Re: [RFC PATCH 0/3] staging: remove fbdev drivers

From: Michel DÃnzer
Date: Tue Dec 13 2016 - 02:19:23 EST

On 10/12/16 05:27 AM, Benjamin Herrenschmidt wrote:
> On Fri, 2016-12-09 at 14:35 +0100, Daniel Vetter wrote:
>>> As for multi userspace client, well, swapping an mmap between HW and
>>> memory backing store is a somewhat solved problem already.
>> Hm, I didn't know that, but then all existing drm drivers have fairly
>> simplistic fbdev mmap implementations.
> Hrm, I though the TTM did it ... I remember talking with Thomas
> Hellstrom about that back in the day... you use unmap_mapping_range
> to unmap the existing mappings basically so you can take new faults
> and route them to a different page, but I can't see a call in there
> so maybe he ended up not doing it.

I think he did, it was working fine for userspace mappings when I tried
making radeon use a non-pinned BO for fbdev years ago (the problem was
fbcon potentially trying to access the framebuffer at the most
inconvenient times). There's still ttm_fbdev_mmap, but I'm not sure
everything to make this fully work for userspace fbdev mappings is still

Earthling Michel DÃnzer |
Libre software enthusiast | Mesa and X developer