Newbie question about accessing memory in kernel space

Newbie question about accessing memory in kernel space

[Niklaus Giger]

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.

I can see the CPLD when I access the address via my Abatron BDI debugger.

In a user space test program I did a
    map_base = mmap((void *)target, nSize, PROT_READ | PROT_WRITE, MAP_SHARED, 
fd, target);
and was able to access the CPLD, too.

In user and kernel space the procedure looks like this:
void sys_set_tick_control_register_value(uint16 value)
{
    static uint16    *tickControlRegister       = (uint16*)
					HCU_TICK_CONTROL_REGISTER_ADDRESS;   
   *tickControlRegister = value;
}

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]
NIP: C302B0C4 LR: C302B350 SP: C1DABED0 REGS: c1dabe20 TRAP: 0300    Not 
tainted
MSR: 00029030 EE: 1 PR: 0 FP: 0 ME: 1 IR/DR: 11
DAR: 7D000000, DSISR: 00800000
TASK = c1d827b0[27] 'insmod' THREAD: c1daa000
Last syscall: 128
PLB0: bear= 0x04000004 acr=   0x00000000 besr=  0x00000000
PLB0 to OPB: bear= 0xef6007ff besr0= 0x00000000 besr1= 0x00000000

GPR00: C302B348 C1DABED0 C1D827B0 0000002B 00000CAC FFFFFFFF C01C0000 00029030
GPR08: C01CBB30 C3030000 00000000 7D000000 00000000 10075308 01FFBC00 007FFF77
GPR16: 00000000 00000001 10050000 00000002 7FFFFF68 10070000 00000001 C3030000
GPR24: C3030000 C3030000 FFFFFFFF 00000000 C3030000 C3030000 C0189318 C302BEC0
NIP [c302b0c4] sys_set_tick_control_register_value+0x8/0x10 [kTickTest]
LR [c302b350] init_module+0xd0/0x10c [kTickTest]
Call trace:
 [c0030954] sys_init_module+0x218/0x328
 [c0002900] syscall_dotrace_cont+0x24/0x38
Segmentation fault

What is wrong with my code? 

Any hints would be appreciated.

Thanks in advance.

Re: Newbie question about accessing memory in kernel space

[Wolfgang Grandegger]

On 05/24/2005 09:19 PM 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.
> 
> I can see the CPLD when I access the address via my Abatron BDI debugger.
> 
> In a user space test program I did a
>     map_base = mmap((void *)target, nSize, PROT_READ | PROT_WRITE, MAP_SHARED, 
> fd, target);
> and was able to access the CPLD, too.
> 
> In user and kernel space the procedure looks like this:
> void sys_set_tick_control_register_value(uint16 value)
> {
>     static uint16    *tickControlRegister       = (uint16*)
> 					HCU_TICK_CONTROL_REGISTER_ADDRESS;   
>    *tickControlRegister = value;
> }
> 
> 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]
> NIP: C302B0C4 LR: C302B350 SP: C1DABED0 REGS: c1dabe20 TRAP: 0300    Not 
> tainted
> MSR: 00029030 EE: 1 PR: 0 FP: 0 ME: 1 IR/DR: 11
> DAR: 7D000000, DSISR: 00800000
> TASK = c1d827b0[27] 'insmod' THREAD: c1daa000
> Last syscall: 128
> PLB0: bear= 0x04000004 acr=   0x00000000 besr=  0x00000000
> PLB0 to OPB: bear= 0xef6007ff besr0= 0x00000000 besr1= 0x00000000
> 
> GPR00: C302B348 C1DABED0 C1D827B0 0000002B 00000CAC FFFFFFFF C01C0000 00029030
> GPR08: C01CBB30 C3030000 00000000 7D000000 00000000 10075308 01FFBC00 007FFF77
> GPR16: 00000000 00000001 10050000 00000002 7FFFFF68 10070000 00000001 C3030000
> GPR24: C3030000 C3030000 FFFFFFFF 00000000 C3030000 C3030000 C0189318 C302BEC0
> NIP [c302b0c4] sys_set_tick_control_register_value+0x8/0x10 [kTickTest]
> LR [c302b350] init_module+0xd0/0x10c [kTickTest]
> Call trace:
>  [c0030954] sys_init_module+0x218/0x328
>  [c0002900] syscall_dotrace_cont+0x24/0x38
> Segmentation fault
> 
> What is wrong with my code? 

If the physical address is not already mapped an ioremap() is required
in kernel space.

> Any hints would be appreciated.
> 
> Thanks in advance.
> 
> _______________________________________________
> RTAI mailing list
> RTAI@rtai.org
> https://mail.rtai.org/cgi-bin/mailman/listinfo/rtai
> 
> 

Re: Newbie question about accessing memory in kernel space

[Matt Porter]

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

Re: Newbie question about accessing memory in kernel space

[Niklaus Giger]

Am Dienstag, 24. Mai 2005 22.31 schrieb Matt Porter:
> On Tue, May 24, 2005 at 09:19:28PM +0200, Niklaus Giger wrote:
> > Hi

> > 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.
ioremap() fixed my problem.

Thanks a lot for your help.

Best regards

Niklaus

Re: Newbie question about accessing memory in kernel space

[Roger Larsson]

On Tuesday 24 May 2005 21.19, 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.
>
> I can see the CPLD when I access the address via my Abatron BDI debugger.
>
> In a user space test program I did a
>     map_base = mmap((void *)target, nSize, PROT_READ | PROT_WRITE,
> MAP_SHARED, fd, target);
> and was able to access the CPLD, too.

Via 'map_base' I guess?

For kernel try
virt_base=ioremap(target, nSize)

>
> In user and kernel space the procedure looks like this:
> void sys_set_tick_control_register_value(uint16 value)
> {
>     static uint16    *tickControlRegister       = (uint16*)
> 					HCU_TICK_CONTROL_REGISTER_ADDRESS;

This indicates that you tries to read directly from an adress (no virt_base?)
You might want to use __raw_readl instead (depending on bus endianess).

/RogerL

Re: Newbie question about accessing memory in kernel space

[Niklaus Giger]

Am Mittwoch, 25. Mai 2005 01.58 schrieb Roger Larsson:
> On Tuesday 24 May 2005 21.19, 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.
> >
> > I can see the CPLD when I access the address via my Abatron BDI debugger.
> >
> > In a user space test program I did a
> >     map_base = mmap((void *)target, nSize, PROT_READ | PROT_WRITE,
> > MAP_SHARED, fd, target);
> > and was able to access the CPLD, too.
>
> Via 'map_base' I guess?
>
> For kernel try
> virt_base=ioremap(target, nSize)
Thanks this fixed my problem.
> > In user and kernel space the procedure looks like this:
> > void sys_set_tick_control_register_value(uint16 value)
> > {
> >     static uint16    *tickControlRegister       = (uint16*)
> > 					HCU_TICK_CONTROL_REGISTER_ADDRESS;
>
> This indicates that you tries to read directly from an adress (no
> virt_base?) You might want to use __raw_readl instead (depending on bus
> endianess).
__raw_readl  was not necessary.

Thanks for your help.

Best regards

Niklaus 

Re: Newbie question about accessing memory in kernel space

[David Bruce]

I was going down the same path as you are a year ago and had similar 
issues. This book covers up to 2.4 but will probably answer future 
issues you encounter:
http://www.xml.com/ldd/chapter/book/
The code in book:
http://examples.oreilly.com/linuxdrive2/