Re: [PATCH] drm/lima: Mark simple_ondemand governor as softdep

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Hello Qiang Yu,

On 2024-07-26 08:07, Qiang Yu wrote:
Yeah, I agree weakdep is a better choice here. It solves the confusion
of softdep which the depend module is optional.

Thanks, I'm glad that you agree.

But I prefer using weakdep directly instead of creating an aliasing of
it which has no actual difference.

Just checking, did you have a chance to read what I wrote in my earlier
response on the linux-modules mailing list, [7] which includes a rather
elaborate explanation of the intent behind MODULE_HARDDEP being currently
just a proposed alias for MODULE_WEAKDEP?  It also describes why using
this alias might save use some time and effort in the future.

[7] https://lore.kernel.org/linux-modules/0720a516416a92a8f683053d37ee9481@xxxxxxxxxxx/

On Thu, Jul 25, 2024 at 4:21 PM Dragan Simic <dsimic@xxxxxxxxxxx> wrote:

Hello Qiang,

On 2024-06-26 08:49, Dragan Simic wrote:
> On 2024-06-26 03:11, Qiang Yu wrote:
>> On Wed, Jun 26, 2024 at 2:15 AM Dragan Simic <dsimic@xxxxxxxxxxx>
>> wrote:
>>> Just checking, any further thoughts about this patch?
>>>
>> I'm OK with this as a temp workaround because it's simple and do no
>> harm
>> even it's not perfect. If no other better suggestion for short term,
>> I'll submit
>> this at weekend.
>
> Thanks.  Just as you described it, it's 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 adding harddeps, which would
> hopefully
> replace quite a few instances of the softdep (ab)use.

Another option has become available for expressing additional module
dependencies, weakdeps. [1][2]  Long story short, weakdeps are similar
to softdeps, in the sense of telling the initial ramdisk utilities to
include additional kernel modules, but weakdeps result in no module
loading being performed by userspace.

Maybe "weak" isn't the best possible word choice (arguably, "soft" also wasn't the best word choice), but weakdeps should be a better choice for use with Lima and governor_simpleondemand, because weakdeps provide the required information to the utilities used to generate initial ramdisk,
while the actual module loading is left to the kernel.

The recent addition of weakdeps renders the previously mentioned
harddeps
obsolete, because weakdeps actually do what we need. Obviously, "weak"
doesn't go along very well with the actual nature of the dependency
between
Lima and governor_simpleondemand, but it's pretty much just the somewhat
unfortunate word choice.

The support for weakdeps has been already added to the kmod [3][4] and
Dracut [5] userspace utilities. I'll hopefully add support for weakdeps
to mkinitcpio [6] rather soon.

Maybe we could actually add MODULE_HARDDEP() as some kind of syntactic
sugar, which would currently be an alias for MODULE_WEAKDEP(), so the
actual hard module dependencies could be expressed properly, and
possibly
handled differently in the future, with no need to go back and track all
such instances of hard module dependencies.

With all this in mind, here's what I'm going to do:

1) Submit a patch that adds MODULE_HARDDEP() as syntactic sugar
2) Implement support for weakdeps in Arch Linux's mkinitcpio [6]
3) Depending on what kind of feedback the MODULE_HARDDEP() patch
receives,
I'll submit follow-up patches for Lima and Panfrost, which will swap
    uses of MODULE_SOFTDEP() with MODULE_HARDDEP() or MODULE_WEAKDEP()

Looking forward to your thoughts.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/linux/module.h?id=61842868de13aa7fd7391c626e889f4d6f1450bf [2] https://lore.kernel.org/linux-kernel/20240724102349.430078-1-jtornosm@xxxxxxxxxx/T/#u [3] https://github.com/kmod-project/kmod/commit/05828b4a6e9327a63ef94df544a042b5e9ce4fe7 [4] https://github.com/kmod-project/kmod/commit/d06712b51404061eef92cb275b8303814fca86ec [5] https://github.com/dracut-ng/dracut-ng/commit/8517a6be5e20f4a6d87e55fce35ee3e29e2a1150
[6] https://gitlab.archlinux.org/archlinux/mkinitcpio/mkinitcpio



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