Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752887Ab0H1QTH (ORCPT ); Sat, 28 Aug 2010 12:19:07 -0400 Received: from metis.ext.pengutronix.de ([92.198.50.35]:41564 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752284Ab0H1QTF (ORCPT ); Sat, 28 Aug 2010 12:19:05 -0400 Date: Sat, 28 Aug 2010 18:18:58 +0200 From: Sascha Hauer To: Marek Vasut Cc: linux-arm-kernel@lists.infradead.org, Linus Walleij , Dan Williams , linux-kernel@vger.kernel.org, Uwe =?iso-8859-15?Q?Kleine-K=F6nig?= Subject: Re: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support Message-ID: <20100828161858.GI1473@pengutronix.de> References: <1281956870-12463-1-git-send-email-s.hauer@pengutronix.de> <20100823174852.GB26928@pengutronix.de> <201008281727.10913.marek.vasut@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <201008281727.10913.marek.vasut@gmail.com> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 17:45:16 up 56 days, 6:56, 6 users, load average: 0.48, 0.35, 0.23 User-Agent: Mutt/1.5.18 (2008-05-17) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:215:17ff:fe12:23b0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2021 Lines: 44 On Sat, Aug 28, 2010 at 05:27:10PM +0200, Marek Vasut wrote: > Dne So 28. srpna 2010 17:18:17 Linus Walleij napsal(a): > > 2010/8/23 Uwe Kleine-K?nig : > > >> + 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. Nope, this has nothing to do with static mappings vs. ioremap. The difference is that read[b,w,l] do little endian accesses suitable for PCI whereas the __raw_* functions do accesses in CPU endianess. Peripherals integrated into a SoC like the SDMA engine here are normally accessible in native endianess and thus need the __raw_* functions. An external network controller (for example a LAN9117) will probably need the non raw functions. Note that 99% of the arm users use little endian only and thus cpu_to_le* is a noop, so both types will work for most people. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/