Re: [PATCH v2 3/5] irqchip: Allow QCOM_PDC to be loadable as a permanent module

From: Marc Zyngier <maz@kernel.org>
To: Stephen Boyd <swboyd@chromium.org>
Cc: John Stultz <john.stultz@linaro.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>,
	Maulik Shah <mkshah@codeaurora.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: [PATCH v2 3/5] irqchip: Allow QCOM_PDC to be loadable as a permanent module
Date: Sun, 12 Jul 2020 10:27:20 +0100	[thread overview]
Message-ID: <87r1thxevb.wl-maz@kernel.org> (raw)
In-Reply-To: <159442366514.1987609.434612639050774557@swboyd.mtv.corp.google.com>

On Sat, 11 Jul 2020 00:27:45 +0100,
Stephen Boyd <swboyd@chromium.org> wrote:
> 
> Quoting John Stultz (2020-07-10 15:44:18)
> > On Thu, Jul 9, 2020 at 11:02 PM Stephen Boyd <swboyd@chromium.org> wrote:
> > >
> > > Does it work? I haven't looked in detail but I worry that the child
> > > irqdomain (i.e. pinctrl-msm) would need to delay probing until this
> > > parent irqdomain is registered. Or has the hierarchical irqdomain code
> > > been updated to handle the parent child relationship and wait for things
> > > to probe or be loaded?
> > 
> > So I can't say I know the underlying hardware particularly well, but
> > I've been using this successfully on the Dragonboard 845c with both
> > static builds as well as module enabled builds.
> > And the same patch has been in the android-mainline and android-5.4
> > kernels for a while without objections from QCOM.
> > 
> > As to the probe ordering question, Saravana can maybe speak in more
> > detail if it's involved in this case but the fw_devlink code has
> > addressed many of these sorts of ordering issues.
> > However, I'm not sure if I'm lucking into the right probe order, as we
> > have been able to boot android-mainline w/ both fw_devlink=on and
> > fw_devlink=off (though in the =off case, we need
> > deferred_probe_timeout=30 to give us a bit more time for modules to
> > load after init starts).
> > 
> 
> Ok I looked at the code (sorry for not checking earlier) and I see this in
> msm_gpio_init()
> 
>         np = of_parse_phandle(pctrl->dev->of_node, "wakeup-parent", 0);
>         if (np) {
>                 chip->irq.parent_domain = irq_find_matching_host(np,
>                                                  DOMAIN_BUS_WAKEUP);
>                 of_node_put(np);
>                 if (!chip->irq.parent_domain)
>                         return -EPROBE_DEFER;
> 
> so it looks like we'll probe defer the pinctrl driver until the pdc module
> loads. Meaning it should work to have pinctrl builtin and pdc as a module.

What I hope is that eventually fw_devlink will become the norm (on by
default), and that probe deferral will become a thing of the past.

	M.

-- 
Without deviation from the norm, progress is not possible.