lkml.org 
[lkml]   [2010]   [Apr]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: USB transfer_buffer allocations on 64bit systems
On Wed, Apr 07, 2010 at 03:13:11PM -0400, Alan Stern wrote:
> On Wed, 7 Apr 2010, Takashi Iwai wrote:
>
> > > Ok, I'll write some dummies for usb_malloc() and usb_zalloc() which
> > > will just call kmalloc() with GFP_DMA32 for now.
> >
> > Can't we provide only zalloc() variant? Zero'ing doesn't cost much,
> > and the buffer allocation shouldn't be called too often.
>
> Linus specifically requested us to avoid using kzalloc in usbfs. I
> can't find the message in the email archives, but Greg KH should be
> able to confirm it.
>
> As long as we're imitating kmalloc for one use, we might as well make
> it available to all.
>
> > > And while at it,
> > > usb_alloc_buffer() will be renamed to usb_alloc_consistent().
> >
> > Most of recent functions are named with "coherent".
>
> Yes, the terminology got a little confused between the PCI and DMA
> realms. I agree, "coherent" is better.
>
> BTW, although some EHCI controllers may support 64-bit DMA, the driver
> contains this:
>
> if (HCC_64BIT_ADDR(hcc_params)) {
> ehci_writel(ehci, 0, &ehci->regs->segment);
> #if 0
> // this is deeply broken on almost all architectures
> if (!dma_set_mask(hcd->self.controller, DMA_BIT_MASK(64)))
> ehci_info(ehci, "enabled 64bit DMA\n");
> #endif
> }
>
> I don't know if the comment is still true, but until the "#if 0" is
> removed, ehci-hcd won't make use of 64-bit DMA.

I think someone tried to remove it recently, but I wouldn't let them :)

What a mess, hopefully xhci will just take over and save the world from
this whole thing...

thanks,

greg k-h


\
 
 \ /
  Last update: 2010-04-08 02:37    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site