Re: [PATCH 3/16] Kconfig update for lemote fulong mini-PC

[Fuxin Zhang <fxzhang@ict.ac.cn>]

Uhler, Mike wrote:
>> Yes. Most 64bit MIPS processors cannot access 64bit content 
>> of registers when it is in 32bit mode.
>>     
>
> For clarity, there is no 32/64-bit mode in MIPS processors.  There is a
> mode in which 64-bit OPERATIONS are enabled (that is, those instructions
> which operate on the full width of the registers) - See the definition
> of 64-bit Operations Enable in the MIPS64 Architecture for Programmers,
> volume III.  Note that such operations are always enabled while the
> processor is running in Kernel Mode.
>
> The patch is a little short on context, but if you've got a 64-bit
> kernel, I had always assumed that save/restore of context is always done
> with LD/SD, not by figuring out whether a process has 64-bit operations
> enabled, then doing a conditional LD/SD or LW/SW.
>
>   
This patch for 32bit kernel. We want to save/restore 64bit register 
content because the high 32bit of register might be used by multimedia 
programs for loongson processor, such as mplayer.

> /gmu
> ---
> Michael Uhler, Chief Technology Officer
> MIPS Technologies, Inc.   Email: uhler AT mips.com
> 1225 Charleston Road      Voice:  (650)567-5025   FAX:   (650)567-5225
> Mountain View, CA 94043
>    
>
>   
>> -----Original Message-----
>> From: linux-mips-bounce@linux-mips.org 
>> [mailto:linux-mips-bounce@linux-mips.org] On Behalf Of Fuxin Zhang
>> Sent: Wednesday, April 18, 2007 6:32 AM
>> To: Ralf Baechle
>> Cc: tiansm@lemote.com; linux-mips@linux-mips.org; Fuxin Zhang
>> Subject: Re: [PATCH 3/16] Kconfig update for lemote fulong mini-PC
>>
>>
>>     
>>>> +
>>>>     
>>>>         
>>> Is there anything in implementation of this option 
>>>       
>> Loongson2-specific?
>>     
>>>   
>>>       
>> Yes. Most 64bit MIPS processors cannot access 64bit content 
>> of registers when it is in 32bit mode.
>>
>> Loongson2 has no 32/64 mode bit in fact.
>>
>> And the usage arise from Loongson2's multimedia extension, 
>> which is also uniq.
>>     
>>> If not then I suggest we make this option loook like:
>>>
>>>    bool "Save 64bit integer registers" if 
>>>       
>> CPU_SUPPORTS_64BIT_KERNEL && 
>>     
>>> 32BIT
>>>
>>> Somebody else might have a use for it!
>>>
>>>   Ralf
>>>
>>>
>>>
>>>
>>>   
>>>       
>>     
>
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