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Re: what is the purpose of the following LE->BE patch to arch/mips/inclu

To: "Robert P. J. Day" <rpjday@crashcourse.ca>
Subject: Re: what is the purpose of the following LE->BE patch to arch/mips/include/asm/io.h?
From: Matt Turner <mattst88@gmail.com>
Date: Fri, 20 Feb 2015 20:04:51 -0800
Cc: "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>
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On Fri, Feb 20, 2015 at 8:00 PM, Matt Turner <mattst88@gmail.com> wrote:
> On Fri, Feb 20, 2015 at 1:53 AM, Robert P. J. Day <rpjday@crashcourse.ca> 
> wrote:
>>
>>   was recently handed a MIPS-based dev board (can't name the vendor,
>> NDA) that *typically* runs in LE mode but, because of a proprietary
>> binary that must be run on the board and was compiled as BE, has to be
>> run in BE mode.
>>
>>   the vendor supplied a yoctoproject layer that seems to work fine
>> but, in changing the DEFAULTTUNE to big-endian, the following patch
>> had to be applied to the 3.14 kernel tree to the file
>> arch/mips/include/asm/io.h in order to get output from the console
>> port as the system was booting:
>>
>> 326c326,333
>> <               *__mem = __val;                                         \
>> ---
>>>       {                                                                     
>>>           \
>>>               if (sizeof(type) == sizeof(u32))                \
>>>               {                                                             
>>>           \
>>>                       *__mem = __cpu_to_le32(__val);  \
>
> They're byte swapping a value if they're in big endian mode.
>
>>>               }                                                             
>>>           \
>>>               else                                                          
>>>   \
>>>                       *__mem = __val;                                       
>>>   \
>
> And they don't seem to really understand the __cpu_to_le32 macro...

Sorry, I should be more precise. They're byte swapping 32-bit values
if they're in big endian mode, and copying everything else without
conversion.

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