# Re: Problem with framebuffer mmap on platforms with large addressing

- From: Dmitry Eremin-Solenikov \<hidden\>
- Date: 2012-04-09 16:18:29 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2012/04/9469080
- Thread: https://ratatoskr.run/linux-fbdev/2012/03/9468884/t.md

```text
On Tue, Mar 20, 2012 at 9:40 AM, Benjamin Herrenschmidt
[ref] wrote:
>
>> >> That is interesting! Are those patches published or otherwise available
>> >> somewhere? We are also very interested in enabling Canyonlands
>> >> with Radeon KMS!
>> >
>> > You will run into additional problems with 460 due to the fact that it's
>> > not cache coherent for DMA. Tony patches don't address that part of the
>> > problem (they were used on a 476 based platform).
>>
>> Hmm. Could you please spill a little bit more of details? Also are those patches
>> for 476 merged or present somewhere?
>
> Well, DMA on 46x isn't cache coherent. The DRM plays interesting games
> with mapping/unmapping pages for DMA by the chip and I don't think we
> have the right hooks to do the appropriate cache flushing on these guys,
> but Tony might be able to comment, I don't know whether he tried or not.
>
> On the other hand 476 has fully cache coherent DMA so the only problem
> there is the >32-bit physical address space.
>
> As for the patches, you'll have to wait for Tony to respond (I'll poke
> him locally).

Any news on these patches? A dirty and "not for the upstream yet" version
would be sufficient for me for now.

>
> Cheers,
> Ben.
>

-- 
With best wishes
Dmitry
```