linux-kernel - Re: DMA APIs gumble grumble

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Date:	Thu, 09 Nov 2006 19:01:43 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	benh@...nel.crashing.org
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

From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Date: Fri, 10 Nov 2006 13:55:27 +1100

> > pci_alloc_consistent() is not allowed from atomic contexts.
> 
> Yes, but some drivers did it anyway, though I can't remember under which
> circumstances (IDE probe possibly ? It's a usual culprit for that sort
> of thing). This is why most implementations use GFP_ATOMIC (including
> sparc64 :-)

Ok, I see.

> Oh well, I have no problem with leaving sparc32 do GFP_KERNEL indeed, I
> can't remember for sure the reason why we have most architectures do
> GFP_ATOMIC, but it probably never hit sparc32.

I wish sparc32 hadn't used alloc_resource() as a poor-man's bitmap
allocator to keep track of IOMMU mappings.  That's where the
GFP_KERNEL requirement comes from.

Just use GFP_KERNEL for now, and someone might find the strength
to remove this problem some day :-)
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