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From:   Vivek Gautam <vivek.gautam@codeaurora.org>
Date:   Wed, 19 Jun 2019 17:04:39 +0530
Message-ID: <CAFp+6iEwN6jeEGNxKVU5_i5NxdEbuF2ZggegEJZ1Rq6F=H34jg@mail.gmail.com>
Subject: Re: [PATCH v3 1/4] firmware: qcom_scm-64: Add atomic version of qcom_scm_call
To:     Will Deacon <will.deacon@arm.com>
Cc:     "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "robh+dt" <robh+dt@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        David Brown <david.brown@linaro.org>,
        "list@263.net:IOMMU DRIVERS <iommu@lists.linux-foundation.org>, Joerg
        Roedel <joro@8bytes.org>," <iommu@lists.linux-foundation.org>,
        Andy Gross <agross@kernel.org>,
        Robin Murphy <robin.murphy@arm.com>
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On Tue, Jun 18, 2019 at 11:25 PM Will Deacon <will.deacon@arm.com> wrote:
>
> On Wed, Jun 12, 2019 at 12:45:51PM +0530, Vivek Gautam wrote:
> > There are scnenarios where drivers are required to make a
> > scm call in atomic context, such as in one of the qcom's
> > arm-smmu-500 errata [1].
> >
> > [1] ("https://source.codeaurora.org/quic/la/kernel/msm-4.9/commit/
> >       drivers/iommu/arm-smmu.c?h=CogSystems-msm-49/
> >       msm-4.9&id=da765c6c75266b38191b38ef086274943f353ea7")
> >
> > Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
> > Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> > ---
> >  drivers/firmware/qcom_scm-64.c | 136 ++++++++++++++++++++++++++++-------------
> >  1 file changed, 92 insertions(+), 44 deletions(-)
> >
> > diff --git a/drivers/firmware/qcom_scm-64.c b/drivers/firmware/qcom_scm-64.c
> > index 91d5ad7cf58b..b6dca32c5ac4 100644
> > --- a/drivers/firmware/qcom_scm-64.c
> > +++ b/drivers/firmware/qcom_scm-64.c

[snip]

> > +
> > +static void qcom_scm_call_do(const struct qcom_scm_desc *desc,
> > +                          struct arm_smccc_res *res, u32 fn_id,
> > +                          u64 x5, bool atomic)
> > +{
>
> Maybe pass in the call type (ARM_SMCCC_FAST_CALL vs ARM_SMCCC_STD_CALL)
> instead of "bool atomic"? Would certainly make the callsites easier to
> understand.

Sure, will do that.

>
> > +     int retry_count = 0;
> > +
> > +     if (!atomic) {
> > +             do {
> > +                     mutex_lock(&qcom_scm_lock);
> > +
> > +                     __qcom_scm_call_do(desc, res, fn_id, x5,
> > +                                        ARM_SMCCC_STD_CALL);
> > +
> > +                     mutex_unlock(&qcom_scm_lock);
> > +
> > +                     if (res->a0 == QCOM_SCM_V2_EBUSY) {
> > +                             if (retry_count++ > QCOM_SCM_EBUSY_MAX_RETRY)
> > +                                     break;
> > +                             msleep(QCOM_SCM_EBUSY_WAIT_MS);
> > +                     }
> > +             }  while (res->a0 == QCOM_SCM_V2_EBUSY);
> > +     } else {
> > +             __qcom_scm_call_do(desc, res, fn_id, x5, ARM_SMCCC_FAST_CALL);
> > +     }
>
> Is it safe to make concurrent FAST calls?

I better add a spinlock here.

Thanks & regards
Vivek

>
> Will
> _______________________________________________
> iommu mailing list
> iommu@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu


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