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From: John Stultz <john.stultz@linaro.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Maulik Shah <mkshah@codeaurora.org>,
	Jason Cooper <jason@lakedaemon.net>,
	Saravana Kannan <saravanak@google.com>,
	Marc Zyngier <maz@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	lkml <linux-kernel@vger.kernel.org>,
	Lina Iyer <ilina@codeaurora.org>,
	"open list:GPIO SUBSYSTEM" <linux-gpio@vger.kernel.org>,
	iommu@lists.linux-foundation.org, Andy Gross <agross@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Todd Kjos <tkjos@google.com>
Subject: Re: [PATCH v2 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable as a permenent module
Date: Thu, 29 Oct 2020 18:02:14 -0700	[thread overview]
Message-ID: <CALAqxLW13=cvTX3ghskb9uG_YoVh7kvp8UQGUB8mVDGYXHWpVQ@mail.gmail.com> (raw)
In-Reply-To: <ae6ba27a-d3c8-8b98-c263-ec779ef35738@arm.com>

On Wed, Oct 28, 2020 at 7:51 AM Robin Murphy <robin.murphy@arm.com> wrote:
> Hmm, perhaps I'm missing something here, but even if the config options
> *do* line up, what prevents arm-smmu probing before qcom-scm and
> dereferencing NULL in qcom_scm_qsmmu500_wait_safe_toggle() before __scm
> is initialised?

Oh man, this spun me on a "wait, but how does it all work!" trip. :)

So in the non-module case, the qcom_scm driver is a subsys_initcall
and the arm-smmu is a module_platform_driver, so the ordering works
out.

In the module case, the arm-smmu code isn't loaded until the qcom_scm
driver finishes probing due to the symbol dependency handling.

To double check this, I added a big msleep at the top of the
qcom_scm_probe to try to open the race window you described, but the
arm_smmu_device_probe() doesn't run until after qcom_scm_probe
completes.

So at least as a built in / built in, or a module/module case its ok.
And in the case where arm-smmu is a module and qcom_scm is built in
that's ok too.

Its just the case my patch is trying to prevent is where arm-smmu is
built in, but qcom_scm is a module that it can't work (due to build
errors in missing symbols,  or if we tried to use function pointers to
plug in the qcom_scm - the lack of initialization ordering).

Hopefully that addresses your concern? Let me know if I'm still
missing something.

thanks
-john
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  reply	other threads:[~2020-10-30  1:02 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-25  0:10 [PATCH v2 0/5] Allow for qcom-pdc, pinctrl-msm and qcom-scm drivers to be loadable as modules John Stultz
2020-06-25  0:10 ` [PATCH v2 1/5] irq: irqdomain: Export irq_domain_update_bus_token John Stultz
2020-06-25  0:10 ` [PATCH v2 2/5] irq: irqchip: Export irq_chip_retrigger_hierarchy and irq_chip_set_vcpu_affinity_parent John Stultz
2020-06-25  0:10 ` [PATCH v2 3/5] irqchip: Allow QCOM_PDC to be loadable as a permanent module John Stultz
2020-06-26  7:42   ` Stephen Boyd
2020-06-27  1:34     ` John Stultz
2020-06-27  9:37       ` Marc Zyngier
2020-07-10  6:02         ` Stephen Boyd
2020-07-10 22:44           ` John Stultz
2020-07-10 23:27             ` Stephen Boyd
2020-07-12  9:27               ` Marc Zyngier
2020-06-25  0:10 ` [PATCH v2 4/5] pinctrl: qcom: Allow pinctrl-msm code to be loadable as a module John Stultz
2020-06-25  0:10 ` [PATCH v2 5/5] firmware: QCOM_SCM: Allow qcom_scm driver to be loadable as a permenent module John Stultz
2020-07-02 12:47   ` Greg Kroah-Hartman
2020-07-02 14:18   ` Will Deacon
2020-07-10  3:28     ` John Stultz
2020-07-10  7:54       ` Will Deacon
2020-07-10 22:21         ` John Stultz
2020-07-13 20:41           ` Will Deacon
2020-07-13 20:48             ` John Stultz
2020-07-14  7:56               ` Will Deacon
2020-10-28  5:53             ` John Stultz
2020-10-28 13:51               ` Will Deacon
2020-10-28 14:51                 ` Robin Murphy
2020-10-30  1:02                   ` John Stultz [this message]
2020-10-30 14:12                     ` Robin Murphy
2020-10-31  0:12                       ` John Stultz
2020-10-30  6:09                 ` John Stultz

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