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

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Date:   Tue, 3 Sep 2019 16:28:09 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Alastair D'Silva <alastair@....ibm.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, Nicholas Piggin <npiggin@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Paul Mackerras <paulus@...ba.org>, alastair@...ilva.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



Le 03/09/2019 à 15:04, Segher Boessenkool a écrit :
> 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.

Do you mean \n has to be added after the ; ?

> 
> 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).

Can you explicit please ? Doesn't '+r' means that they are input and 
output at the same time ?

"to be made earlyclobbers", what does this means exactly ? How to do that ?

Christophe