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

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Date:	Thu, 25 Oct 2012 13:46:41 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
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 Thursday 25 October 2012, Thomas Petazzoni wrote:
> On Thu, 25 Oct 2012 11:27:36 +0000, Arnd Bergmann wrote:
> > On Wednesday 24 October 2012, Gregory CLEMENT wrote:
> > > For Armada 370/XP we have the same problem that for the commit
> > > cb01b63, so we applied the same solution: "The default 256 KiB
> > > coherent pool may be too small for some of the Kirkwood devices, so
> > > increase it to make sure that devices will be able to allocate their
> > > buffers with GFP_ATOMIC flag"
> > > 
> > > Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
> > 
> > Do you know why the ATA driver needs this? I find it surprising that
> > it's necessary, so I'd like to make sure we're not just working around
> > a device driver bug here.
> 
> The sata_mv driver create dma_pool and allocate objects from them, and
> all the memory allocated for dma_pools is allocated using
> dma_alloc_coherent(), and I guess the driver is using too much of them.
> 
> 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.

> That said, that's for sure a larger task than just enabling SATA on
> Armada 370/XP, so I would advocate to handle this problem separately.

Agreed.

	Arnd
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