little endian page mapping on PQ3

little endian page mapping on PQ3

[Jose Almeida]

Hi all,

Looking at PQ3 documentation, it looks like there is a way to select
on a page basis if we would like to map one particular page in BIG or
LITTLE endian.
This is a very nice feature when you need to exchange some data
between a PC and a PQ3 target.

I am wondering if someone have already tryed this PQ3 feature ?
I guess this would require some kind of hook in the kernel ...

Any clue ?

Thanks -  Jose

RE: little endian page mapping on PQ3

[Joyeau Sylvain]

Jose,

You are right, PQ3 supports endianess choice on a per page basis.=20
Without any hook in Linux, you can remap physical address range (but =
RAM), by calling __ioremap() with the "_PAGE_ENDIAN" bit set in the =
flags.

--
sj

> -----Original Message-----
> From:=20
> linuxppc-embedded-bounces+sylvain.joyeau=3Dthomson.net@ozlabs.or
> g=20
> [mailto:linuxppc-embedded-bounces+sylvain.joyeau=3Dthomson.net@o
> zlabs.org] On Behalf Of Jose Almeida
> Sent: vendredi 24 ao=FBt 2007 09:59
> To: Linuxppc-embedded@ozlabs.org
> Subject: little endian page mapping on PQ3
>=20
> Hi all,
>=20
> Looking at PQ3 documentation, it looks like there is a way to select
> on a page basis if we would like to map one particular page in BIG or
> LITTLE endian.
> This is a very nice feature when you need to exchange some data
> between a PC and a PQ3 target.
>=20
> I am wondering if someone have already tryed this PQ3 feature ?
> I guess this would require some kind of hook in the kernel ...
>=20
> Any clue ?
>=20
> Thanks -  Jose
>=20
> _______________________________________________
> Linuxppc-embedded mailing list
> Linuxppc-embedded@ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-embedded
>=20

Re: little endian page mapping on PQ3

[Jose Almeida]

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Re: little endian page mapping on PQ3

[Clemens Koller]

Hi, Jose!

Jose Almeida schrieb:
> Hi all,
> 
> Looking at PQ3 documentation, it looks like there is a way to select
> on a page basis if we would like to map one particular page in BIG or
> LITTLE endian.
> This is a very nice feature when you need to exchange some data
> between a PC and a PQ3 target.

I would be interested, however cannot spend time right now to work
on that subject.

> I am wondering if someone have already tryed this PQ3 feature ?
> I guess this would require some kind of hook in the kernel ...

Just some random bits I found in the web:
http://developer.apple.com/documentation/Hardware/DeviceManagers/pci_srvcs/pci_cards_drivers/PCI_BOOK.250.html

The Interesting part is:
"Thus, the address swizzle is completely transparent to software."

So, I would just try to setup some memory mapping and turn on little endian
mode to access that area... MMMV. Just a guess.

Regards,
-- 
Clemens Koller
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Re: little endian page mapping on PQ3

[David Hawkins]

Hi Jose,

> I want to do using an mmap() entry point in a driver, in order to map 
> this to the user. Of course in that case ioremap() does not work.
> 
> Any Clue ?
> 

I used the little-endian flag on the Yosemite board (440EP)
to test what the flag did.

http://www.ovro.caltech.edu/~dwh/correlator/pdf/LNX-762-Hawkins.pdf
http://www.ovro.caltech.edu/~dwh/correlator/software/driver_design.tar.gz

Look at the mmap function in pci_io.c.

	/* PowerPC endian control
	 * - default is cleared, big-endian
	 */
#ifdef _PAGE_ENDIAN
	if (bar->little_endian) {
		pgprot_val(vma->vm_page_prot) |= _PAGE_ENDIAN;
	} else {
		pgprot_val(vma->vm_page_prot) &= ~_PAGE_ENDIAN;
	}
	if (pgprot_val(vma->vm_page_prot) & _PAGE_ENDIAN) {
		LOG_DEBUG("_PAGE_ENDIAN is set\n");
	} else {
		LOG_DEBUG("_PAGE_ENDIAN is not set\n");
	}
#endif

It might be the same for the PQ3 ... at least it'll be
pretty similar.

Dave