linux-kernel - Re: DMABOUNCE in pci-rcar

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Message-Id: <201402251644.01463.arnd@arndb.de>
Date:	Tue, 25 Feb 2014 16:44:01 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Magnus Damm <magnus.damm@...il.com>
Cc:	"Russell King - ARM Linux" <linux@....linux.org.uk>,
	Magnus Damm <damm@...nsource.se>, linux-pci@...r.kernel.org,
	Simon Horman <horms+renesas@...ge.net.au>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"SH-Linux" <linux-sh@...r.kernel.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>
Subject: Re: DMABOUNCE in pci-rcar

On Tuesday 25 February 2014, Magnus Damm wrote:
> And the DMABOUNCE code does not support HIGHMEM, so because of that
> the block layer BOUNCE is also used.

Ah, I misunderstood this part previously. I understand better what's
going on now, but this also enforces the impression that both BOUNCE
and DMABOUNCE are not what you should be doing here.

On a related note, I've had some more discussions with Santosh on IRC,
and I think he's in the exact same position on mach-keystone, so we
should make sure that whatever solution either of you comes up with
also works for the other one.

The situation on keystone may be a little worse even, because all their
DMA masters have a 2GB limit, but it's also possible that the same
is true for you. Which categories of DMA masters do you have on R-Car?

a) less than 32-bit mask, with IOMMU
b) less than 32-bit mask, without IOMMU
c) 32-bit mask
d) 64-bit mask

	Arnd
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