Re: New dma-noncoherent code, looking for comment and people to test

I agree. Is someone already working on that or should I do it ?

Remi


On Mon, 2008-09-29 at 13:03 -0500, Kumar Gala wrote:

On Sep 29, 2008, at 12:26 PM, Remi Machet wrote:

quoted

Hi,

I rewrote dma-noncoherent.c and I am looking for people to review  
and test it
on various platforms that use it to make sure I did not introduce  
any bug.
The platforms affected by this change are those that define
CONFIG_NOT_COHERENT_CACHE:
ppc44x
walnut
makalu
kilauea
ep405
adder875
ep88xc
taishan
warp
sam440ep
sequoia
bamboo
canyonlands
rainier
katmai
ebony
mpc885_ads
mpc866_ads
ppc40x
c2k (already tested)
prpmc2800

The old code in dma-noncoherent.c uses a memory pool at a hard coded
virtual address set by CONFIG_CONSISTENT_START (typically  
0xFF100000). If not
set carefully this address can conflict with early ioremap in systems
that enable HIGHMEM, on top of that the code is overly complex  
because it
needs to have its own memory manager.
This is why I tried to re-implement the code using standard memory
management APIs. The new code does not require the user to set
CONFIG_CONSISTENT_START or CONFIG_CONSISTENT_SIZE, is much smaller and
simplier. It also can allocate as much memory as available in ZONE_DMA
(instead of being limited by CONFIG_CONSISTENT_SIZE).

I also removed the HIGHMEM support in dma_sync since memory  
allocated for
DMA transfer should always be in ZONE_DMA (ie not in ZONE_HIGHMEM).

Looking forward to any comment about why this code may not work or  
is not
as good as the original. If you do test this code on your platform,  
let me
know how it goes ... if no-one object and no bug is found I will  
submit
this patch in a month or so.

Thanks !

Remi

We really should change this code over to the new dma changes Becky's  
introduced so we just have a non-coherent set of DMA ops (thus we can  
do both non-coherent and coherent in the same system).

- k

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