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

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

[-- Attachment #1: Type: text/plain, Size: 3980 bytes --]

Philippe Gerum wrote:
> Jan Kiszka wrote:
>> Philippe Gerum wrote:
>>> Jan Kiszka wrote:
>>>> Philippe Gerum wrote:
>>>>> 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.
>>>> Makes no sense to me yet. With CONFIG_MMU we have 3 cases, not just two,
>>>> no? We have to use mmap_data->src_paddr to tell kmem_page apart from
>>>> io_page.
>>> That's what the patch I sent right after this one does.
>> Nope, vaddr can be NULL in both cases, only paddr is differentiating.
>>
>> This one should do what we need:
>>
>> Index: ksrc/skins/rtdm/drvlib.c
>> ===================================================================
>> --- ksrc/skins/rtdm/drvlib.c	(Revision 3594)
>> +++ ksrc/skins/rtdm/drvlib.c	(Arbeitskopie)
>> @@ -1739,8 +1739,12 @@ static int rtdm_mmap_buffer(struct file 
>>  		return 0;
>>  	} else
>>  #endif /* CONFIG_MMU */
>> +	if (mmap_data->src_paddr)
>>  		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);
>>  }
>>  
>>  static struct file_operations rtdm_mmap_fops = {
>>
>>
> 
> Ok. So if that's fine with you, I think we should merge that because the current
> situation is error-prone.

Will do, patches for 2.3..trunk in stand-by for now. Do you have a
xnarch_remap_kmem_page_range definition at hand?

> 
> For the time being, I've defined a remap_kmem wrapper which mirrors the previous
> actions of the remap_io one, before I fixed the latter with the noncache
> protection bits. At least we should get the same behaviour than previously wrt
> to rtdm_mmap_buffer. This leaves some time to think about the kmem mapping modes
> without breaking the current situation, but they should be correct now.
> 

OK.

Jan


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 254 bytes --]