linux-kernel - Re: [PATCH 1/2] MIPS: Add basic support for Loongson1B (UPDATED)

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Date:	Sun, 25 Sep 2011 07:40:18 -0600
From:	Shane McDonald <mcdonald.shane@...il.com>
To:	wu zhangjin <wuzhangjin@...il.com>
Cc:	keguang.zhang@...il.com, linux-mips@...ux-mips.org,
	linux-kernel@...r.kernel.org, ralf@...ux-mips.org,
	r0bertz@...too.org, chenj@...ote.com
Subject: Re: [PATCH 1/2] MIPS: Add basic support for Loongson1B (UPDATED)

>> diff --git a/arch/mips/include/asm/mach-loongson1/regs-clk.h b/arch/mips/include/asm/mach-loongson1/regs-clk.h
>> new file mode 100644
>> index 0000000..7a09d6a
>> --- /dev/null
>> +++ b/arch/mips/include/asm/mach-loongson1/regs-clk.h
>> @@ -0,0 +1,32 @@
>> +/*
>> + * Copyright (c) 2011 Zhang, Keguang <keguang.zhang@...il.com>
>> + *
>> + * Loongson1 Clock Register Definitions.
>> + *
>> + * This program is free software; you can redistribute  it and/or modify it
>> + * under  the terms of  the GNU General  Public License as published by the
>> + * Free Software Foundation;  either version 2 of the  License, or (at your
>> + * option) any later version.
>> + */
>> +
>> +#ifndef __ASM_MACH_LOONGSON1_REGS_CLK_H
>> +#define __ASM_MACH_LOONGSON1_REGS_CLK_H
>> +
>> +#define LS1_CLK_REG(x)         ((void __iomem *)(LOONGSON1_CLK_BASE + (x)))
>
> "volatile" keyword may be required for __iomem access, the same to the
> following similar usage.
>
> Considering a scene is(LS1_XXX_REG(X) doesn't really exist):
>
> LS1_XXX_REG(X) = 0;              /* put cpu into idle and wait interrupt */
> LS1_XXX_REG(X) = 7;              /* recover the cpu frequency to the highest */
>
> If no "volatile" keyword indicated, the above two lines will be
> intelligently but wrongly removed by compiler.

No -- please see Documentation/volatile-considered-harmful.txt,
particularly the paragraph starting at line 49.  This macro
is only being used as an argument to __raw_readl,
as it should be.

Shane
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