On Tue, Jul 24, 2007 at 02:29:05PM -0700, David Brownell wrote:
> On at least ARM (and I'm told MIPS too) dma_free_coherent() has a newish
> call context requirement: unlike its dma_alloc_coherent() sibling, it
> may not be called with IRQs disabled. (This was new behavior on ARM as
> of late 2006, caused by ARM SMP updates.)
I think you got the year wrong:
5edf71ae (Russell King 2005-11-25 15:52:51 +0000 364) WARN_ON(irqs_disabled());
which is due to this commit:
[ARM] Do not call flush_tlb_kernel_range() with IRQs disabled.
We must not call TLB maintainence operations with interrupts disabled,
otherwise we risk a lockup in the SMP IPI code.
This means that consistent_free() can not be called from a context with
IRQs disabled. In addition, we must not hold the lock in consistent_free
when we call flush_tlb_kernel_range(). However, we must continue to
prevent consistent_alloc() from re-using the memory region until we've
finished tearing down the mapping and dealing with the TLB.
Therefore, leave the vm_region entry in the list, but mark it inactive
before dropping the lock and starting the tear-down process. After the
mapping has been torn down, re-acquire the lock and remove the entry
from the list.
Signed-off-by: Russell King <[email protected]>
> Since it looks like that restriction won't be removed, this patch changes
> the definition of the API to include that requirement.
The PCI DMA-mapping API had this restriction. For some reason, this
restriction was not carried forward into the DMA-API. Unfortunately
the restriction can not be removed without causing the problems
described in the commit which introduced it.
Or alternatively we scrap ARM SMP entirely, which isn't going to happen.
--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of:
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