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Message-ID: <4CB8A5A0.9060801@caviumnetworks.com>
Date:   Fri, 15 Oct 2010 12:04:00 -0700
From:   David Daney <ddaney@caviumnetworks.com>
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To:     "Gleb O. Raiko" <raiko@niisi.msk.ru>, linux-mips@linux-mips.org
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Subject: Re: [PATCH] MIPS: Implement __read_mostly
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On 10/15/2010 04:25 AM, Gleb O. Raiko wrote:
> On 14.10.2010 23:36, David Daney wrote:
>> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
>> --- a/arch/mips/kernel/setup.c
>> +++ b/arch/mips/kernel/setup.c
>> @@ -69,7 +69,7 @@ static char __initdata
>> builtin_cmdline[COMMAND_LINE_SIZE] = CONFIG_CMDLINE;
>> * mips_io_port_base is the begin of the address space to which x86 style
>> * I/O ports are mapped.
>> */
>> -const unsigned long mips_io_port_base __read_mostly = -1;
>> +const unsigned long mips_io_port_base = -1;
>> EXPORT_SYMBOL(mips_io_port_base);
>
> While we're here could we eliminate mips_io_port_base for boards that
> don't need it.
>

That is a logically separate issue, so would be the subject of a 
different patch.  I don't personally plan on working on it, but would be 
happy to review anything someone else came up with.

David Daney


> Now, it almost might be done by defining something like
> __swizzle_addr_[bwlq](port) ((port) - mips_io_port_base)
>
> Unfortunately, __swizzle_addr_[bwlq] is also used for memory acceeses
> too (in read/write[bwlq]), so definition above doesn't work.
>
> By providing two variants, e.g. __swizzle_io_addr_[bwlq] and
> __swizzle_mem_addr_[bwlq] we can eliminate unnecessary loads of
> mips_io_port_base.
>
> BTW, in recent kernels the trick with mips_io_port_base doesn't work
> well anyway. The solely purpose of the trick was to prevent loading of
> mips_io_port_base across function calls. Now drivers tend to use
> ioread/iowrite that don't use mips_io_port_base at all or use its own
> wrappers for in/out[bwlq] that _do_ load mips_io_port_base on every call.
>
> Gleb.
>