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

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Message-ID: <CAGETcx8Yw2QDYBYNpqVt_kPHnokFR+qinr5GAJ1byVWMuc3PLQ@mail.gmail.com>
Date:   Wed, 21 Jul 2021 14:07:49 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     John Stultz <john.stultz@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Andy Gross <agross@...nel.org>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        Maulik Shah <mkshah@...eaurora.org>,
        Todd Kjos <tkjos@...gle.com>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "list@....net:IOMMU DRIVERS <iommu@...ts.linux-foundation.org>, Joerg
        Roedel <joro@...tes.org>," <iommu@...ts.linux-foundation.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable
 as a permenent module

On Wed, Jul 21, 2021 at 1:23 PM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Wed 21 Jul 13:00 CDT 2021, Saravana Kannan wrote:
>
> > On Wed, Jul 21, 2021 at 10:24 AM John Stultz <john.stultz@...aro.org> wrote:
> > >
> > > On Wed, Jul 21, 2021 at 4:54 AM Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > On Wed, Jul 07, 2021 at 04:53:20AM +0000, John Stultz wrote:
> > > > > Allow the qcom_scm driver to be loadable as a permenent module.
> > > >
> > > > This feels like a regression, it should be allowed to be a module.
> > >
> > > I'm sorry, I'm not sure I'm following you, Greg.  This patch is trying
> > > to enable the driver to be able to be loaded as a module.
> >
> > I think the mix up might be that Greg mentally read "permanent module"
> > as "builtin"?
> >
> > "permanent module" is just something that can't be unloaded once it's
> > loaded. It's not "builtin".
> >
>
> Afaict there's nothing in this patch that makes it more or less
> permanent.

The lack of a module_exit() makes it a permanent module. If you do
lsmod, it'll mark this as "[permanent]".

-Saravana

> The module will be quite permanent (in practice) because
> several other core modules reference symbols in the qcom_scm module.
>
> But thanks to a previous patch, the qcom_scm device comes with
> suppress_bind_attrs, to prevent that the device goes away from a simple
> unbind operation - which the API and client drivers aren't designed to
> handle.
>
> So, it would have been better in this case to omit the word "permanent"
> from the commit message, but the change is good and I don't want to
> rebase my tree to drop that word.
>
> Thanks,
> Bjorn
>
> > -Saravana
> >
> > >
> > > > > This still uses the "depends on QCOM_SCM || !QCOM_SCM" bit to
> > > > > ensure that drivers that call into the qcom_scm driver are
> > > > > also built as modules. While not ideal in some cases its the
> > > > > only safe way I can find to avoid build errors without having
> > > > > those drivers select QCOM_SCM and have to force it on (as
> > > > > QCOM_SCM=n can be valid for those drivers).
> > > > >
> > > > > Reviving this now that Saravana's fw_devlink defaults to on,
> > > > > which should avoid loading troubles seen before.
> > > >
> > > > fw_devlink was supposed to resolve these issues and _allow_ code to be
> > > > built as modules and not forced to be built into the kernel.
> > >
> > > Right. I'm re-submitting this patch to enable a driver to work as a
> > > module, because earlier attempts to submit it ran into boot trouble
> > > because fw_devlink wasn't yet enabled.
> > >
> > > I worry something in my description made it seem otherwise, so let me
> > > know how you read it and I'll try to avoid such confusion in the
> > > future.
> > >
> > > thanks
> > > -john