Re: [PATCH v4 3/3] iio: accel: bmc150: use guard(mutex) for mutex handling

[Jonathan Cameron]

On Tue, 18 Aug 2026 18:47:56 +0300
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> wrote:

> On Tue, Aug 18, 2026 at 04:41:35PM +0100, Gabriel Rondon wrote:
> > On Mon, Aug 17, 2026 at 06:39:18PM +0300, Andy Shevchenko wrote:  
> > > Not directly related to this change, but even in the original code what is
> > > protected here by the mutex? data->scan.channels?  
> > 
> > Agreed it is out of scope for this cleanup, so I left the scope unchanged.
> > 
> > Honest answer: not much that is obvious. data->scan.channels does not need
> > it, since the triggered handler is the only writer and the core serializes
> > it. The accel one-shot read is already gated with -EBUSY while buffering, so
> > bmc150_accel_get_axis cannot race the handler. What is left sharing
> > data->mutex and still reachable during capture is the temperature read, the
> > bandwidth get/set and scale set, and the event config. But since the handler
> > is a single regmap_bulk_read and regmap already serializes the bus, it is not
> > clear the driver mutex guards a real invariant here, and it may well be
> > vestigial.  
> 
> > Dropping it is a behavioral change worth its own patch and testing rather
> > than something to fold into a lock-syntax cleanup.  
> 
> Of course! Just made an observation.
> 
> > Happy to look into that separately.  
> 
> If you have HW to test, I would like to see such a change.
> 
See my reply to Yash's thread.  The lock scope may well expand as a trade
off against bloat of the iio_priv() structure.  If following what I suggest
it will be protecting the set of cachelines containing the various buffers
used for bulk reads during both DMA and whatever else is done with them.

Jonathan