Hi Am 02.11.23 um 07:45 schrieb Simon Lees:
Hi,
Sorry I missed this thread while I was travelling
On 10/10/23 18:56, Thomas Zimmermann via openSUSE Factory wrote:
tl;dr: Disable fbdev userspace interfaces on TW
Hi,
the upcoming Linux kernel v6.6 will contain the option to disable fbdev userspace interfaces in the kernel configuration. [1] I intent to enable this and thereby switch off /dev/fb0 et al. The tracker bug is boo#1212947. [2]
* Why? The old fbdev subsystem is an endless source of bugs. For example, we recently had an out-of-bounds access in the fbdev emulation, where userspace could write beyond the end of the framebuffer memory. [3] Fbdev is under-maintained. I've been doing improvements in recent kernel releases, but only where it benefits the DRM subsystem. Disabling fbdev userspace interfaces will also help weeding out any programs that still contain hard dependencies on them.
* What changes? Enabling the new kernel option disables all fbdev userspace interfaces. These are
* the device files, such as /dev/fb0 * the sys files under /sys/class/graphics/fb[0-9]+ * /proc/fb
* What are the effects on userspace programs? Userspace applications run on the desktop via Wayland or X. There will be no change to them. Xorg and Wayland compositors run on DRM interfaces. A few programs run on SDL, which has no dependency on fbdev either. Any fbdev support in these mid-layer components should be disabled as well.
There's one known affected program: TW's text-mode installer can use the tool fbiterm to display CJK symbols during installation. This comes from a time when some low-end systems where not able to boot graphics installation. fbiterm has been unmaintained for >15 years and is ready for retirement. But there's no good drop-in replacement. I propose to simply remove fbiterm and let the graphics installer handle CJK.
* What about the framebuffer console? The kernel-provided framebuffer console does not change. The kernel will still show the regular console. Userspace interfaces in /sys/class/graphics/fbcon are still available.
For questions and discussion, please comment here or in boo#1212947. I have usecases with raspberry pi's and other similar devices where I have used SPI based TFT displays outputting directly to /dev/fb0, In particular I have used "fbi" to draw images directly to the framebuffer, efl (Enlightenment Foundation Libraries) apps can also render directly to the framebuffer.
I haven't had mine working that recently so I can't comment on the state of the driver I was using but given the prevalence of such devices in the raspberry pi ecosystem it probably makes alot of sense to keep this feature enabled atleast for ARM kernels.
Which displays (brand, model) do you use? Do you need a new driver for the displays? Or do you need a user space that does not require /dev/fb? Best regards Thomas
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)