linux-kernel - Re: [PATCH v2 2/2] irqchip: Add Qualcomm MPM controller driver

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Message-ID: <20211201073622.GJ10105@dragon>
Date:   Wed, 1 Dec 2021 15:36:25 +0800
From:   Shawn Guo <shawn.guo@...aro.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Maulik Shah <quic_mkshah@...cinc.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Loic Poulain <loic.poulain@...aro.org>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] irqchip: Add Qualcomm MPM controller driver

On Tue, Nov 30, 2021 at 10:44:15AM +0000, Marc Zyngier wrote:
> On Tue, 30 Nov 2021 09:17:08 +0000,
> Shawn Guo <shawn.guo@...aro.org> wrote:
> > 
> > On Tue, Nov 30, 2021 at 08:42:53AM +0000, Marc Zyngier wrote:
> > > On Tue, 30 Nov 2021 02:31:52 +0000,
> > > Shawn Guo <shawn.guo@...aro.org> wrote:
> > > > 
> > > > + Maulik
> > > > 
> > > > On Mon, Nov 29, 2021 at 03:24:39PM +0000, Marc Zyngier wrote:
> > > > [...]
> > > > > > > > @@ -430,6 +430,14 @@ config QCOM_PDC
> > > > > > > >  	  Power Domain Controller driver to manage and configure wakeup
> > > > > > > >  	  IRQs for Qualcomm Technologies Inc (QTI) mobile chips.
> > > > > > > >  
> > > > > > > > +config QCOM_MPM
> > > > > > > > +	bool "QCOM MPM"
> > > > > > > 
> > > > > > > Can't be built as a module?
> > > > > > 
> > > > > > The driver is implemented as a builtin_platform_driver().
> > > > > 
> > > > > This, on its own, shouldn't preclude the driver from being built as a
> > > > > module. However, the config option only allows it to be built in. Why?
> > > > 
> > > > I just tried to build it as a module, and it seems that "irq_to_desc" is
> > > > only available for built-in build.
> > > 
> > > Yet another thing that you should not be using. The irqdomain code
> > > gives you everything you need without having to resort to the
> > > internals of the core IRQ infrastructure.
> > 
> > I see.  I should use irq_get_irq_data() rather than &desc->irq_data.
> 
> Even better:
> 
> 	desc = irq_resolve_mapping(domain, hwirq);
> 
> Job done. No extra tracking, no dubious hack in the unmask callback,
> works with modules.
> 
> > 
> > > 
> > > > > Furthermore, why would you look up anywhere other than the wake-up
> > > > > domain? My impression was that only these interrupts would require
> > > > > being re-triggered.
> > > > 
> > > > Both domains have MPM pins that could wake up system.
> > > 
> > > Then why do you need two domains?
> > 
> > This is basically the same situation as qcom-pdc, and I have some
> > description about that in the commit log:
> > 
> > - For given SoC, a fixed number of MPM pins are supported, e.g. 96 pins
> >   on QCM2290.  Each of these MPM pins can be either a MPM_GIC pin or
> >   a MPM_GPIO pin. The mapping between MPM_GIC pin and GIC interrupt
> >   is defined by SoC, as well as the mapping between MPM_GPIO pin and
> >   GPIO number.  The former mapping can be found as the SoC data in this
> >   MPM driver, while the latter can be found as the msm_gpio_wakeirq_map[]
> >   in TLMM driver.
> > 
> > - Two irq domains are created for a single irq_chip to handle MPM_GIC
> >   and MPM_GPIO pins respectively, i.e. MPM_GIC domain and MPM_GPIO domain.
> >   The former is a child domain of GIC irq domain, while the latter is
> >   a parent domain of TLMM/GPIO irq domain.
> 
> That doesn't answer my question.
> 
> It doesn't matter what the pins are used for as long as you can
> identify which ones are routed to the GIC and which are not. You are
> obviously are able to do so, since you are able to disconnect part of
> the hierarchy (why is qcom_mpm_gic_alloc() named as such, since most
> of the interrupts it deals with are *never* routed to the GIC).
> 
> All the interrupts have the same irqchip callbacks and act on the same
> 'priv' data, so they it is obvious they don't overlap in the hwirq
> space.
> 
> Ergo: you can implement the whole thing with a single domain. All you
> need to make sure is that you identify the pins that are routed to the
> GIC, and you already have that information.

You are right!  A single domain works.  Nice and clean!  Thanks for the
comment, Marc!

Shawn