Re: [Xenomai-core] User space drivers on PPC440

["Steven A. Falco" <sfalco@domain.hid>]

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Your patch makes sense.

I have some results, but I'm not sure I understand what they mean.  I've 
attached the test program that I am using.  Here is what it outputs:

bash-3.00# ./o2
Trying to free nonexistent resource <0000000000000000-00000000c0000001>
get leds: -16 Device or resource busy
put leds: 0 Success

Trying to free nonexistent resource <0000000000000000-ffffffffffffffff>
get low_mem: -16 Device or resource busy
put low_mem: 0 Success

I am a little unclear on request_resource() - the return code is 
backwards of what I would have expected.  Looking at examples in the 
kernel, it appears that request_resource() returns EBUSY when things go 
well, and it returns 0 when things go badly.  Like I said, that seems 
backwards, but I guess it makes sense - EBUSY apparently means that the 
resource is _now_ busy?

Anyway, following the kernel examples, my program considers a non-zero 
return as success.  At that point I release the region.  If instead, I 
get a zero return, then I treat that as a failure, and don't release the 
region.

The part I don't understand is why I get the "Trying to free nonexistent 
resource" messages.  Since I am getting an EBUSY, I thought that meant I 
owned the resource, and that I should release it...

Also, the addresses printed above are a bit strange.  For example, I 
would have thought that instead of 
"<0000000000000000-00000000c0000001>", it would print 
"<00000001c0000000-00000001c0000013>".  Perhaps that is a clue - maybe 
the start and length are not being passed correctly.

One more question.  It appears that if my program crashes, that the 
region will never be released.  So, the normal behavior of an exiting 
process freeing all its resources doesn't seem to be guaranteed.

    Steve


Philippe Gerum wrote:
> Philippe Gerum wrote:
>   
>> Steven A. Falco wrote:
>>     
>>> The rt_misc_get_io_region() has the "start" argument as an unsigned 
>>> long.  On the PPC440, we have a 36-bit address space, where the I/O 
>>> registers are generally above the 4GB area.  For example, the UART is at 
>>> address 0x1ef600300.
>>>
>>> The Linux request_region call has "start" typed as a resource_size_t, 
>>> which is a u64 on the PPC440 (i.e. CONFIG_RESOURCES_64BIT is set even 
>>> though this is a 23-bit processor).
>>>
>>> Is this something that should be handled by xeno-config?  It could 
>>> append a CFLAG indicating the size of a resource.
>>>       
>> Or use a 64bit long unconditionally, to keep the same kernel-based
>> implementation, since there is no performance issue for this call. In
>> any case, we need to fix the API before 2.4 final is out -- which will
>> also affect the ABI, but it already changed during the 2.4 development
>> phase anyway.
>>
>>     
>
> Does this patch work for you?
>
>   

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#include <fcntl.h>
#include <posix/pthread.h>
#include <posix/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

#include <native/task.h>
#include <native/timer.h>

#define LED 0x1c0000002ULL
#define LEN 13
#define BS 128

test_it(unsigned long long addr, unsigned long len, char *name)
{
        int rv_get;
        int rv_put;
        char *bp;
        char buf[BS];

        rv_get = rt_misc_get_io_region(addr, len, name);
        if(rv_get) {
                rv_put = rt_misc_put_io_region(addr, len);
        }

        bp = strerror_r(-rv_get, buf, BS);
        fprintf(stderr, "get %s: %d %s\n", name, rv_get, bp);

        bp = strerror_r(-rv_put, buf, BS);
        fprintf(stderr, "put %s: %d %s\n", name, rv_put, bp);
}

main()
{
        test_it(LED, LEN, "leds");
        test_it(0, LEN, "low_mem");
}