linux-kernel - Re: [PATCH v2 3/6] powerpc: Convert flush_icache

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Message-ID: <20190903130430.GC31406@gate.crashing.org>
Date:   Tue, 3 Sep 2019 08:04:31 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     "Alastair D'Silva" <alastair@....ibm.com>
Cc:     alastair@...ilva.org, David Hildenbrand <david@...hat.com>,
        linux-kernel@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Qian Cai <cai@....pw>, Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Allison Randal <allison@...utok.net>
Subject: Re: [PATCH v2 3/6] powerpc: Convert flush_icache_range & friends to C

Hi!

On Tue, Sep 03, 2019 at 03:23:57PM +1000, Alastair D'Silva wrote:
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c

> +#if !defined(CONFIG_PPC_8xx) & !defined(CONFIG_PPC64)

Please write that as &&?  That is more usual, and thus, easier to read.

> +static void flush_dcache_icache_phys(unsigned long physaddr)

> +	asm volatile(
> +		"   mtctr %2;"
> +		"   mtmsr %3;"
> +		"   isync;"
> +		"0: dcbst   0, %0;"
> +		"   addi    %0, %0, %4;"
> +		"   bdnz    0b;"
> +		"   sync;"
> +		"   mtctr %2;"
> +		"1: icbi    0, %1;"
> +		"   addi    %1, %1, %4;"
> +		"   bdnz    1b;"
> +		"   sync;"
> +		"   mtmsr %5;"
> +		"   isync;"
> +		: "+r" (loop1), "+r" (loop2)
> +		: "r" (nb), "r" (msr), "i" (bytes), "r" (msr0)
> +		: "ctr", "memory");

This outputs as one huge assembler statement, all on one line.  That's
going to be fun to read or debug.

loop1 and/or loop2 can be assigned the same register as msr0 or nb.  They
need to be made earlyclobbers.  (msr is fine, all of its reads are before
any writes to loop1 or loop2; and bytes is fine, it's not a register).


Segher