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

From: Alexandru Ardelean <ardeleanalex@gmail.com>
To: Jonathan Cameron <jic23@kernel.org>
Cc: Fabrice Gasnier <fabrice.gasnier@st.com>,
	Alexandru Ardelean <alexandru.ardelean@analog.com>,
	linux-iio <linux-iio@vger.kernel.org>,
	linux-stm32@st-md-mailman.stormreply.com,
	LKML <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org, alexandre.torgue@st.com,
	Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Subject: Re: [PATCH v2] iio: stm32-dac: Replace indio_dev->mlock with own device lock
Date: Wed, 2 Sep 2020 09:12:22 +0300	[thread overview]
Message-ID: <CA+U=DsrMFasSO3ka-U_Dkn2BXF4qmfp4ejv=gjf4epo6WxFnUQ@mail.gmail.com> (raw)
In-Reply-To: <20200829164613.3be1b2b1@archlinux>

On Sat, Aug 29, 2020 at 6:46 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> 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

oh, silly me;
it's about this comment;
will re-spin

>
> 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;
> > > >>  };
>