>-----Original Message-----
>From: jan.kis...@web.de [mailto:jan.kis...@web.de] 
>Sent: Tuesday, November 10, 2009 4:22 PM
>To: Herrera-Bendezu, Luis
>Cc: xenomai-core@gna.org
>Subject: Re: rtdm_iomap_to_user with phys addr > 4GB
>
>Herrera-Bendezu, Luis wrote:
>>  
>> 
>>> -----Original Message-----
>>> From: Jan Kiszka [mailto:jan.kis...@siemens.com] 
>>> Sent: Tuesday, November 10, 2009 1:55 PM
>>> To: Herrera-Bendezu, Luis
>>> Cc: xenomai-core@gna.org
>>> Subject: Re: rtdm_iomap_to_user with phys addr > 4GB
>>>
>>>
>>> Herrera-Bendezu, Luis wrote:
>>>>  
>>>>
>>>>> -----Original Message-----
>>>>> From: Jan Kiszka [mailto:jan.kis...@siemens.com] 
>>>>> Sent: Tuesday, November 10, 2009 1:13 PM
>>>>> To: Herrera-Bendezu, Luis
>>>>> Cc: xenomai-core@gna.org
>>>>> Subject: Re: rtdm_iomap_to_user with phys addr > 4GB
>>>>>
>>>>>
>>>>> Herrera-Bendezu, Luis wrote:
>>>>>>  
>>>>>>
>>>>>>> -----Original Message-----
>>>>>>> From: Jan Kiszka [mailto:jan.kis...@siemens.com] 
>>>>>>> Sent: Tuesday, November 10, 2009 12:03 PM
>>>>>>> To: Herrera-Bendezu, Luis
>>>>>>> Cc: xenomai-core@gna.org
>>>>>>> Subject: Re: rtdm_iomap_to_user with phys addr > 4GB
>>>>>>>
>>>>>>>
>>>>>>> Herrera-Bendezu, Luis wrote:
>>>>>>>> Hello,
>>>>>>>>
>>>>>>>> I am writing an RTDM driver to replace one that uses UIO. 
>>>>> The device
>>>>>>>> resides in a physical address > 4 GB on a PPC440EPx. The 
>>> UIO could
>>>>>>>> not handle this address so I made a proposal to address it, 
>>>>>>> details at:
>>> 
>http://lists.ozlabs.org/pipermail/linuxppc-dev/2009-April/070097.html
>>>>>>>> Function rtdm_iomap_to_user() has same issue with the 
>>> physical I/O
>>>>>>>> address
>>>>>>>>    unsigned long src_addr
>>>>>>>>
>>>>>>>> I am new to Xenomai and would like to get some ideas on 
>>>>> how to solve
>>>>>>>> this
>>>>>>>> issue.
>>>>>>> I think UIO as well as RTDM suffers from the same problem 
>>> here: The
>>>>>>> kernel service used to remap the physical memory 
>(remap_pfn_range)
>>>>>>> accepts unsigned long, not phys_addr_t. How is this 
>>>>> supposed to work?
>>>>>>> Jan
>>>>>>>
>>>>>>> -- 
>>>>>>> Siemens AG, Corporate Technology, CT SE 2
>>>>>>> Corporate Competence Center Embedded Linux
>>>>>>>
>>>>>> Actually, remap_pfn_range() gets passed the physical address left
>>>>>> shifted by PAGE_SIZE in both UIO and RTDM 
>>>>> (xnarch_remap_io_page_range,
>>>>>> wrap_remap_io_page_range).
>>>>> No, the target address is expressed in pages, the source in bytes.
>>>>>
>>>> That is true for rtdm_mmap_to_user but not for 
>>> rtdm_iomap_to_user. See
>>>> how
>>>> mmap_data struct is set in both functions.
>>>        struct rtdm_mmap_data mmap_data =
>>>                { NULL, src_addr, vm_ops, vm_private_data };
>>>
>>> with src_addr = "physical I/O address to be mapped", setting
>>> mmap_data.src_paddr -- are you looking at different code?
>>>
>> No, that is the code.
>
>But there is nothing shifted, the shifting takes place in 
>Xenomai's wrapper.
>
>>> Besides this, the key is how remap_pfn_page interprets the source
>>> address argument.
>>>
>> I had used UIO with success (as described in link above). 
>The equivalent
>> code in UIO is (uio.c):
>> static int uio_mmap_physical(struct vm_area_struct *vma)
>> {
>>      struct uio_device *idev = vma->vm_private_data;
>>      int mi = uio_find_mem_index(vma);
>>      if (mi < 0)
>>              return -EINVAL;
>> 
>>      vma->vm_flags |= VM_IO | VM_RESERVED;
>> 
>>      vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>> 
>>      return remap_pfn_range(vma,
>>                             vma->vm_start,
>>                             idev->info->mem[mi].addr >> PAGE_SHIFT,
>>                             vma->vm_end - vma->vm_start,
>>                             vma->vm_page_prot);
>> }
>> 
>> where idev->info->mem[mi].addr, mem[.] is the list of 
>mappable regions.
>> Note that for UIO, the user application needs to mmap these 
>regions to
>> user space. This is a step that is not needed on RTDM, right?
>
>OK, now I got my mistake: Confused by the wrong argument names of our
>wrap_remap_io_page_range (and probably others) I thought that the
>destination is given as page number, not the source.
>
>But before adding some fancy new service for this use case, I'd like to
>understand how common it actually is (crazy embedded designs 
>tend to pop
>up and deprecate faster than such APIs...).
I do not think this is a new service but a limitation in the design.
The kernel supports it (application can mmap the device using /dev/mem)
and the PPC (440EPx in particular) has PCI and internal peripherals
located at addresses above 4 GB (I2C, SPI, etc.).
>
>And what was the final conclusion on LKML? As far as I understood the
>UIO maintainer, the proposal was rejected. Any different follow-ups on
>this that I missed? Of course, if you have a special design you can
>always patch your kernel and Xenomai to fit these special purposes. But
>for upstream support, kernel or Xenomai, it requires a clean and
>portable model.
There were no follow-ups and the reply concerning the required changes
was:
"I guess you'd have to look at the whole memory management stuff of each
 architecture to find out which kind of memory can be mapped with
addresses
 above unsigned long. Hardware often needs more than one contigous
pages.
 It might well be possible that a certain arch could have RAM for user
virtual
 addresses above 4GB, but no hardware. I don't know PPC well enough to
say
 anything about its behaviour."

In the mean time, it would be helpful if you have some suggestions on
how to
change RTDM to handle this case.

Thanks,
Luis

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