mmap KSEG1

mmap KSEG1

[Ed Okerson]

Is it possible to mmap an address in KSEG1 so a user space app can
read/write to an IO device uncached?

Ed

Re: mmap KSEG1

[David Daney]

Ed Okerson wrote:
> Is it possible to mmap an address in KSEG1 so a user space app can
> read/write to an IO device uncached?
> 

It depends on your definition of 'possible'.  The mips32/64 architecture 
specification has a 'C' field in the EntryLo register that controls 
cachability, so given an appropriate device driver it should be doable.

Calling  __ioremap() with the appropriate flags should allow you to set 
the 'C' bits.

Depending on your requirements, you might be able to get by using 
/dev/mem and some 'sync' instructions, instead of establishing an 
uncached mapping.


David Daney

Re: mmap KSEG1

[Thomas Bogendoerfer]

On Fri, Dec 04, 2009 at 11:52:03AM -0600, Ed Okerson wrote:
> Is it possible to mmap an address in KSEG1 so a user space app can
> read/write to an IO device uncached?

well not exactly to KSEG1, since that is kernel exclusive address space,
but it's possible to map the physical address of the device:

Try

fd = open("/dev/mem", O_RDWR|O_SYNC);
io = mmap (NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, ioaddr);

where ioaddr is the physical address of the io device.

Thomas.

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