Messages in this thread | | | From | Marek Vasut <> | Subject | Re: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support | Date | Sat, 28 Aug 2010 18:30:05 +0200 |
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Dne So 28. srpna 2010 18:18:58 Sascha Hauer napsal(a): > 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-König <u.kleine-koenig@pengutronix.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. > > 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.
Sorry, you got me here. Why do we have io{read,write} then btw. ? That's for x86's io space, right ?
Thanks, cheers and sorry for the confusion > > Sascha -- 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/
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