linux-kernel - Re: [RFC][PATCH 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable as a permenent module

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Message-ID: <20200703122343.GB18652@willie-the-truck>
Date:   Fri, 3 Jul 2020 13:23:44 +0100
From:   Will Deacon <will@...nel.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Marc Zyngier <maz@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Linus Walleij <linus.walleij@...aro.org>,
        Lina Iyer <ilina@...eaurora.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Todd Kjos <tkjos@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, linux-gpio@...r.kernel.org
Subject: Re: [RFC][PATCH 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be
 loadable as a permenent module

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@...nel.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?

Will