Re: [Xenomai-help] RTDM mmap alternative

[Jan Kiszka <jan.kiszka@domain.hid>]

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Rodrigo Rosenfeld Rosas wrote:
> Hi, Jan. I think I wasn't very clear on my post. I'll try to clarify
> what I meaned...
> 
> Jan Kiszka escreveu:
>> Rodrigo Rosenfeld Rosas wrote:
>>  
>>> Hi Jan, I'm back on this discussion.
>>>
>>> At the time I asked you, you told me to do the mmap on driver
>>> initialization.
>>>
>>> But now, I realized that, since I'll be using RTDM, how could I use
>>> mmap from RTDM, even if in a non RT-context?
>>>     
>>
>> Which mapping step are you now referring to, the one to get the large
>> physical DMA area inside the kernel address space or the one to map
>> kernel addresses to user space?
> I'm refering to the second case. I want to map the kernel addresses to
> user space but I'm not very sure if I can do the same thing I did in my
> previous mmap call on an ioctl. I mean, I don't know if the kernel does
> something else in a mmap call... And since I don't have a mmap handler
> I'm a bit confusing...
> 
>>  Already checked the related LDD3 chapter for this?
>>   
> Yes, but it didn't answered to my doubts...

What precisely? I suggested to look at remap_pfn_range() or
io_remap_page_range(). Do you see problems when using one of them?

>>> I'm a bit confusing...
>>>
>>> What would be others alternatives for avoid copying the video frames
>>> in a RTDM driver?
>>>     
>>
>> Either map or copy, there is no third way. The point is just which
>> mapping functions to use and when.
>>   
> That is what I would like to know... Which mapping functions are
> available? Actually, if I can use the same I used on my previous mmap
> handler that is good. I'm just unsure if something will be missing or
> not...

As I haven't written such a driver as well yet, I cannot say which one
will fit. You will have to go though the LDD explanations and play with
it (which means e.g. finding out where to obtain all required arguments
- should be feasible).

> 
> I have also noted that there is no poll or select handler on RTDM. Are
> there some plans to include them?
> 

Only rough plans. This requires a lot of work and restructuring, I'm
afraid. And I doubt that it's worth it. Do you see an urgent use-case
for poll/select under RT? The only real-life use-case that we came
across was ACE/TAO.

Jan


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