Re: [PATCH] fbdev: udlfb: make CONFIG_FB_DEVICE optional

[Mikulas Patocka <mpatocka@redhat.com>]

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On Tue, 7 Oct 2025, Thomas Zimmermann wrote:

> Hi
> 
> Am 03.10.25 um 21:50 schrieb Helge Deller:
> > On 10/3/25 20:43, sukrut heroorkar wrote:
> > > On Thu, Oct 2, 2025 at 8:52 AM Thomas Zimmermann <tzimmermann@suse.de>
> > > wrote:
> > > > Am 02.10.25 um 08:41 schrieb Helge Deller:
> > > > > > > > kernel test robot noticed the following build errors:
> > > > > > > 
> > > > > > > Did you compile and test this code before submitting this patch?
> > > > > > 
> > > > > > Yes, I had compiled & loaded the udlfb module with no errors. Please
> > > > > > let me know how to proceed in this case.
> > > > > 
> > > > > Look at the reported build error, which seems to happen in dev_dbg().
> > > > > So, maybe in your testing you did not have debugging enabled?
> > > > > The report contains the .config file with which you can test.
> > > > 
> > > > Can we rather make an effort to remove the udlfb driver entirely? A few
> > > > years back, there was one user who was still using it because of some
> > > > problems with the DRM udl driver. But I think we've addressed them. The
> > > > discussion is at [1].

It was me - and I am still using it on an ARM64 MacchiatoBIN board because 
the board doesn't have graphics output.

The problems with the UDL DRM driver were:

* crashes with full-screen framebuffer applications, such as "links2 -g", 
"fbi" or "fbgs". On UDLFB, there are no crashes.

* worse performance - the UDL DRM driver updates everything in a given 
rectangle, while the UDLFB driver keeps back-buffer and front-buffer and 
updates only differences between them.

* crash when you unplug the card while Xorg was running (already fixed)

Mikulas