On 25/07/2024 12:37, Dragan Simic wrote: > Panfrost and Lima DRM drivers use devfreq to perform DVFS, which is supported > on the associated platforms, while using simple_ondemand devfreq governor by > default. This makes the simple_ondemand module a hard dependency for both > Panfrost and Lima, because the presence of the simple_ondemand module in an > initial ramdisk allows the initialization of Panfrost or Lima to succeed. > This is currently expressed using MODULE_SOFTDEP. [1][2] Please see commits > 80f4e62730a9 ("drm/panfrost: Mark simple_ondemand governor as softdep") and > 0c94f58cef31 ("drm/lima: Mark simple_ondemand governor as softdep") for > additional background information. > > With the addition of MODULE_WEAKDEP in commit 61842868de13 ("module: create > weak dependecies"), the dependency between Panfrost/Lima and simple_ondemand > can be expressed in a much better way as a weakdep, because that provides > the required dependency information to the utilities that generate initial > ramdisks, but leaves the actual loading of the required kernel module(s) to > the kernel. However, being able to actually express this as a hard module > dependency would still be beneficial. > > With all this in mind, let's add MODULE_HARDDEP as some kind of syntactic > sugar, currently implemented as an alias for MODULE_WEAKDEP, so the actual > hard module dependencies can be expressed properly, and possibly handled > differently in the future, avoiding the need to go back, track and churn > all such instances of hard module dependencies. The first consumers of > MODULE_HARDDEP will be the Panfrost and Lima DRM drivers, but the list of > consumers may also grow a bit in the future. > > For example, allowing reduction of the initial ramdisk size is a possible > future difference between handling the MODULE_WEAKDEP and MODULE_HARDDEP > dependencies. When the size of the initial ramdisk is limited, the utilities > that generate initial ramdisks can use the distinction between the weakdeps > and the harddeps to safely omit some of the weakdep modules from the created > initial ramdisks, and to keep all harddep modules. > > Due to the nature of MODULE_WEAKDEP, the above-described example will also > require some additional device-specific information to be made available to > the utilities that create initial ramdisks, so they can actually know which > weakdep modules can be safely pruned for a particular device, but the > distinction between the harddeps and the weakdeps opens up a path towards > using such additional "pruning information" in a more robust way, by ensuring > that the absolutely required harddep modules aren't pruned away. > > [1] https://lore.kernel.org/dri-devel/4e1e00422a14db4e2a80870afb704405da16fd1b.1718655077.git.dsimic@xxxxxxxxxxx/T/#u > [2] https://lore.kernel.org/dri-devel/fdaf2e41bb6a0c5118ff9cc21f4f62583208d885.1718655070.git.dsimic@xxxxxxxxxxx/T/#u > > Cc: Steven Price <steven.price@xxxxxxx> > Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> > Cc: Qiang Yu <yuq825@xxxxxxxxx> > Signed-off-by: Dragan Simic <dsimic@xxxxxxxxxxx> Thanks Dragan, while there's obviously a bunch more work to hook this up appropriately, this at least lets drivers signal the actual requirement. Reviewed-by: Steven Price <steven.price@xxxxxxx> Steve > --- > include/linux/module.h | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/include/linux/module.h b/include/linux/module.h > index 88ecc5e9f523..40e5762847a9 100644 > --- a/include/linux/module.h > +++ b/include/linux/module.h > @@ -179,6 +179,14 @@ extern void cleanup_module(void); > */ > #define MODULE_WEAKDEP(_weakdep) MODULE_INFO(weakdep, _weakdep) > > +/* > + * Hard module dependencies. Currently handled the same as weak > + * module dependencies, but intended to mark hard dependencies > + * as such for possible different handling in the future. > + * Example: MODULE_HARDDEP("module-foo") > + */ > +#define MODULE_HARDDEP(_harddep) MODULE_WEAKDEP(_harddep) > + > /* > * MODULE_FILE is used for generating modules.builtin > * So, make it no-op when this is being built as a module