linux-kernel - Re: [PATCH v2 5/5] arm64: irqchip/gic-v3: Select priorities at boot time

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Date: Fri, 21 Jun 2024 08:48:32 +0100
From: Marc Zyngier <maz@...nel.org>
To: "Liao, Chang" <liaochang1@...wei.com>
Cc: Mark Rutland <mark.rutland@....com>,
	<linux-arm-kernel@...ts.infradead.org>,
	<alexandru.elisei@....com>,
	<catalin.marinas@....com>,
	<linux-kernel@...r.kernel.org>,
	<tglx@...utronix.de>,
	<will@...nel.org>
Subject: Re: [PATCH v2 5/5] arm64: irqchip/gic-v3: Select priorities at boot time

On Fri, 21 Jun 2024 07:23:54 +0100,
"Liao, Chang" <liaochang1@...wei.com> wrote:
> 
> 
> 
> 在 2024/6/17 19:18, Mark Rutland 写道:
> >  	cpus_have_group0 = gic_has_group0();
> 
> > +#define __gicv3_prio_to_ns(p)	(0xff & ((p) << 1))
> > +#define __gicv3_ns_to_prio(ns)	(0x80 | ((ns) >> 1))
> 
> What about refactoring the gic_has_group0() using the mapping macros
> between PMR priority and GIC priority like this:
> 
> ---------------%<-----------------
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -882,6 +882,7 @@ static bool gic_has_group0(void)
>  {
>         u32 val;
>         u32 old_pmr;
> +       u32 prio = BIT(8 - gic_get_pribits());
> 
>         old_pmr = gic_read_pmr();
> 
> @@ -896,12 +897,12 @@ static bool gic_has_group0(void)
>          * becomes 0x80. Reading it back returns 0, indicating that
>          * we're don't have access to Group0.
>          */
> -       gic_write_pmr(BIT(8 - gic_get_pribits()));
> +       gic_write_pmr(prio);
>         val = gic_read_pmr();
> 
>         gic_write_pmr(old_pmr);
> 
> -       return val != 0;
> +       return val != (__gicv3_prio_to_ns(__gicv3_ns_to_prio(prio)));
>  }
> --------------->%-----------------

No, that's terrible, and makes it simply impossible to understand what
is happening without looking at 3 layers of indirection.

Read the comment, and realise that the code implements exactly that.

	M.

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