Re: [Xenomai-core] pgprot_noncached for io-remapping?

[Philippe Gerum <rpm@xenomai.org>]

Jan Kiszka wrote:
> Philippe Gerum wrote:
>> Jan Kiszka wrote:
>>> Philippe Gerum wrote:
>>>> Jan Kiszka wrote:
>>>>> Hi,
>>>>>
>>>>> doesn't this patch [1] have some relevance for us as well? As we use
>>>>> xnarch_remap_io_page_range also for non-IO memory, I'm hesitating to
>>>>> suggest that we apply this unconditionally at xnarch level. Ideas welcome.
>>>>>
>>>> Yes, I think it makes a lot of sense on powerpc at least, since doing so will
>>>> set the PAGE_GUARDED bit as well, and we obviously want to avoid any
>>>> out-of-order access of I/O memory.
>>>>
>>>> (I don't see the reason to force the VM_RESERVED and VM_IO on the vma though,
>>>> since remap_pfn_range will do it anyway.)
>>> No, I was talking about cases where we may pass kmalloc'ed memory to
>>> xnarch_remap_io_page_range. In that case, caching and out-of-order
>>> access may be desired for performance reasons.
>>>
>> xnarch_remap_io_page_range is intended for I/O memory only, some assumptions are
>> made on this. rtdm_mmap_buffer() should be fixed; it would be much better to
>> define another internal interface at xnarch level to specifically perform
>> kmalloc mapping.
> 
> Yeah, probably. But I think the issue is not just limited to RTDM. The
> xnheap can be kmalloc-hosted as well.
>

This one is used with DMA memory. What I would suggest, is something like this:

--- ksrc/skins/rtdm/drvlib.c	(revision 3590)
+++ ksrc/skins/rtdm/drvlib.c	(working copy)
@@ -1738,9 +1738,12 @@
 		}
 		return 0;
 	} else
-#endif /* CONFIG_MMU */
 		return xnarch_remap_io_page_range(vma, maddr, paddr,
 						  size, PAGE_SHARED);
+#else
+	return xnarch_remap_kmem_page_range(vma, maddr, paddr,
+					    size, PAGE_SHARED);
+#endif /* CONFIG_MMU */
 }

 static struct file_operations rtdm_mmap_fops = {


I.e. split the cases where MMU is absent from the one where MMU is there but we
come from rtdm_iomap_to_user.

> Jan
> 


-- 
Philippe.