Messages in this thread | | | Date | Wed, 5 Oct 2016 01:28:04 +0200 | From | "Luis R. Rodriguez" <> | Subject | Re: [RFC] fs: add userspace critical mounts event support |
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On Fri, Sep 23, 2016 at 07:51:41PM -0700, Herbert, Marc wrote: > On 06/09/2016 16:04, Luis R. Rodriguez wrote: > > They claim that without it there is the race between /lib/firmware > > being ready and driver asking for the firmware. > > Hope it's understood by now. > > > I was told there were quite a bit of out-of-tree hacks to address > > this without using the usermode helper, > > There are: > https://chromium-review.googlesource.com/#/c/354089/ > wait until SYSTEM_RUNNING before loading DMC firmware.
Jeesh. Good thing its not merged yet upstream, but indeed I can understand why out of tree kernels are picking these sorts of solutions up in the meantime.
> > the goal of this patch was to create the discussion needed to a > > proper resolution to this. > > Sincere thanks. > > >>> On Tue 06 Sep 11:32 PDT 2016, Linus Torvalds wrote: > >>> > >>>> On Tue, Sep 6, 2016 at 10:46 AM, Bjorn Andersson > >>>> Nobody has actually answered the "why don't we just tie the > >>>> firmware and module together" question. > >>> > >>> The answer to this depends on the details of the suggestion; but > >>> generally there's a much stronger bond between the kernel and the > >>> driver than between the driver and the firmware in my cases. > > Indeed. > > The i915 DMC firmware is an interesting example. First of all it’s > _optional_! It’s critical for battery-powered systems but the i915 > driver works without it.
You obviously may want to upgrade firmware too, and a driver may want to provide support for a series of old and new firmware.
An alternative idea hinted to me recently was a new system call for drivers that need firmware early, so we'd have system call deal with loading *both* the module and firmware -- but indeed optional firmware is one possible issue that throws a wrench into this. We can surely add a flags option but not yet sure if that alone would suffice for most of our needs. You may need code to generate the firmware name dynamically as well, so a system call would only be useful for a few cases where firmware requirement information can be inferred by userspace by just looking at the module object.
> Dan wrote: > > Plus all gpu drivers which need firmware. And yes we must load them > > at probe because people are generally pissed when they boot their > > machine and the screen goes black.
Thanks for the clarification BTW.
> > On top of that a lot of people > > want their gpu drivers to be built-in, but can't ship the firmware > > blobs in the kernel image because gpl. Yep, there's a bit a > > contradiction there ... > > Eppur si muove: > 1) As Dan just wrote, users expect the screen to light up as soon as they > press the power button so the i915 driver is built-in > 2) ... yet they’ll never notice the nanojoules of battery loss caused > by the DMC firmware being on a filesystem and loaded a tiny bit later. > > SoCs and platforms have become some new kind of distributed systems > where other processors run their own, specific software/OS/firmware. > From this perspective the kernel plays a role similar to a boot server; > and choke point. Granted: booting various and heterogeneous > distributed systems doesn’t look like a simple problem to solve > generically. Yet at the moment the kernel doesn’t help by not > even supporting something as basic as being told when the files it’s > (unfortunately) in charge to deploy to other nodes become available and > ready to deploy.
When you consider the problem more from a directed acyclic graph point of view you soon realize the issue is really about the *need* for certain files upon driver load and the lack of of semantics for a deterministic assurance that when we look for files its a valid hunt. What you describe in terms of SoCs is just that the complexity of the DAG increases considerably.
> It can’t be assumed that the driver and the firmware are two parts of > the same software piece whereas they actually run on two different > processors, are most likely developed and validated by completely > different teams and released on different lifecycles. Especially in > the Linux case. > > I hope this distributed systems analogy captures the essence of the > examples and rationales detailed elsewhere in this thread.
You also need to upgrade firmware, and users should be able to opt-in for firmware, and pick any firmware, or roll back to older versions as they see fit.
Luis
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