linux-kernel - Re: [PATCH 2/8] dmaengine: mv_xor: add support for a38x command in descriptor mode

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Message-ID: <3020836.4xH6fTICuR@wuerfel>
Date:	Tue, 12 May 2015 18:03:34 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Lior Amsalem <alior@...vell.com>, Andrew Lunn <andrew@...n.ch>,
	Jason Cooper <jason@...edaemon.net>,
	Vinod Koul <vinod.koul@...el.com>, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Petazzoni <thomas@...e-electrons.com>,
	linux-crypto@...r.kernel.org,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 2/8] dmaengine: mv_xor: add support for a38x command in descriptor mode

On Tuesday 12 May 2015 17:54:31 Thomas Petazzoni wrote:
> Dear Arnd Bergmann,
> 
> On Tue, 12 May 2015 17:49:08 +0200, Arnd Bergmann wrote:
> 
> > Using 
> > 
> >       if (IS_ENABLED(__BIG_ENDIAN))
> > 
> > here would make it more readable by avoiding the #if. Alternatively,
> > you could leave the XOR_DESCRIPTOR_SWAP flag disabled and just swap
> > the descriptors manually like a lot of other drivers do. You have
> > to swap the mmio accesses anywya.
> 
> Agreed on IS_ENABLED(). However, I don't understand the comment about
> the need to swap mmio accesses? We're using readl_relaxed() /
> writel_relaxed(), and they do the swapping already. Am I missing
> something?
> 

Sorry for being unclear. This was exactly my point: readl_relaxed()
has to do swaps internally, and you can also do swaps when accessing
the descriptor in memory.

	Arnd
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