On 1/5/25 11:25 AM, Jonathan Cameron wrote:
> From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
>
> Initial thought was to do something similar to __cond_lock()
>
> do_iio_device_claim_direct_mode(iio_dev) ? : ({ __acquire(iio_dev); 0; })
> + Appropriate static inline iio_device_release_direct_mode()
>
> However with that, sparse generates false positives. E.g.
>
> drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c:1811:17: warning: context imbalance in 'st_lsm6dsx_read_raw' - unexpected unlock
Even if false positives aren't technically wrong, if sparse is having a hard
time reasoning about the code, then it is probably harder for humans to reason
about the code as well. So rewriting these false positives anyway could be
justified beyond just making the static analyzer happy.
>
> So instead, this patch rethinks the return type and makes it more
> 'conditional lock like' (which is part of what is going on under the hood
> anyway) and return a boolean - true for successfully acquired, false for
> did not acquire.
I think changing this function to return bool instead of int is nice change
anyway since it makes writing the code less prone authors to trying to do
something "clever" with the ret variable. And it also saves one one line of
code.
>
> To allow a migration path given the rework is now no trivial, take a leaf
> out of the naming of the conditional guard we currently have for IIO
> device direct mode and drop the _mode postfix from the new functions giving
> iio_device_claim_direct() and iio_device_release_direct()
>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> include/linux/iio/iio.h | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index 56161e02f002..4ef2f9893421 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -662,6 +662,28 @@ int iio_push_event(struct iio_dev *indio_dev, u64 ev_code, s64 timestamp);
> int iio_device_claim_direct_mode(struct iio_dev *indio_dev);
> void iio_device_release_direct_mode(struct iio_dev *indio_dev);
>
> +/*
> + * Helper functions that allow claim and release of direct mode
> + * in a fashion that doesn't generate false positives from sparse.
> + */
> +static inline bool iio_device_claim_direct(struct iio_dev *indio_dev) __cond_acquires(indio_dev)
Doesn't __cond_acquires depend on this patch [1] that doesn't look like it was
ever picked up in sparse?
[1]: https://lore.kernel.org/all/CAHk-=wjZfO9hGqJ2_hGQG3U_XzSh9_XaXze=HgPdvJbgrvASfA@xxxxxxxxxxxxxx/
> +{
> + int ret = iio_device_claim_direct_mode(indio_dev);
> +
> + if (ret)
> + return false;
> +
> + __acquire(iio_dev);
> +
> + return true;
> +}
> +
> +static inline void iio_device_release_direct(struct iio_dev *indio_dev) __releases(indio_dev)
> +{
> + iio_device_release_direct_mode(indio_dev);
> + __release(indio_dev);
> +}
> +
> /*
> * This autocleanup logic is normally used via
> * iio_device_claim_direct_scoped().
In summary, assuming we get the required changed merged into sparse, I think this
seems like the best solution.
