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Date:   Fri, 3 Jul 2020 18:19:12 +0530
From:   Vinod Koul <vkoul@kernel.org>
To:     Will Deacon <will@kernel.org>, John Stultz <john.stultz@linaro.org>
Cc:     Marc Zyngier <maz@kernel.org>, lkml <linux-kernel@vger.kernel.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Linus Walleij <linus.walleij@linaro.org>,
        Lina Iyer <ilina@codeaurora.org>,
        Saravana Kannan <saravanak@google.com>,
        Todd Kjos <tkjos@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        iommu@lists.linux-foundation.org, linux-gpio@vger.kernel.org
Subject: Re: [RFC][PATCH 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be
 loadable as a permenent module
Message-ID: <20200703124912.GM273932@vkoul-mobl>
References: <20200616061338.109499-1-john.stultz@linaro.org>
 <20200616061338.109499-6-john.stultz@linaro.org>
 <0be86735238a0f8b0c25934e2ed39eee@kernel.org>
 <CALAqxLUZBdiLBRcp1GW9rGxt1KhgNVQ86MuPXZcXdx2wFLZk6w@mail.gmail.com>
 <20200703122343.GB18652@willie-the-truck>
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On 03-07-20, 13:23, Will Deacon wrote:
> On Tue, Jun 16, 2020 at 01:52:32PM -0700, John Stultz wrote:
> > On Tue, Jun 16, 2020 at 12:55 AM Marc Zyngier <maz@kernel.org> wrote:
> > > On 2020-06-16 07:13, John Stultz wrote:
> > > > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > > > index b510f67dfa49..714893535dd2 100644
> > > > --- a/drivers/iommu/Kconfig
> > > > +++ b/drivers/iommu/Kconfig
> > > > @@ -381,6 +381,7 @@ config SPAPR_TCE_IOMMU
> > > >  config ARM_SMMU
> > > >       tristate "ARM Ltd. System MMU (SMMU) Support"
> > > >       depends on (ARM64 || ARM || (COMPILE_TEST && !GENERIC_ATOMIC64)) &&
> > > > MMU
> > > > +     depends on QCOM_SCM || !QCOM_SCM #if QCOM_SCM=m this can't be =y
> > >
> > > This looks a bit ugly. Could you explain why we need this at the SMMU
> > > level? I'd have expected the dependency to flow the other way around...
> > 
> > Yea, so the arm-smmu-qcom.c file calls directly into the qcom-scm code
> > via qcom_scm_qsmmu500_wait_safe_toggle()
> >   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/iommu/arm-smmu-qcom.c?h=v5.8-rc1#n44
> > 
> > So if ARM_SMMU=y and QCOM_SCM=m we get:
> > drivers/iommu/arm-smmu-qcom.o: In function `qcom_smmu500_reset':
> > arm-smmu-qcom.c:(.text+0xb4): undefined reference to
> > `qcom_scm_qsmmu500_wait_safe_toggle'
> > 
> > Do you have a suggestion for an alternative approach?
> 
> Can you use symbol_get() or something like that? How are module dependencies
> handled by other drivers?

So drivers deal with this by making rules in Kconfig which will prohibit
this case. QCOM_SCM depends on ARM_SMMU with the caveat that if ARM_SMMU
is a module, QCOM_SCM cant be inbuilt.

This can be done by adding below line in Kconfig for QCOM_SCM:

        depends on ARM_SMMU || !ARM_SMMU

This is quite prevalent is drivers to ensure dependency like this

Thanks
-- 
~Vinod