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.
--
Gilles.
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