On 03/07/2024 13:42, Dragan Simic 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> Reviewed-by: Steven Price <steven.price@xxxxxxx> > > Just checking, could this patch be accepted, please? The Lima counterpart > has already been accepted. [6] Thanks for the prod - I have to admit I saw there was discussion about the Lima patch and so just put this on my list to look again later after the discussion had reached a conclusion. > 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] I agree - it's not perfect, but it's the best we have for now. I hope sometime we'll have a cleaner solution to express dependencies like this (good luck! ;) ). Thanks, Steve > 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");
