linux-kernel - Re: [patch 2.6.23-rc1] dma_free_coherent() needs irqs enabled (sigh)

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Date:	Tue, 24 Jul 2007 16:08:11 -0700
From:	David Brownell <david-b@...bell.net>
To:	Russell King <rmk+lkml@....linux.org.uk>
Cc:	Linux Kernel list <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>
Subject: Re: [patch 2.6.23-rc1] dma_free_coherent() needs irqs enabled (sigh)

On Tuesday 24 July 2007, Russell King wrote:
> 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.

This little "to do" list item has been sitting in my mailbox way
too long then.  Certainly since it was fair to say "last year"!  ;)

Of course, 2.6.23-rc1 also merges all the gadget API updates I
included to cope with this annoyance.  So with any luck the issue
will now finally have been properly whupped.


> Signed-off-by: Russell King <rmk+kernel@....linux.org.uk>

Thanks...

 
> > 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.

Right, I noticed that.

- Dave
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