EINVAL;

This stuff above will always be if (1) so will always return -EINVAL. Dang!

Best regards,
Marek Vasut