Re: Accessing AGP

[<uni...@sh...>]

Hi!

Vladimir Dergachev wrote:

>>>
>> This has just been implemented in the Unichrome driver, and I'm not 
>> sure wether it's the best or most appopriate way to do it but it 
>> works as follows:
>>
>> 1. The Mesa driver fills a "malloced" system memory buffer with 
>> vertex data.
>> 2. The Mesa driver then calls the DRM through a via-specific IOCTL. 
>> (via_ioctl.c)
>> 3. The via drm copies the buffer to another buffer in kernel system 
>> memory ( static storage ), (via_dma.c)
>> 4. The via drm verifies the content of the buffer to reject buffers 
>> that contain commands that are considered harmful. (via_verifier.c)
>> 5. The buffer is copied to AGP space, and the engine pointers are 
>> updated. (via_dma.c)
>>
>> The reason for 3. is that running the verifier directly on AGP memory 
>> is very slow.
>
>
> Hi Thomas,
>
>      Thank you very much for the explanation :)
>
>      What kind of verification of vertex data does unichrome need ?
>
>                      thank you !
>
>                          Vladimir Dergachev
>
On the Unichrome it's possible to do quite a lot using AGP DMA. Some of 
the things that can be done are not disclosed by VIA, but apparently you 
can blit memory contents from more or less anywhere to more or less 
anywhere....

What the command verifier does is that it lets commands thrugh that is 
knows:

1. Only accesses the 2D-engine or Mpeg engine through writes. (Other 
areas are blocked).
2. Does not attempt to fetch memory contents from system memory.
3. Does not attempt to fetch memory contents from AGP memory that is 
outside the user-mappable range (textures).

Frame-buffer memory is considered open territory, as is the 
user-mappable part of AGP-memory. Note that the AGP command buffers must 
NOT reside in the user-mappable parts of AGP-memory.

Regards
/Thomas



 



>>
>> /Thomas
>>
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