Looking for API to possibly implement "mastered image transfer" for xf86-video-savage

[Alex Villací­s Lasso]

Michel Dänzer escribió:
> On Mon, 2008-11-10 at 13:37 -0500, Alex Villací­s Lasso wrote:
>   
>> The question is: is there any xserver support that might enable a driver 
>> to get pixmap data into either kind of situation? Either get the pixmap 
>> into physically contiguous pages and obtain the physical address of the 
>> start of data, or pre-copy the pixmap data into AGP memory (allocated by 
>> the driver on startup, if necessary)
>>     
>
> There isn't any such support in the X server; it would be mostly a
> kernel level thing anyway.
>
>   
>> so that the driver does not need to copy it into AGP memory every
>> single time.
>>     
>
> FWIW, that's what the radeon driver does currently.
>
>
>   
I could do that in savage too (copy into AGP and set up a mastered image 
transfer), but I have seen the radeon code, and it seems that the copy 
from system memory to AGP is done using a standard memcpy. Probably I am 
missing a clue, but I fail to understand how a memcpy from system memory 
to AGP, followed by an accelerated blit from AGP to framebuffer, can be 
any faster that a direct memcpy from system memory into the framebuffer. 
Particularly when (in the case of XVideo for savage) the copy must be 
done every single time for every frame.

I was reading 
http://dri.freedesktop.org/wiki/AGP?highlight=(CategoryFaq) , and the 
start of the document describes the "DMA model" of AGP usage, which 
closely matches what I think I need. Only that instead of allocating an 
AGP buffer and using it for all memory transfers, it would be useful to 
make the GART (temporarily) point into a buffer in userspace while 
preserving its contents. Even one page might be useful to make a faster 
transfer. But I might be wrong.

-- 
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