Philippe Gerum wrote:
> On Wed, 2011-01-12 at 16:57 -0500, Herrera-Bendezu, Luis wrote:
>>> -----Original Message-----
>>> From: Gilles Chanteperdrix [mailto:[email protected]]
>>> Sent: Wednesday, January 12, 2011 3:37 PM
>>> To: Herrera-Bendezu, Luis
>>> Cc: [email protected]
>>> Subject: Re: [Xenomai-help] [Xenomai -help] User space access to DMA memory
>>>
>>> Herrera-Bendezu, Luis wrote:
>>>>> From: Gilles Chanteperdrix [mailto:[email protected]]
>>>>> Sent: Wednesday, January 12, 2011 11:26 AM
>>>>> To: Herrera-Bendezu, Luis
>>>>> Cc: [email protected]
>>>>> Subject: Re: [Xenomai-help] [Xenomai -help] User space access to DMA
>>>>> memory
>>>>>
>>>>> Herrera-Bendezu, Luis wrote:
>>>>>>> From: Gilles Chanteperdrix [mailto:[email protected]]
>>>>>>> Sent: Wednesday, January 12, 2011 8:35 AM
>>>>>>> To: Herrera-Bendezu, Luis
>>>>>>> Cc: [email protected]
>>>>>>> Subject: Re: [Xenomai-help] [Xenomai -help] User space access to DMA
>>>>>>> memory
>>>>>>>
>>>>>>> Herrera-Bendezu, Luis wrote:
>>>>>>>>> -----Original Message-----
>>>>>>>>> From: Gilles Chanteperdrix [mailto:[email protected]]
>>>>>>>>> Sent: Tuesday, January 11, 2011 6:28 PM
>>>>>>>>> To: Herrera-Bendezu, Luis
>>>>>>>>> Cc: [email protected]
>>>>>>>>> Subject: Re: [Xenomai-help] [Xenomai -help] User space access to DMA
>>>>>>>>> memory
>>>>>>>>>
>>>>>>>>> Gilles Chanteperdrix wrote:
>>>>>>>>>> Herrera-Bendezu, Luis wrote:
>>>>>>>>>>> On 01/05/2011 5:29 PM Gilles Chanteperdrix wrote:
>>>>>>>>>>>> Steven A. Falco wrote:
>>>>>>>>>>>>> On 01/05/2011 04:33 PM, Gilles Chanteperdrix wrote:
>>>>>>>>>>>> Ok. Could you try to do the same operation with the native API?
>>>>>>>>>>>> You just
>>>>>>>>>>>> have to pass H_SHARED | H_DMA | H_NONCACHED as flags to
>>>>>>>>>>>> rt_heap_create
>>>>>>>>>>>> to get the same effect as pci_dma_alloc_coherent.
>>>>>>>>>>>>
>>>>>>>>>>>> Just to see if the error lies in RTDM implementation or in Xenomai
>>>>>>>>>>>> generic code.
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>> (...)
>>>>>>>>>> What about the other thing I asked you to test?
>>>>>>>>>>
>>>>>>>>> Ping? Any news about this test?
>>>>>>>> rt_heap_create() with flags H_SHARED | H_DMA | H_NONCACHED report
>>>>>>>> -EINVAL.
>>>>>>>> Documentation indicates that H_NONCACHE is not compatible with H_DMA.
>>>>>>> Right, supporting H_NONCACHED | H_DMA would mean that we would have to
>>>>>>> use kmalloc/get_free_pages then establish a non-cached mapping in
>>>>>>> kernel-space with vm_map_ram.
>>>>>>>
>>>>>>> Could you try with H_NONCACHED, but without H_DMA? Of course, the
>>>>>>> mapping can not be used for DMA, as it will probably not be physically
>>>>>>> contiguous, but at least you can try whether accessing in user-space a
>>>>>>> non-cached mapping works.
>>>>>> It does work but unless an external unit writes to heap memory it would
>>>>>> be difficult to verify that the non-cached memory actually works, i.e.
>>>>>> access from user space gets expected value(s).
>>>>> I am quite confident this works.
>>>>>
>>>>>>> In any case, we see a defect in the RTDM interface here: we can not ask
>>>>>>> the mapping to be mapped non-cacheable, which somewhat defeats the
>>>>>>> purpose of pci_alloc_consistent. I do not know enough the powerpc
>>>>>>> architecture to know whether this could be the cause of your issue (the
>>>>>>> same physical area mapped twice, once cached, once non-cached). However,
>>>>>>> on the ARM architecture, for instance, it is bad.
>>>>>>>
>>>>>> Let me summarize the ideas discussed so far to allocate consistent memory
>>>>>> suitable for DMA and corresponding mapping to user space:
>>>>>> * rt_heap cannot be created with both H_NONCACHED and H_DMA. But it is
>>>>>> automatically mapped to user space with rt_heap_bind().
>>>>>>
>>>>>> A solution can be to allocate heap with H_SHARED | H_DMA, somehow
>>>>>> get bus address of single block of memory (rt_heap { sba } ?) to
>>>>>> used for DMA operations.
>>>>> The test with rt_heap was just a test to have a comparison between
>>>>> xnheap code and rtdm_mmap. But we may indeed want to fix mmappable
>>>>> xnheaps later on.
>>>>>
>>>>>> * RTDM interface rtdm_mmap/unmap cannot handle non-cacheable memory.
>>>>>>
>>>>>> A solution can be to allocate GFP_DMA memory with kmalloc(), use
>>>>>> rtdm_mmap to map to user space. Programmatically make memory
>>>>>> consistent before/after DMA transfer to/from external unit, e.g.
>>>>>> dma_sync_single_for_device()/dma_sync_single_for_cpu(). This is
>>>>>> similar to what streaming DMA mappings do.
>>>>>>
>>>>>> * Ideally, it should be possible to take memory allocated from
>>>>>> dma_alloc_coherent()/pci_alloc_consistent() and mapped it to
>>>>>> user space using rtdm_mmap().
>>>>> To check that the non-cacheable mapping is indeed the problem, here is a
>>>>> patch which adds the possibility to add non-cacheable mappings:
>>>>>
>>>>> diff --git a/ksrc/skins/rtdm/drvlib.c b/ksrc/skins/rtdm/drvlib.c
>>>>> index 3495e63..ec0ddae 100644
>>>>> --- a/ksrc/skins/rtdm/drvlib.c
>>>>> +++ b/ksrc/skins/rtdm/drvlib.c
>>>>> @@ -1791,6 +1791,7 @@ void rtdm_nrtsig_pend(rtdm_nrtsig_t *nrt_sig);
>>>>>
>>>>> #if defined(CONFIG_XENO_OPT_PERVASIVE) || defined(DOXYGEN_CPP)
>>>>> struct rtdm_mmap_data {
>>>>> + int noncached;
>>>>> void *src_vaddr;
>>>>> phys_addr_t src_paddr;
>>>>> struct vm_operations_struct *vm_ops;
>>>>> @@ -1815,6 +1816,9 @@ static int rtdm_mmap_buffer(struct file *filp,
>>>>> struct vm_area_struct *vma)
>>>>> maddr = vma->vm_start;
>>>>> size = vma->vm_end - vma->vm_start;
>>>>>
>>>>> + if (mmap_data->noncached)
>>>>> + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
>>>>> +
>>>>> #ifdef CONFIG_MMU
>>>>> /* Catch vmalloc memory (vaddr is 0 for I/O mapping) */
>>>>> if ((vaddr >= VMALLOC_START) && (vaddr < VMALLOC_END)) {
>>>>> @@ -1975,6 +1979,24 @@ int rtdm_mmap_to_user(rtdm_user_info_t *user_info,
>>>>> void *vm_private_data)
>>>>> {
>>>>> struct rtdm_mmap_data mmap_data = {
>>>>> + .noncached = 0,
>>>>> + .src_vaddr = src_addr,
>>>>> + .src_paddr = 0,
>>>>> + .vm_ops = vm_ops,
>>>>> + .vm_private_data = vm_private_data
>>>>> + };
>>>>> +
>>>>> + return rtdm_do_mmap(user_info, &mmap_data, len, prot, pptr);
>>>>> +}
>>>>> +
>>>>> +int rtdm_mmap_noncached_to_user(rtdm_user_info_t *user_info,
>>>>> + void *src_addr, size_t len,
>>>>> + int prot, void **pptr,
>>>>> + struct vm_operations_struct *vm_ops,
>>>>> + void *vm_private_data)
>>>>> +{
>>>>> + struct rtdm_mmap_data mmap_data = {
>>>>> + .noncached = 1,
>>>>> .src_vaddr = src_addr,
>>>>> .src_paddr = 0,
>>>>> .vm_ops = vm_ops,
>>>>> @@ -2043,6 +2065,7 @@ int rtdm_iomap_to_user(rtdm_user_info_t *user_info,
>>>>> void *vm_private_data)
>>>>> {
>>>>> struct rtdm_mmap_data mmap_data = {
>>>>> + .noncached = 0,
>>>>> .src_vaddr = NULL,
>>>>> .src_paddr = src_addr,
>>>>> .vm_ops = vm_ops,
>>>>>
>>>>> Simply call rtdm_mmap_noncached_to_user instead of rtdm_mmap_to_user.
>>>>>
>>>> Get same kernel panic error as before with this patch. I need to look
>>>> closer
>>>> at what are the memory allocation functions used by pci_ and dma_.
>>> Could you try rtdm_iomap_to_user (but beware, pass the physical address
>>> returned by pointer by pci_alloc_consistent)? virt_to_page, or __pa will
>>> not work with vmalloc/ioremap addresses. And pci_alloc_consistent
>>> probably returns a vmalloc mapping due to the fact that the mapping
>>> needs to be non-cacheable, which will happen if your powerpc does not
>>> support cache snooping, and define CONFIG_NOT_COHERENT_CACHE.
>>>
>> Your suggestion works. Can you highlight why it fails when using
>> rtdm_mmap_to_user()?
>
> Because unlike the former, it does not get the right platform-dependent
> protection bits for the vma from phys_mem_access_prot() for this kind of
> memory.
There is another issue: the memory returned by pci_alloc_consistent
should be handled as vmalloc memory, but it is allocated in a separated
area, the CONSISTENT_BASE, CONSISTENT_END area. So the test:
if ((vaddr >= VMALLOC_START) && (vaddr < VMALLOC_END))
returns false, and the memory is handled as if it were kmalloced memory.
--
Gilles.
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