On Sat, Jul 24, 2021 at 1:56 PM Arnd Bergmann <arnd@xxxxxxxxxx> wrote: > > On Sat, Jul 24, 2021 at 11:55 AM Karol Herbst <kherbst@xxxxxxxxxx> wrote: > > > > On Sat, Jul 24, 2021 at 8:55 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote: > > > > > > On Sat, Jul 24, 2021 at 12:47 AM Karol Herbst <kherbst@xxxxxxxxxx> wrote: > > > > > > > > In the past this only led to compilation issues. Also the small amount of > > > > extra .text shouldn't really matter compared to the entire nouveau driver > > > > anyway. > > > > > > > > > > > select DRM_TTM_HELPER > > > > - select BACKLIGHT_CLASS_DEVICE if DRM_NOUVEAU_BACKLIGHT > > > > - select ACPI_VIDEO if ACPI && X86 && BACKLIGHT_CLASS_DEVICE && INPUT > > > > + select BACKLIGHT_CLASS_DEVICE > > > > + select ACPI_VIDEO if ACPI && X86 && INPUT > > > > select X86_PLATFORM_DEVICES if ACPI && X86 > > > > select ACPI_WMI if ACPI && X86 > > > > > > I think the logic needs to be the reverse: instead of 'select > > > BACKLIGHT_CLASS_DEVICE', > > > this should be 'depends on BACKLIGHT_CLASS_DEVICE', and the same for ACPI_VIDEO. > > > > > > We may want to add 'default DRM || FB' to BACKLIGHT_CLASS_DEVICE in the > > > process so we don't lose it for users doing 'make oldconfig' or 'make defconfig' > > > > > > > I think the problem with > > "depends" is that the user needs to enable backlight support first > > before even seeing nouveau and I don't know if that makes sense. But > > maybe "default" is indeed helping here in this case. > > In general, no driver should ever 'select' a subsystem. Otherwise you end up > with two problems: > > - enabling this one driver suddenly makes all other drivers that have > a dependency > on this visible, and some of those might have a 'default y', so you > end up with > a ton of stuff in the kernel that would otherwise not be there. > > - It becomes impossible to turn it off as long as some driver has that 'select'. > This is the pretty much the same problem as the one you describe, just > the other side of it. > > - You run into dependency loops that prevent a successful build when some > other driver has a 'depends on'. Preventing these loops was the main > reason I said we should do this change. > > In theory we could change the other 85 drivers that use 'depends on' today, > and make BACKLIGHT_CLASS_DEVICE a hidden symbol that only ever > selected by the drivers that need it. This would avoid the third problem but > not the other one. > > Arnd > I see. Yeah, I guess we can do it this way then. I just wasn't aware of the bigger picture here. Thanks for explaining.
