[PATCH] fbdev: Remove udlfb driver

[Daniel Vetter]

On Wed, Dec 2, 2020 at 8:55 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>
> Hi
>
> Am 01.12.20 um 12:20 schrieb Mikulas Patocka:
> >
> >
> > On Tue, 1 Dec 2020, Thomas Zimmermann wrote:
> >
> >> Hi
> >>
> >> Am 30.11.20 um 19:39 schrieb Mikulas Patocka:
> >>>
> >>>
> >>> On Mon, 30 Nov 2020, Daniel Vetter wrote:
> >>>
> >>>> On Mon, Nov 30, 2020 at 09:31:15AM -0500, Mikulas Patocka wrote:
> >>>>>
> >>>>> The framebuffer driver supports programs running full-screen directly on
> >>>>> the framebuffer console, such as web browser "links -g", image viewer
> >>>>> "fbi", postscript+pdf viewer "fbgs", ZX Spectrum emulator "fuse-sdl",
> >>>>> movie player "mplayer -vo fbdev". The DRM driver doesn't run them.
> >>>>
> >>>> Hm this should in general work on drm drivers. Without that it's clear the
> >>>> switch-over isn't really ready yet.
> >>>
> >>> I fixed it with this patch two years ago:
> >>> https://lists.freedesktop.org/archives/dri-devel/2018-June/179023.html
> >>>
> >>> But the patch never went through and the fb_defio feature was removed in
> >>> the kernel 5.6 (commit d0c4fc5a4814e431c15272935c8dc973c18073aa).
> >>>
> >>>
> >>> Without fb_defio, the only other possibility how to update the screen is
> >>> the ioctl DRM_IOCTL_MODE_DIRTYFB. But this ioctl requires master mode, so
> >>> user programs like "links -g" can't issue it.
> >>
> >> That's confusing. DIRTYFB is only for DRM.
> >
> > Yes, you're right.
> >
> >> And why can links not run as DRM master mode? If it renders to the terminal,
> >> it should act like a composer. In that case it almost certainly wants master
> >> status.
> >>
> >> Best regards
> >> Thomas
> >
> > How can a userspace program acquire master mode without being suid?
>
> For my understanding, there's no easy solution to that. :/

If you're absolutely the only thing running, the first one to open the
card* node wins. But usually you have something like logind managing
this for you (for vt switching), since ad-hoc this is a very fragile
scheme.

I'm not exactly sure how logind gives you an already opened drm device
in master mode, that's a bit tricky. Without either being suid root or
participating in the logind scheme you won't be able to vt switch
though.

But bare metal kms usage should work I as-is.
-Daniel

>
> I guess we (DRM devs) have to treat fbdev as the solution for use cases
> such as ours.
>
> For the unplug issue, I'll try to reproduce and fix it.
>
> For the performance problems, we might be able to squeeze a few more
> cycles out of it.
>
> Best regards
> Thomas
>
> >
> > Is there some "Hello World!" program that shows how to use DRM? I'm not an
> > expert in DRM, but if there were some tutorial+documentation, I could
> > consider porting "links" to it.
> >
> > Mikulas
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch