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Date: Tue, 27 Feb 2007 17:36:22 +0300 From: "Alexey Zaytsev" <alexey.zaytsev@...il.com> To: "Kyle McMartin" <kyle@...artin.ca> Cc: "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org> Subject: Re: ioread32 endianess. On 2/27/07, Kyle McMartin <kyle@...artin.ca> wrote: > On Tue, Feb 27, 2007 at 08:20:21AM -0500, Kyle McMartin wrote: > > PCI is always little endian, unless it's not. In which case you're probably PCI is always LE, but the host may be different. If you read some data from a PCI device on a LE host, the data would be OK, but on a BE host, you may need to swap it. Right? More fun comes when you are doing DMA... > > dealing with a graphics card which likely has some kind of palindromic > > register which you can read and write to set the endianness of the host > > interface. Whoo. Run on sentence. > > > > Perhaps we should have a Documentation/ entry for this... > > io(read|write){8,16,32} are the "pci iomap" functions (see > asm-generic/iomap.h) they always byteswap so the value is little endian. They do even if the target bus is not little endian, right? > > io(read|write){8,16,32}be are sister functions added to deal with big > endian busses. They always byteswap so the value is in big endian. > > Both these previous functions can handle using a cookie based on an IO port > range, or an MMIO region. > > (read|write){b,w,l} are the old style MMIO-mapped accessors. They also always > byteswap so the value is in little endian. There is no big endian equivalent > for the generic case. > > __raw_(read|write){b,w,l} are also old style accessors. They always operate > in host endianness. > > The above are (AFAIK) the only functions guaranteed to exist for MMIO. > > Of course, most platforms either provide (in|out){b,w,l} or don't support > Port IO as well, but MMIO is the really complicated case. > > In any event, <asm-generic/iomap.h> should shed a bit more light on using > these. > > Cheers, > Kyle M. > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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