[lkml]   [2009]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH][RFC] asm-generic:remove calling flush_write_buffers() in dma_sync_*_for_cpu
On Sun, Jun 28, 2009 at 03:34:35PM +0000, Arnd Bergmann wrote:
> On Sunday 28 June 2009 14:39:19 wrote:
> > From: Ming Lei <>
> >
> > dma_sync_*_for_cpu() is introduced to make cpu access dma buffers safely when
> > dma transfer is over, it seems there is nothing to do with cpu write buffer,
> > so remove it.
> >
> > Signed-off-by: Ming Lei <>
> Right, this looks correct. On a related note, flush_write_buffers is
> architecture specific right now: only x86 and frv implement it at all,
> though and with slightly different semantics.

This doen't look correct to me. The sync functions may do bounce buffering
which is all about copying data from one place in main memory to another. So we
need these flush_write_buffer() calls in the _for_cpu path too.

> Maybe it would be more consistent to change the dma_map_* and
> dma_sync_*_for_device stuff there to wmb() to make it portable
> to other architectures.

If we change it to wmb() it would be executed every time there even if the
processor doesn't require it. Other architectures could simply add a
flush_write_buffers() implemention if they want to adapt the common dma-mapping
implementation, no?


| Advanced Micro Devices GmbH
Operating | Karl-Hammerschmidt-Str. 34, 85609 Dornach bei München
System |
Research | Geschäftsführer: Thomas M. McCoy, Giuliano Meroni
Center | Sitz: Dornach, Gemeinde Aschheim, Landkreis München
| Registergericht München, HRB Nr. 43632

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2009-06-29 14:35    [W:0.066 / U:2.148 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site