[alsa-devel] [PATCH] ASoC: si476x: Remove custom register I/O implementation

[Andrey Smirnov]

On Thu, Sep 26, 2013 at 1:58 PM, Mark Brown <broonie at kernel.org> wrote:
> On Thu, Sep 26, 2013 at 12:58:27PM -0700, Andrey Smirnov wrote:
>> On Thu, Sep 26, 2013 at 12:43 PM, Mark Brown <broonie at kernel.org> wrote:
>
>> > What exactly is the locking you're talking about here?
>
>> I am talking about locking specific for si476x MFD device that is
>> hadled by si476x_core_lock / si476x_core_unlock. The code before the
>> patch has both externally exposed functions via V4L2 driver and SoC
>> driver obtain said lock for the duration of their interaction with the
>> device. The patch appears to remove lock acquisition for SoC
>> functions.
>
> But what exactly are these locks supposed to be protecting?
>
>> > The way the code is written it looks like the lock is being held to
>> > ensure there's no race due to a power state change.
>
>> That lock is being held to prevent device access contention between
>> all of the code that can be triggered to be executed via V4L2 ioctl
>> API and SoC API. As an example, I can open the radio device and start
>> tuning it using corresponding ioctl, meanwhile, parallel to that
>> process my other code is trying to change the sample rate of the
>> codec. To prevent those two from clashes both of them try to acquire
>> "core lock" with si476x_core_lock before the start doing anything with
>> chip/MFD.
>
> In what way might these things conflict?  What are the clashes you are
> concerned about?

That lock serves the purpose of making sure that
si476x_core_send_command, calls to which all the rest of the functions
boil down to, is not executed in parallel to itself. So I am concerned
that with the lock acquisition removal it would be possible to make
that condition happen.