On Wed, 03 Jul 2024 14:42:37 +0200 Dragan Simic <dsimic@xxxxxxxxxxx> wrote: > Hello everyone, > > On 2024-06-17 22:17, Dragan Simic wrote: > > Panfrost DRM driver uses devfreq to perform DVFS, while using > > simple_ondemand > > devfreq governor by default. This causes driver initialization to fail > > on > > boot when simple_ondemand governor isn't built into the kernel > > statically, > > as a result of the missing module dependency and, consequently, the > > required > > governor module not being included in the initial ramdisk. Thus, let's > > mark > > simple_ondemand governor as a softdep for Panfrost, to have its kernel > > module > > included in the initial ramdisk. > > > > This is a rather longstanding issue that has forced distributions to > > build > > devfreq governors statically into their kernels, [1][2] or has forced > > users > > to introduce some unnecessary workarounds. [3] > > > > For future reference, not having support for the simple_ondemand > > governor in > > the initial ramdisk produces errors in the kernel log similar to these > > below, > > which were taken from a Pine64 RockPro64: > > > > panfrost ff9a0000.gpu: [drm:panfrost_devfreq_init [panfrost]] > > *ERROR* Couldn't initialize GPU devfreq > > panfrost ff9a0000.gpu: Fatal error during GPU init > > panfrost: probe of ff9a0000.gpu failed with error -22 > > > > Having simple_ondemand marked as a softdep for Panfrost may not resolve > > this > > issue for all Linux distributions. In particular, it will remain > > unresolved > > for the distributions whose utilities for the initial ramdisk > > generation do > > not handle the available softdep information [4] properly yet. > > However, some > > Linux distributions already handle softdeps properly while generating > > their > > initial ramdisks, [5] and this is a prerequisite step in the right > > direction > > for the distributions that don't handle them properly yet. > > > > [1] > > https://gitlab.manjaro.org/manjaro-arm/packages/core/linux/-/blob/linux61/config?ref_type=heads#L8180 > > [2] https://salsa.debian.org/kernel-team/linux/-/merge_requests/1066 > > [3] https://forum.pine64.org/showthread.php?tid=15458 > > [4] > > https://git.kernel.org/pub/scm/utils/kernel/kmod/kmod.git/commit/?id=49d8e0b59052999de577ab732b719cfbeb89504d > > [5] > > https://github.com/archlinux/mkinitcpio/commit/97ac4d37aae084a050be512f6d8f4489054668ad > > > > Cc: Diederik de Haas <didi.debian@xxxxxxxxx> > > Cc: Furkan Kardame <f.kardame@xxxxxxxxxxx> > > Cc: stable@xxxxxxxxxxxxxxx > > Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver") > > Signed-off-by: Dragan Simic <dsimic@xxxxxxxxxxx> > > Just checking, could this patch be accepted, please? Yes, sorry for the delay. Here's my Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> Steve, any objection? > The Lima > counterpart > has already been accepted. [6] > > The approach in this patch is far from perfect, but it's still fine > until > there's a better solution, such as harddeps. I'll continue my research > about the possibility for introducing harddeps, which would hopefully > replace quite a few instances of the softdep (ab)use that already extend > rather far. For example, have a look at the commit d5178578bcd4 (btrfs: > directly call into crypto framework for checksumming) [7] and the lines > containing MODULE_SOFTDEP() at the very end of fs/btrfs/super.c. [8] > > If a filesystem driver can rely on the (ab)use of softdeps, which may be > fragile or seen as a bit wrong, I think we can follow the same approach, > at least until a better solution is available. > > [6] > https://cgit.freedesktop.org/drm/drm-misc/commit/?id=0c94f58cef319ad054fd909b3bf4b7d09c03e11c > [7] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d5178578bcd4 > [8] > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/btrfs/super.c#n2593 > > > --- > > drivers/gpu/drm/panfrost/panfrost_drv.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/drivers/gpu/drm/panfrost/panfrost_drv.c > > b/drivers/gpu/drm/panfrost/panfrost_drv.c > > index ef9f6c0716d5..149737d7a07e 100644 > > --- a/drivers/gpu/drm/panfrost/panfrost_drv.c > > +++ b/drivers/gpu/drm/panfrost/panfrost_drv.c > > @@ -828,3 +828,4 @@ module_platform_driver(panfrost_driver); > > MODULE_AUTHOR("Panfrost Project Developers"); > > MODULE_DESCRIPTION("Panfrost DRM Driver"); > > MODULE_LICENSE("GPL v2"); > > +MODULE_SOFTDEP("pre: governor_simpleondemand");
