Re: [PATCH 1/3] iio: core: Add devm_ APIs for iio_channel_{get,release}

[Laxman Dewangan]

On Sunday 10 April 2016 07:35 PM, Jonathan Cameron wrote:
> On 06/04/16 15:58, Laxman Dewangan wrote:
> > Hi Daniel,
> >
> >
> > On Wednesday 06 April 2016 07:19 PM, Daniel Baluta wrote:
> > > On Wed, Apr 6, 2016 at 1:31 PM, Laxman Dewangan <ldewangan@xxxxxxxxxx> wrote:
> > > > Some of kernel driver uses the IIO framework to get the sensor
> > > > value via ADC or IIO HW driver. The client driver get iio channel
> > > > by iio_channel_get() and release it by calling iio_channel_release().
> > > >
> > > > Add resource managed version (devm_*) of these APIs so that if client
> > > > calls the devm_iio_channel_get() then it need not to release it explicitly,
> > > > it can be done by managed device framework when driver get un-binded.
> > > >
> > > > This reduces the code in error path and also need of .remove callback in
> > > > some cases.
> > > Please provide at least one example of code that uses this API.
> > Most of client for this APIs are in other subsystem.
> > When I was working on the patch
> > [PATCH 2/2] thermal: generic-adc: Add ADC based thermal sensor driver
> >
> > if I have devm_iio_channel_get() then I can get .remove callback at all.
> >
> > I did not use this new APIs in my patch because they are in different subsystem.
> It's actually worse than that having taken a quick look at the generic-adc thermal patch
> you reference above.
> (perhaps worth cc'ing linux-iio for next version of that).
Sure. I will CC.

> Without this devm function set you have a race in remove in which I think you can
> get attempts to access the channels after they have been released...
Yaah, possibly race for very small time possible.

The limitation of devm_ api usage is that, we can keep using this till 
we have devm_ api continuous and if some resource are not there for 
devm_ then we can not use further.
Possibly, I need to wait for the devm_iio_channel_get() to merge and 
available for all subsystem to use (next release) and then only I can 
use devm_thermal_zone_of_sensor_register().