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

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Message-ID: <de9b257e-1ce1-c5ca-b3b4-8fce369361a7@daenzer.net>
Date:   Tue, 13 Dec 2016 16:18:49 +0900
From:   Michel Dänzer <michel@...nzer.net>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Teddy Wang <teddy.wang@...iconmotion.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Arnaud Patard <arnaud.patard@...-net.org>
Subject: Re: [RFC PATCH 0/3] staging: remove fbdev drivers

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
there.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer