On Tue, Apr 3, 2018 at 5:29 AM, Daniel Vetter <daniel at ffwll.ch> wrote: > On Sun, Apr 01, 2018 at 10:12:10PM +0200, Christian König wrote: >> Am 01.04.2018 um 20:21 schrieb Takashi Iwai: >> > On Sun, 01 Apr 2018 19:58:11 +0200, >> > Christian K6nig wrote: >> > > Am 01.04.2018 um 19:45 schrieb Ilia Mirkin: >> > > > On Sun, Apr 1, 2018 at 1:39 PM, Christian König >> > > > <christian.koenig at amd.com> wrote: >> > > > > Am 30.03.2018 um 22:45 schrieb Takashi Iwai: >> > > > > > amdgpu driver lacks of modeset module option other drm drivers provide >> > > > > > for enforcing or disabling the driver load. Interestingly, the >> > > > > > amdgpu_mode variable declaration is already found in the header file, >> > > > > > but the actual implementation seems to have been forgotten. >> > > > > > >> > > > > > This patch adds the missing piece. >> > > > > NAK, modesetting is mandatory for amdgpu and we should probably remove the >> > > > > option to disable it from other DRM drivers without UMS support as well >> > > > > (pretty much all of them now). >> > > > > >> > > > > If you want to prevent a driver from loading I think the correct way to do >> > > > > so is to give modprobe.blacklist=amdgpu on the kernel commandline. >> > > > > >> > > > > That would remove the possibility to prevent the driver from loading when it >> > > > > is compiled in, but I don't see much of a problem with that. >> > > > Having a way to kill the graphics driver is a very useful debugging >> > > > tool, and also a quick and easy way to get out of an unpleasant >> > > > situation where graphics are messed up / system hangs / etc. The >> > > > modprobe blacklist kernel arg only works in certain environments (and >> > > > only if it's a module). >> > > > >> > > > Every other DRM driver has this and this is a well-documented >> > > > workaround for "graphics are messed up when I install linux", why not >> > > > allow a uniform experience for the end users who are just trying to >> > > > get their systems up and running? >> > > Because it is not well documented and repeated over and over again in >> > > drivers. >> > > >> > > The problem is that people don't realized that the driver isn't loaded >> > > at all without the modeset=0 module option and demand fixing the >> > > resulting bad performance without modesetting. >> > Hm, I don't get it. What this options has to do with performance for >> > a KMS-only driver...? >> >> Well exactly that's the point, nothing. >> >> The problem is that the option name is confusing to the end user because the >> expectation is that "nomodeset" just means that they only can't change the >> display mode. >> >> Some (unfortunately quite a lot) people don't realize that for KMS drivers >> this means that the driver isn't even loaded and they also don't get any >> acceleration. >> >> We had to explain that numerous times now. I think it would be best to give >> the option a more meaningful name. > > Yeah, agreed with Christian. If we want a generic "pls disable all gfx > accel" knob then probably best to put that into the drm core. And just > outright fail loading the drm core if that happens, which will prevent all > gfx drivers from loading. > > That likely means a hole bunch of stuff won't work (usually sound keels > over too), but that's what you get for this. Only disabling modesetting > without disabling the entire driver doesn't work (never has, except for > this UMS+GEM combo only i915 support, and not for long). > > And once we have that knob, probably best to phase out all the per-driver > options. Another use-case that the per-driver disables enable is "i915 works but nouveau is broken due to crazy ACPI / PCIe PM / whatever". It seems likely this could happen with amdgpu as well. The current set of capabilities has served developers fairly well in providing quick debug instructions to mildly-experienced users (i.e. enough to be able to edit kernel cmdline). I definitely wouldn't want to lose that. The names are horrid. I think everyone agrees. In fact, when the driver is disabled by nomodeset or modeset=0, I think they should print like "driver completely disabled by modeset option" to avoid some of the user confusion Christian is referring to (which I've run into on a number of occasions as well). And/or maybe just refuse the driver load entirely rather than load-but-do-nothing. However being able to help users debug things seems more important than users being occasionally confused by options they added to kernel cmdline. -ilia
