linux-kernel - Re: [PATCH 2/2] dma: mv_xor: Use high

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Date:	Tue, 29 Oct 2013 10:32:29 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	sachin.kamat@...aro.org, Vinod Koul <vinod.koul@...el.com>,
	dmaengine@...r.kernel.org
Subject: Re: [PATCH 2/2] dma: mv_xor: Use high_base mmio where appropriate

Dan, Ezequiel,

On Tue, 29 Oct 2013 05:34:08 -0300, Ezequiel Garcia wrote:

> > On Mon, Oct 28, 2013 at 3:54 PM, Ezequiel Garcia
> > <ezequiel.garcia@...e-electrons.com> wrote:
> > > Despite requesting two memory resources, called 'base' and 'high_base', the
> > > driver uses explicitly only the former. The latter is being used implicitly
> > > by addressing at offset +0x200, which in practice accesses high_base.
> > >
> > > Instead of relying in such trick, let's define the registers with the
> > > offset from high_base, and use high_base explicitly where appropriate.
> > >
> > > Signed-off-by: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
> > > ---
> > >  drivers/dma/mv_xor.c |  3 ++-
> > >  drivers/dma/mv_xor.h | 25 +++++++++++++------------
> > >  2 files changed, 15 insertions(+), 13 deletions(-)
> > 
> > Since it's unused I'd prefer a patch that just deletes xor_high_base.
> > 
> 
> It's wrongly *unused*, the mmio high_base is actually being used
> implicitly by always addressing at an offset that addresses +200.
> 
> Deleting high_base would actually make it worse, for that region
> will no longer be ioremaped. Maybe the commit message is not clear
> about it?

I agree with Ezequiel, and I believe his patch is appropriate. The
registers for the XOR engines are indeed split in two areas, so it
makes sense to have this xor_base / xor_high_base split that reflects
the register mapping passed from the Device Tree, and use this split in
the macros used to access the registers.

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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