Re: [Xenomai-help] rtdm_iomap_to_user on PPC

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

Philippe Gerum wrote:
> Gilles Chanteperdrix wrote:
>> Alexis Berlemont wrote:
>>> Hi,
>>>
>>> On Friday 17 October 2008 06:46, thomas.debes@domain.hid wrote:
>>>> No comments or ideas? Providing this feature is essential for our CPCI
>>>> drivers. We have to port some Linux applications to Xenomai which use that
>>>> mmap stuff intensely.
>>>>
>>>> Thanks again!
>>>>
>>>> Thomas
>>>>
>>>>> -----Ursprüngliche Nachricht-----
>>>>> Von: xenomai-help-bounces@domain.hid
>>>>> [mailto:xenomai-help-bounces@domain.hid] Im Auftrag von
>>>>> thomas.debes@domain.hid
>>>>> Gesendet: Mittwoch, 8. Oktober 2008 11:49
>>>>> An: xenomai@xenomai.org
>>>>> Betreff: [Xenomai-help] rtdm_iomap_to_user on PPC
>>>>>
>>>>> Hello,
>>>>>
>>>>> in the following thread I was asking for a solution to use
>>>>> rtdm_iomap_to_user() on PPC (MPC5200, Denx 2.4.25)
>>> In 2.4 kernel, rtdm_iomap_to_user() is based on the function remap_page_range 
>>> (with vma->vm_flags |= VM_RESERVED).
>>>
>>> Once, I had to develop a classical Linux driver (for PPC) which provided mmap 
>>> functionalites so as to let a user application mmap a buffer allocated thanks 
>>> to __get_free_pages().
>>>
>>> On a 2.6 kernel, I used remap_pfn_range() and it works great but on 2.4 kernel 
>>> the function remap_page_range() did not work as I expected. I had a quick 
>>> look on its implementation and I found that instead of mapping my buffer it 
>>> mapped newly allocated zeroed pages (if my memories are correct).
>>>
>>> If I remember well, these pages were allocated in lazy mode. That could 
>>> explain the freeze of your whole system: in case a RT application in primary 
>>> mode tries to access the mmapped buffer.
>> Well, normally, the fault should cause the RT application to switch to
>> secondary mode and be handled gracefully from there, unless there is a
>> bug hidden in Xenomai or I-pipe. Besides, RT applications usually use
>> "mlockall", so the kernel should make all the pages present and not rely
>> on further faults (at least, is it how it works on 2.6).
>>
> 
> powerpc may still trigger minor faults upon TLB misses though. That arch has a
> software-assisted MMU.

Ok, and can these faults cause lockups when they happen in primary mode?

-- 
					    Gilles.