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

On Tue, 7 Oct 2025, Thomas Zimmermann wrote:

Hi

Am 03.10.25 um 21:50 schrieb Helge Deller:

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On 10/3/25 20:43, sukrut heroorkar wrote:

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On Thu, Oct 2, 2025 at 8:52 AM Thomas Zimmermann [off-list ref]
wrote:

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Am 02.10.25 um 08:41 schrieb Helge Deller:

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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