On Sun, Sep 25, 2011 at 9:40 PM, Shane McDonald
<mcdonald.shane@xxxxxxxxx> wrote:
>>> 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@xxxxxxxxx>
>>> + *
>>> + * 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 first line 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.
Yeah, __raw_readl/writel() will use volatile to prevent it from
optimization, thanks ;)
"within the kernel, I/O memory accesses are always done through
accessor functions;
accessing I/O memory directly through pointers is frowned upon and
does not work on all
architectures. Those accessors are written to prevent unwanted
optimization,
....
- The above-mentioned accessor functions might use volatile on
architectures where direct I/O memory access does work. Essentially,
each accessor call becomes a little critical section on its own and
ensures that the access happens as expected by the programmer.
...
Patches to remove volatile variables are generally welcome - as long as
they come with a justification which shows that the concurrency issues have
been properly thought through.
"
Thanks & Regards,
Wu Zhangjin
>
> Shane
>
