linux-kernel - Re: [EXT] Re: [PATCH v9 2/4] irqchip: Add IMX MU MSI controller driver

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Date:   Sat, 10 Sep 2022 15:40:29 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Frank Li <frank.li@....com>
Cc:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kw@...ux.com" <kw@...ux.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Peng Fan <peng.fan@....com>,
        Aisheng Dong <aisheng.dong@....com>,
        "jdmason@...zu.us" <jdmason@...zu.us>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "kishon@...com" <kishon@...com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "ntb@...ts.linux.dev" <ntb@...ts.linux.dev>,
        "lznuaa@...il.com" <lznuaa@...il.com>,
        "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
        "manivannan.sadhasivam@...aro.org" <manivannan.sadhasivam@...aro.org>
Subject: Re: [EXT] Re: [PATCH v9 2/4] irqchip: Add IMX MU MSI controller driver

On Fri, 09 Sep 2022 15:52:45 +0100,
Frank Li <frank.li@....com> wrote:
> 
> > > +     select IRQ_DOMAIN
> > > +     select IRQ_DOMAIN_HIERARCHY
> > > +     select GENERIC_MSI_IRQ_DOMAIN
> > > +     help
> > > +       MU work as MSI controller to do general doorbell
> > 
> > I'm not sure this is that generic. It really is limited to CPU-to-CPU
> > interrupts.
> 
> [Frank Li] I think the only limitation is only 4 irq numbers. 
> The principle CPU to CPU irq is the same as MSI.

Not quite. Normal MSIs are device-to-CPU. CPU-to-CPU are normally
IPIs, and this one falls in the middle.

> What's  your preferred help description?

<quote>
	Provide a driver for the MU block used as a CPU-to-CPU MSI
	controller. This requires a specially crafted DT to make use
	of this driver.

	If unsure, say N.
</quote>

	M.

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