linux-kernel - Re: [PATCH 3/6] irqchip: irq-mvebu-gicp: new driver for Marvell GICP

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Message-ID: <20170530165454.6ca24dbc@free-electrons.com>
Date:   Tue, 30 May 2017 16:54:54 +0200
From:   Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Ian Campbell <ijc+devicetree@...lion.org.uk>,
        Pawel Moll <pawel.moll@....com>,
        Mark Rutland <mark.rutland@....com>,
        Kumar Gala <galak@...eaurora.org>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        linux-arm-kernel@...ts.infradead.org,
        Nadav Haklai <nadavh@...vell.com>,
        Hanna Hawa <hannah@...vell.com>,
        Yehuda Yitschak <yehuday@...vell.com>,
        Antoine Tenart <antoine.tenart@...e-electrons.com>
Subject: Re: [PATCH 3/6] irqchip: irq-mvebu-gicp: new driver for Marvell
 GICP

Hello,

On Tue, 30 May 2017 14:55:57 +0100, Marc Zyngier wrote:

> > +	for (i = 0; i < GICP_INT_COUNT; i++)
> > +		writel(i, regs + GICP_CLRSPI_NSR_OFFSET);  
> 
> What does this do on an edge interrupt?

I guess nothing. What the ICU does is:

 * For level interrupts: when the interrupt wire is asserted, write to
   SETNSR, when the interrupt wire is deasserted, write to CLRNSR

 * For edge interrupts: only the interrupt assertion causes a write to
   SETNSR.

> I bet this doesn't have any effect

Indeed. But do we care? Can an edge interrupt be left pending from the
firmware?

>, so you may want to use the irq_set_irqchip_state() API to clear a
> potential pending state instead (and you may want to wire it in the
> ICU driver itself as well).

I'm not sure how to use this irq_set_irqchip_state() API. I guess it
needs a virq that corresponds to the GIC SPI interrupt, and I'm not
sure how to get that.

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com