linux-kernel - Re: DMA APIs gumble grumble

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Date:	Fri, 10 Nov 2006 12:02:04 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	David Miller <davem@...emloft.net>
Cc:	linux-input@...ey.karlin.mff.cuni.cz, linux-kernel@...r.kernel.org,
	paulus@...ba.org, anton@...ba.org, greg@...ah.com
Subject: Re: DMA APIs gumble grumble

> 
> Please just mirror what I did on sparc64 for sparc32, see changeset
> 42f142371e48fbc44956d57b4e506bb6ce673cd7, with followup bug fixes
> in 36321426e320c2c6bc2f8a1587d6f4d695fca84c and
> 7233589d77fdb593b482a8b7ee867e901f54b593.

Question about sparc. It's implementation of pci_alloc_consistent(),
unlike the other ones from before we had a GFP mask massed, does
GFP_KERNEL allocations and not GFP_ATOMIC. Thus it's never expected to
be called in atomic context. In fact, it does various other things like
calling allocate_resource which is not something you ever want to be
called from interrupt context.

I'm splitting it into a pci_do_alloc_consistent that takes a gfp arg,
and a pair of pci_alloc_consistent & dma_alloc_consistent wrappers.

Do you think I should have the former pass GFP_KERNEL like the current
implementation does or switch it to GFP_ATOMIC like everybody does ? In
this case, should I also change the kmalloc done in there to allocate a
struct resource to use the gfp argument ? (It's currently doing
GFP_KERNEL).

Cheers,
Ben.

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