On Tue, Apr 3, 2018 at 9:32 AM, Michel Dänzer <michel at daenzer.net> wrote: > On 2018-04-03 03:26 PM, Ilia Mirkin wrote: >> 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. > > modprobe.blacklist=amdgpu > > works as well as the modeset parameter for this. People who build their own kernels run into trouble too. Also does this work uniformly across all systems where it is a module? The appeal of the kernel param is that it's fool-proof. > FWIW, if a new parameter or other mechanism is added for this, ideally > it should allow preventing initialization on a per-GPU basis, instead of > only per-driver, for systems with multiple GPUs supported by the same > driver. Oh yeah, that'd be nice. (Optionally though, so that it's still easy to use for the fairly common single gpu case.)
