Re: [PATCH v2] iio: stm32-dac: Replace indio_dev->mlock with own device lock

Jonathan Cameron
2020-08-29T15:46:31Z

On Thu, 27 Aug 2020 13:00:36 +0300
Alexandru Ardelean <ardeleanalex@gmail.com> wrote:

> On Thu, Aug 27, 2020 at 12:03 PM Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
> >
> > On 8/27/20 10:55 AM, Alexandru Ardelean wrote:
> > > On Wed, Aug 26, 2020 at 3:03 PM Alexandru Ardelean
> > > <alexandru.ardelean@analog.com> wrote:
> > >> From: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> > >>
> > >> As part of the general cleanup of indio_dev->mlock, this change replaces
> > >> it with a local lock. The lock protects against potential races when
> > >> reading the CR reg and then updating, so that the state of pm_runtime
> > >> is consistent between the two operations.
> > >>
> > >> Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
> > >> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> > >> ---
> > > Forgot the changelog here.
> > > Apologies.
> > >
> > > Changelog v1 -> v2:
> > > * removed whitespace change for 'common' field
> > > * updated comment about the lock usage
> >
> > Hi Alexandru,
> >
> > Sorry if I missed it... is there an update on the comment :-) ?
>
> For a moment there, I thought I didn't.
> GMail's threading is confusing.
>
> ----------------------------------------------------------------------------
> As part of the general cleanup of indio_dev->mlock, this change replaces
> it with a local lock. The lock protects against potential races when
> reading the CR reg and then updating, so that the state of pm_runtime
> is consistent between the two operations.
> ----------------------------------------------------------------------------
I think this got confused...

see below.

>
> >
> > Best Regards,
> > Fabrice
> > >
> > >> drivers/iio/dac/stm32-dac.c | 12 ++++++++----
> > >> 1 file changed, 8 insertions(+), 4 deletions(-)
> > >>
> > >> diff --git a/drivers/iio/dac/stm32-dac.c b/drivers/iio/dac/stm32-dac.c
> > >> index 092c796fa3d9..7a8aed476850 100644
> > >> --- a/drivers/iio/dac/stm32-dac.c
> > >> +++ b/drivers/iio/dac/stm32-dac.c
> > >> @@ -26,9 +26,11 @@
> > >> /**
> > >> * struct stm32_dac - private data of DAC driver
> > >> * @common: reference to DAC common data
> > >> + * @lock: lock to protect the data buffer during regmap ops

The original comment was:

In this particular case I'm not sure that's what mlock was being used for.
I think it's about avoiding races around checking if powered down and
actually doing it.

And Fabrice's reply:

Hi Sergiu,

Indeed, purpose is to protect against a race here when reading CR, and
updating it via regmap (this also makes the subsequent pm_runtime calls
to be balanced based on this).
(Side note: there is no data buffer involved for the DAC.)
Could you please update the comment ?

Thanks,
Fabrice

> > >> */
> > >> struct stm32_dac {
> > >> struct stm32_dac_common *common;
> > >> + struct mutex lock;
> > >> };