lkml.org 
[lkml]   [2010]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: USB transfer_buffer allocations on 64bit systems
On Fri, 9 Apr 2010, Oliver Neukum wrote:

> Am Freitag, 9. April 2010 17:15:43 schrieb Alan Stern:
> > > > Then usb_submit_urb(urb[i]) will copy the appropriate four bytes to a
> > > > bounce buffer and map the bounce buffer. Accesses to the other parts
> > > > of xbuf won't violate the cacheline rules, because xbuf isn't mapped
> > > > for DMA -- only the bounce buffer is. When urb[i] completes, the
> > > > bounce buffer contents will be copied back to the original four bytes
> > > > in xbuf. Again, there is no violation of cacheline rules.
> > >
> > > I think you are assuming that either every or no part of the buffer is mapped
> > > for DMA in place. I don't think you can assume that.
> >
> > Yes I can, because the code that makes this decision is part of
> > usbcore and it is under m
>
> It seems to me that in usbcore you can positively know that a buffer
> will be mapped. However if the mapping is not done in usbcore you
> cannot know what the HCD driver will do to a buffer, in particular
> you don't know whether it will be processed by PIO or mapped for
> DMA.

The mapping is always done either by usb_buffer_alloc() or by
map_urb_for_dma(). Both functions are in usbcore.

> Maybe I understand this wrongly. Which code exactly were you refering to?

Search for usages of "syncbuf" and "sync_dma" in sound/usb/usbaudio.c.

Alan Stern



\
 
 \ /
  Last update: 2010-04-09 23:23    [W:0.136 / U:0.204 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site