linux-kernel - Re: [PATCH 7/9] irqchip: add a RISC-V PLIC driver

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Date:   Tue, 31 Jul 2018 18:37:41 +0200
From:   Christoph Hellwig <hch@....de>
To:     Atish Patra <atish.patra@....com>
Cc:     Christoph Hellwig <hch@....de>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "jason@...edaemon.net" <jason@...edaemon.net>,
        "marc.zyngier@....com" <marc.zyngier@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "anup@...infault.org" <anup@...infault.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "shorne@...il.com" <shorne@...il.com>
Subject: Re: [PATCH 7/9] irqchip: add a RISC-V PLIC driver

On Fri, Jul 27, 2018 at 05:04:52PM -0700, Atish Patra wrote:
>> +#define MAX_DEVICES			1024
>> +#define MAX_CONTEXTS			15872
>> +
>
> Is there any way we can preserve some of the comments in the original patch 
> about memory-mapped control registers or at least a reference where to find 
> the register offset calculations?

The comments really do not help to describe a why or how.  I'd love to
add a reference to a spec, but I could not find anything that looks
like an authoritative spec for the SiFive PLIC layout.

>> +	u32 __iomem *reg = plic_regs + ENABLE_BASE + ctxid * ENABLE_PER_HART;
>
> shouldn't it be
> u32 __iomem *reg = plic_regs + ENABLE_BASE + ctxid * ENABLE_PER_HART + 
> (hwirq / 32) * 4;

Yes, it should.  Fixed.

>> +		if (unlikely(irq <= 0)) {
>> +			pr_warn_ratelimited("can't find mapping for hwirq %lu\n",
>> +					hwirq);
>
> Ratlimiting the warning message here didn't help as ack_bad_irq() still 
> print message still flooded the console without any useful info.

I've dropped the somewhat pointless ack_bad_irq call, thanks.