linux-kernel - Re: [PATCH 2/2] powerpc: cleanup hw

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Date:   Tue, 27 Aug 2019 19:36:35 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Nicholas Piggin <npiggin@...il.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] powerpc: cleanup hw_irq.h



Le 27/08/2019 à 19:29, Segher Boessenkool a écrit :
> On Tue, Aug 27, 2019 at 10:48:24PM +1000, Nicholas Piggin wrote:
>> Christophe Leroy's on August 27, 2019 6:13 pm:
>>> +#define wrtee(val)	asm volatile("wrtee %0" : : "r" (val) : "memory")
>>> +#define wrteei(val)	asm volatile("wrteei %0" : : "i" (val) : "memory")
>>
>> Can you implement just one macro that uses __builtin_constant_p to
>> select between the imm and reg versions? I forgot if there's some
>> corner cases that prevent that working with inline asm i constraints.
> 
> static inline void wrtee(long val)
> {
> 	asm volatile("wrtee%I0 %0" : : "n"(val) : "memory");
> }

Great, didn't know that possibility.

Can it be used with any insn, for instance with add/addi ?
Or with mr/li ?

> 
> (This output modifier goes back to the dark ages, some 2.4 or something).

Hope Clang support it ...

Christophe

> 
> 
> Segher
>