Re: [Xenomai-core] User-space DMA transfer and I/O access from Xenomai API

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

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Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>  > Merilainen, Jussi (GE Healthcare) wrote:
>  > >  
>  > > 
>  > > I'm porting a PCI driver for a custom board from VxWorks to Xenomai/Linux. My goal is to keep the driver as much as possible in user-space. Implementing the HW interrupt handler should be quite straight forward as presented in 'Writing user-space device drivers' in Native-API-Tour manual.
>  > > My concern is the PCI DMA transfer. Does the Xenomai API provide any support for this in user-space? Does anyone have experience on this subject?
>  > 
>  > Actually, this need not be a Xenomai-specific issue. User space device
>  > drivers are of increasing common interest in the Linux community. I only
>  > collected some projects so far, I did not dig into the APIs:
>  > 
>  > - libpci as part of the pciutils provides ways to access device
>  >   information, don't know if it also allows to map DMA memory to user
>  >   space.
> 
> libpci allow user-space to retrieve the bus addresses of memory
> regions of each PCI device. Mmaping this memory may be done using
> /dev/mem. But usually, PCI devices do DMA the other way around: they are
> passed the physical address of some RAM, become bus-master and write
> directly to this RAM. So what is needed is:
> - to map some physically contiguous RAM region to user-space;
> - get the physical addres of this region in order to pass it to the PCI
>   device to program the DMA.
> 
> Xenomai allow you to map to user-space some physically contiguous RAM
> region (using either native heaps or posix shared memory smaller than
> 128K), but does not provide accessors to the RAM physical
> address. Is it what you need ?
> 

I think we are primarily looking for some user space
dma_map_*/dma_unmap_* support here - which also has to be RT-safe.

Jan


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