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From:	David Daney <ddaney@caviumnetworks.com>
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To:	post@pfrst.de, Ralf Baechle <ralf@linux-mips.org>
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Subject: Re: cacheflush system call-MIPS
References: <f5a7b3810902100716t2658ce95t2dcc7f85634522@mail.gmail.com> <20090211131649.GA1365@linux-mips.org> <Pine.LNX.4.58.0902140002180.408@Indigo2.Peter> <20090213235603.GA32274@linux-mips.org> <Pine.LNX.4.58.0902150312460.459@Indigo2.Peter>
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peter fuerst wrote:
>> Why does it need that flush?
> 
> To prepare the update-area (in the Shadow-FB) for DMA to RE.
> 
> 

And on systems where the root frame buffer is directly manipulated by 
the CPU, the video system is continually using DMA to refresh the 
display.  A cache flush can be required to eliminate transient visual 
glitches.

David Daney



> kind regards
> 
> 
> 
> On Fri, 13 Feb 2009, Ralf Baechle wrote:
> 
>> Date: Fri, 13 Feb 2009 23:56:03 +0000
>> From: Ralf Baechle <ralf@linux-mips.org>
>> To: peter fuerst <post@pfrst.de>
>> Cc: naresh kamboju <naresh.kernel@gmail.com>, linux-mips@linux-mips.org
>> Subject: Re: cacheflush system call-MIPS
>>
>> On Sat, Feb 14, 2009 at 12:50:46AM +0100, peter fuerst wrote:
>>
>>> there is one more good reason to ... : the Impact Xserver needs to do
>>> a cacheflush(a,w,DCACHE) as part of the refresh-sequence.
>>> And hence requires a sys_cacheflush, let's say, more conforming to the
>>> man-page (or some disgusting new ioctl in the Impact kernel-driver to
>>> do an equivalent operation ;-)
>> Why does it need that flush?
>>
>>   Ralf
>>
>>
> 
>