Re: [PATCH v5 1/1] iommu-api: Add map_sg/unmap_sg functions

[Olav Haugan <ohaugan-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 8/18/2014 11:32 AM, Rob Clark wrote:
> On Mon, Aug 18, 2014 at 10:07 AM, joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org <joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org> wrote:
>> On Tue, Aug 12, 2014 at 09:56:11AM -0700, Olav Haugan wrote:
>>> On 8/12/2014 3:48 AM, Rob Clark wrote:
>>>> iirc, one plan for 'flags' was some sort of DONT_FLUSH_TLB flag for
>>>> drivers which wanted to map/unmap N buffers with a single flush at the
>>>> end.  There might have been some other usages envisioned.
>>>
>>> Yes, that was the original intent of the flags for now. I am sure we can
>>> find other uses for this in the future.
>>
>> Do you have anything else in mind already besides the DONT_FLUSH_TLB
>> flag?

No, I do not have other uses right now. But could imagine use cases like
"force <insert minimum mapping size here> mapping" flag etc.

>> How is the IOTLB supposed to be flushed when this flag is used?
>>
> 
> well, I was thinking one of two ways:
> 
> 1) add new flush() vfunc.. this, I think, would be most convenient for
> drivers using this feature
> 2) or driver simply doesn't set DONT_FLUSH_TLB flag on the last
> {map,unmap}..  that would be slightly more awkward to use, but would
> avoid adding a new vfunc
> 

I agree and would support adding a public flush() API. It is cleaner.
However, it does allow clients to chose which method to use. Either an
extra call to flush() or just do not pass DONT_FLUSH_TLB flag on the
last invocation of map/unmap.


Thanks,

Olav

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