Messages in this thread | | | From | Michael Buesch <> | Subject | Re: DMA debug trace pointing to rtl8187 | Date | Sat, 9 May 2009 22:19:39 +0200 |
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On Saturday 09 May 2009 21:29:59 Greg KH wrote: > On Sat, May 09, 2009 at 12:29:27PM -0500, Larry Finger wrote: > > I think there is a second problem that John's fix does not treat. Although the > > buffer is removed from the stack, there is no assurance that the buffer obtained > > with kmalloc() is reachable by DMA. This case will be triggered if the USB > > adapter does 32-bit DMA and the system has more than 4 GB RAM.
In practice this does not hit, because such systems' kmalloc does not return memory above 4G (i386) _or_ the DMA mapping functions take care of bounce buffering or I/O-remapping (should be true for all other arches). So if the device is able to do DMA with addresses >=32bit it should be fine, provided it correctly sets the DMA mask.
> Memory returned by kmalloc will always be able to be DMAable. If not, > we have lots of problems :)
True for sane devices. False for devices like Broadcom HND-DMA, which should only be used to slap thy hw engineers.
-- Greetings, Michael.
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