Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> writes: Hello Geert and Thomas, > Hi Thomas, > > On Wed, Jun 7, 2023 at 5:15 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: >> Am 07.06.23 um 10:48 schrieb Geert Uytterhoeven: >> > On Mon, Jun 5, 2023 at 4:48 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: >> >> --- a/drivers/video/fbdev/Kconfig >> >> +++ b/drivers/video/fbdev/Kconfig >> >> @@ -57,6 +57,15 @@ config FIRMWARE_EDID >> >> combination with certain motherboards and monitors are known to >> >> suffer from this problem. >> >> >> >> +config FB_DEVICE >> >> + bool "Provide legacy /dev/fb* device" >> > >> > Perhaps "default y if !DRM", although that does not help for a >> > mixed drm/fbdev kernel build? >> >> We could simply set it to "default y". But OTOH is it worth making it a >> default? Distributions will set it to the value they need/want. The very >> few people that build their own kernels to get certain fbdev drivers >> will certainly be able to enable the option by hand as well. > > Defaulting to "n" (the default) means causing regressions when these > few people use an existing defconfig. > Having "dfault y if !DRM" makes sense to me. I guess is a corner case but at least it won't silently be disabled for users that only want fbdev as Geert mentioned. I wouldn't call it a regression though, because AFAIK the Kconfig options are not a stable API ? >> > Or reserve "FB" for real fbdev drivers, and introduce a new FB_CORE, >> > to be selected by both FB and DRM_FBDEV_EMULATION? >> > Then FB_DEVICE can depend on FB_CORE, and default to y if FB. Funny that you mention because it's exactly what I attempted in the past: https://lore.kernel.org/all/20210827100531.1578604-1-javierm@xxxxxxxxxx/T/#u >> >> That wouldn't work. In Tumbleweed, we still have efifb and vesafb >> enabled under certain conditions; merely for the kernel console. We'd >> have to enable CONFIG_FB, which would bring back the device. > > "Default y" does not mean that you cannot disable FB_DEVICE, so > you are not forced to bring back the device? > I think we can have both to make the kernel more configurable: 1) Allow to only disable fbdev user-space APIs (/dev/fb?, /proc/fb, etc), which is what the series is doing with the new FB_DEVICE config symbol. 2) Allow to disable all "native" fbdev drivers and only keep the DRM fbdev emulation layer. That's what my series attempted to do with the FB_CORE Kconfig symbol. I believe that there are use cases for both, for example as Thomas' said many distros are disabling all the fbdev drivers and their user-space only requires DRM/KMS, so makes sense to not expose any fbdev uAPI at all. But may be that other users want the opposite, they have an old user-space that requires fbdev, but is running on newer hardware that only have a DRM driver. So they will want DRM fbdev emulation but none fbdev driver at all. That's why I think that FB_DEVICE and FB_CORE are complementary and we can support any combination of the two, if you agree there are uses for either. -- Best regards, Javier Martinez Canillas Core Platforms Red Hat
