Re: [PATCH] fbdev: Remove udlfb driver

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Am 02.12.20 um 08:55 schrieb Thomas Zimmermann:
> 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. :/
>
> I guess we (DRM devs) have to treat fbdev as the solution for use cases 
> such as ours.

s/ours/yours

> 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

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