Re: Newbie question about accessing memory in kernel space

On Tue, May 24, 2005 at 09:19:28PM +0200, Niklaus Giger wrote:

Hi

I am working on a custom PPC405 board where I have a 2.6.10 kernel with RTAI 
patches (fusion) running.

I am trying to access some custom CPLD chip hanging at 0x7D000000. In my 
intial board (hcu3_map_io) I added a corresponding io_block_mapping.

Is a "corresponding" mapping a 1:1 mapping? Don't do that.  You cannot
map stuff that way since it is below TASK_SIZE i.e. it's in user address
space, not kernel address space.

Now I compiled a module which tries to access the CPLD during the insmod phase
and I get the following output.

Oops: kernel access of bad area, sig: 11 [#1]

<snip>

What is wrong with my code? 

You mapped the device into user virtual address space.  The TLB
replacement code is unable to load a TLB entry for a page outside
of kernel space...so you crash.

Don't use io_block_map()...it allows you to shoot yourself in the
foot very easily (as you just witnessed). Use ioremap() to map
your device.

-Matt

Am Dienstag, 24. Mai 2005 22.31 schrieb Matt Porter:

On Tue, May 24, 2005 at 09:19:28PM +0200, Niklaus Giger wrote:

quoted

Hi

quoted

Oops: kernel access of bad area, sig: 11 [#1]

<snip>

quoted

What is wrong with my code?

You mapped the device into user virtual address space.  The TLB
replacement code is unable to load a TLB entry for a page outside
of kernel space...so you crash.

Don't use io_block_map()...it allows you to shoot yourself in the
foot very easily (as you just witnessed). Use ioremap() to map
your device.

ioremap() fixed my problem.

Thanks a lot for your help.

Best regards

Niklaus