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

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Date:   Fri, 19 Jul 2019 11:20:22 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Lina Iyer <ilina@...eaurora.org>, andy.gross@...aro.org,
        bjorn.andersson@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        rnayak@...eaurora.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, dianders@...omium.org,
        mkshah@...eaurora.org, "Raju P.L.S.S.S.N" <rplsssn@...eaurora.org>,
        Lina Iyer <ilina@...eaurora.org>
Subject: Re: [PATCH 1/2] drivers: qcom: rpmh-rsc: simplify TCS locking

Quoting Lina Iyer (2019-07-01 08:29:06)
> From: "Raju P.L.S.S.S.N" <rplsssn@...eaurora.org>
> 
> 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.

> 
> 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?

> 
> Fixes: 658628 ("drivers: qcom: rpmh-rsc: add RPMH controller for QCOM
> SoCs")
> Signed-off-by: Raju P.L.S.S.S.N <rplsssn@...eaurora.org>
> Signed-off-by: Lina Iyer <ilina@...eaurora.org>
> ---
>  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 different patch. Why is reading the tcs register
redundant? Please put that information in the commit text.