linux-kernel - Re: [PATCH 1/2] arm: mvebu: increase atomic coherent pool size for armada 370/XP

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Message-ID: <20121025160928.53daf18a@skate>
Date:	Thu, 25 Oct 2012 16:09:28 +0200
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Andrew Lunn <andrew@...n.ch>,
	linux-arm-kernel@...ts.infradead.org,
	Olof Johansson <olof@...om.net>,
	Ben Dooks <ben-linux@...ff.org>,
	Ian Molton <ian.molton@...ethink.co.uk>,
	Nicolas Pitre <nico@...xnic.net>,
	Lior Amsalem <alior@...vell.com>,
	Maen Suleiman <maen@...vell.com>,
	Tawfik Bayouk <tawfik@...vell.com>,
	Shadi Ammouri <shadi@...vell.com>,
	"Eran Ben-Avi" <benavi@...vell.com>,
	Yehuda Yitschak <yehuday@...vell.com>,
	Nadav Haklai <nadavh@...vell.com>,
	Ike Pan <ike.pan@...onical.com>,
	Jani Monoses <jani.monoses@...onical.com>,
	Chris Van Hoof <vanhoof@...onical.com>,
	Dan Frazier <dann.frazier@...onical.com>,
	Leif Lindholm <leif.lindholm@....com>,
	Jon Masters <jcm@...hat.com>,
	David Marlin <dmarlin@...hat.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 1/2] arm: mvebu: increase atomic coherent pool size for
 armada 370/XP


On Thu, 25 Oct 2012 13:46:41 +0000, Arnd Bergmann wrote:

> > Seems like the driver is too lazy and allocates everything coherent
> > to avoid the hassle of doing dma_map/dma_unmap operations when
> > needed, but I haven't looked in details at the driver yet to see if
> > it would be possible to switch those DMA coherent allocations into
> > non-coherent allocations + appropriate calls to the DMA operations.
> 
> Using coherent allocations is fine, I was wondering whether they need
> to be atomic or not.

You're raising a good point here: all the dma_pool_alloc()
allocations done by sata_mv are GFP_KERNEL. So why are we having
problems with the /atomic/ coherent pool size? Is it the libata core
that's doing GFP_ATOMIC DMA coherent allocations. It doesn't seem so.
Something's odd.

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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