Re: Inefficient PCI DMA usage (was: [experimental patch] UHCI updates)

[Russell King <rmk@arm.linux.org.uk>]

Hi,

You may have already found out that there's a problem using
pci_alloc_consistent and friends in the USB layer which will
only be obvious on CPUs where they need to do page table remapping
- that is that pci_alloc_consistent/pci_free_consistent aren't
guaranteed to be interrupt-safe.

I'm not sure what the correct way around this is yet, but I do
know its a major problem. ;(

Maybe we need to do a get_free_pages-type thing with this and
keep a set amount of consistent area in reserve for atomic
allocations (as per GFP_ATOMIC)?  Yes, I know its not nice, but
I don't see any other option at the moment with USB.

(yes, I'm hacking the 2.2.18 ohci driver for my own ends to get
something up and running on one of my machines).
   _____
  |_____| ------------------------------------------------- ---+---+-
  |   |         Russell King        rmk@arm.linux.org.uk      --- ---
  | | | | http://www.arm.linux.org.uk/personal/aboutme.html   /  /  |
  | +-+-+                                                     --- -+-
  /   |               THE developer of ARM Linux              |+| /|\
 /  | | |                                                     ---  |
    +-+-+ -------------------------------------------------  /\\\  |
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