linux-kernel - Re: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support

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Message-Id: <201008281727.10913.marek.vasut@gmail.com>
Date:	Sat, 28 Aug 2010 17:27:10 +0200
From:	Marek Vasut <marek.vasut@...il.com>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Linus Walleij <linus.ml.walleij@...il.com>,
	"Uwe Kleine-König" 
	<u.kleine-koenig@...gutronix.de>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support

Dne So 28. srpna 2010 17:18:17 Linus Walleij napsal(a):
> 2010/8/23 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>:
> >> +     evt = readl(SDMA_H_EVTOVR);
> >> +     mcu = readl(SDMA_H_HOSTOVR);
> >> +     dsp = readl(SDMA_H_DSPOVR);
> > 
> > __raw_readl?
> 
> Sorry I never understood this __raw_[read|write][b|w|l] vs.
> plain read[b|w|l] proliferation in some drivers and code.
> 
> What's the reason for?

Hey,

this trick is, if you create the VA<->PA mapping at the kernel start (eg. see 
how pxa_map_io() is replacedon some devices for instance), you then use the VA 
address you specified and use __raw_{read,write}[b,w,l](). So use 
__raw_{read,write}[b,w,l]() on drivers specific for certain device and use 
{read,write}[b,w,l]() on ioremap()ed memory areas, aka. in common drivers.

Cheers

> 
> Yours,
> Linus Walleij
> 
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> linux-arm-kernel@...ts.infradead.org
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