Howto allocate non-cacheable memory

Howto allocate non-cacheable memory

[Muneeswaran P - TLS, Chennai]

Hi,

How to allocate non-cacheable kernel memory ?

Pls help me.


	I am writing device driver (kernel 2.6 ) for PCI-X card.

	Pls clarify the following doubts:
	1. DPRAM is memory mapped to PCI-X card.
	2. I have to transfer data from main memory to DPRAM using bus
master concept and vice-versa.
	3. How to make this memory area as non-cacheable one ?=20
	4. Whether DMA mapping (pci_map_single() call ) should be done for
both DPRAM and main memory ?
	   4.a) I will get the physical address of DPRAM memory (memory
mapped to PCI-X card) from BAR-0 register. Can i use this physical =
addres
directly for data transer using bus master (without pci_map_single() =
call.)
?
	   4.b)  How to make main memory area as non-cacheable one ?


Regards,
Munees.
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Re: Howto allocate non-cacheable memory

[Arnd Bergmann]

On Saturday 27 May 2006 07:38, Muneeswaran P - TLS, Chennai wrote:
> =A0=A0=A0=A0=A0=A0=A0=A0Pls clarify the following doubts:
> =A0=A0=A0=A0=A0=A0=A0=A01. DPRAM is memory mapped to PCI-X card.
> =A0=A0=A0=A0=A0=A0=A0=A02. I have to transfer data from main memory to DP=
RAM using bus
> master concept and vice-versa.
> =A0=A0=A0=A0=A0=A0=A0=A03. How to make this memory area as non-cacheable =
one ?=20
> =A0=A0=A0=A0=A0=A0=A0=A04. Whether DMA mapping (pci_map_single() call ) s=
hould be done for
> both DPRAM and main memory ?
> =A0=A0=A0=A0=A0=A0=A0=A0 =A0 4.a) I will get the physical address of DPRA=
M memory (memory
> mapped to PCI-X card) from BAR-0 register. Can i use this physical addres
> directly for data transer using bus master (without pci_map_single() call=
=2E)
> ?
> =A0=A0=A0=A0=A0=A0=A0=A0 =A0 4.b) =A0How to make main memory area as non-=
cacheable one ?

You need pci_map_single() for all bus-master accesses from the PCI-X card
and ioremap() to map the card's registers and/or memory into your kernel
address space as cache-inhibited.

Depending on what your adapter does, you might want to map memory areas
on the card with __ioremap(addr, size, _PAGE_NO_CACHE) instead of
ioremap(addr, size) in order to get a non-guarded mapping.

	Arnd <><