lkml.org 
[lkml]   [2017]   [Oct]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 07/11] powerpc: make dma_cache_sync a no-op
From
Date


Le 03/10/2017 à 13:43, Christoph Hellwig a écrit :
> On Tue, Oct 03, 2017 at 01:24:57PM +0200, Christophe LEROY wrote:
>>> powerpc does not implement DMA_ATTR_NON_CONSISTENT allocations, so it
>>> doesn't make any sense to do any work in dma_cache_sync given that it
>>> must be a no-op when dma_alloc_attrs returns coherent memory.
>> What about arch/powerpc/mm/dma-noncoherent.c ?
>>
>> Powerpc 8xx doesn't have coherent memory.
>
> It doesn't implement the DMA_ATTR_NON_CONSISTENT interface either,
> so if it really doesn't have a way to provide dma coherent allocation
> (although the code in __dma_alloc_coherent suggests it does provide
> dma coherent allocations) I have no idea how it could ever have
> worked.
>

Yes indeed it provides coherent memory by allocation non cached memory.

And drivers aiming at using non coherent memory do it by using kmalloc()
with GFP_DMA then dma_map_single().
Then they use dma_sync_single_for_xxx(), which calls __dma_sync() on the
8xx and is a nop on other powerpcs.

Christophe

\
 
 \ /
  Last update: 2017-10-04 10:30    [W:0.082 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site