Re: [PATCH 1/2] drivers: qcom: rpmh-rsc: simplify TCS locking

[Lina Iyer]

On Fri, Jul 19 2019 at 12:20 -0600, Stephen Boyd wrote:
> Quoting Lina Iyer (2019-07-01 08:29:06)
> > From: "Raju P.L.S.S.S.N" <rplsssn@xxxxxxxxxxxxxx>
> >
> > tcs->lock was introduced to serialize access with in TCS group. But
> > even without tcs->lock, drv->lock is serving the same purpose. So
> > use a single drv->lock.
>
> Isn't the downside now that we're going to be serializing access to the
> different TCSes when two are being written in parallel or waited on? I
> thought that was the whole point of splitting the lock into a TCS lock
> and a general "driver" lock that protects the global driver state vs.
> the specific TCS state.
Yes but we were holding the drv->lock as well as tcs->lock for the most
critical of the path anyways (writing to TCS). The added complexity
doesn't seem to help reduce the latency that it expected to reduce.
> > Other optimizations include -
> >  - Remove locking around clear_bit() in IRQ handler. clear_bit() is
> >    atomic.
> >  - Remove redundant read of TCS registers.
> >  - Use spin_lock instead of _irq variants as the locks are not held
> >    in interrupt context.
>
> Can you please split this patch up into 3 or 4 different patches? I'm
> not sure why any of these patches are marked with Fixes either. It's an
> optimization patch, not a fix patch, unless the optimization is really
> large somehow?
Okay. I will try that.
> > Fixes: 658628 ("drivers: qcom: rpmh-rsc: add RPMH controller for QCOM
> > SoCs")
> > Signed-off-by: Raju P.L.S.S.S.N <rplsssn@xxxxxxxxxxxxxx>
> > Signed-off-by: Lina Iyer <ilina@xxxxxxxxxxxxxx>
> > ---
> >  drivers/soc/qcom/rpmh-internal.h |  2 --
> >  drivers/soc/qcom/rpmh-rsc.c      | 37 +++++++++++---------------------
> >  drivers/soc/qcom/rpmh.c          | 20 +++++++----------
> >  3 files changed, 21 insertions(+), 38 deletions(-)
> >
> > diff --git a/drivers/soc/qcom/rpmh-internal.h b/drivers/soc/qcom/rpmh-internal.h
> > index a7bbbb67991c..969d5030860e 100644
> > --- a/drivers/soc/qcom/rpmh-internal.h
> > +++ b/drivers/soc/qcom/rpmh-internal.h
> > diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> > index e278fc11fe5c..92461311aef3 100644
> > --- a/drivers/soc/qcom/rpmh-rsc.c
> > +++ b/drivers/soc/qcom/rpmh-rsc.c
> > @@ -93,8 +93,7 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,
> >
> >  static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
> >  {
> > -       return !test_bit(tcs_id, drv->tcs_in_use) &&
> > -              read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id, 0);
> > +       return !test_bit(tcs_id, drv->tcs_in_use);
>
> This can be a diffedjusted rent patch. Why is reading the tcs register
> redundant? Please put that information in the commit text.
The tcs_in_use, is adjusted along with the DRV_STS and reading the
tcs_in_use should be enough.

Thanks for your review Stephen.

--Lina