Re: [PATCH RFC] USB: Add HCD fastboot

Alan Stern
2008-08-06T20:26:53Z

On Wed, 6 Aug 2008, Simon Arlott wrote:

> No, by adding a 5 second delay you're intending for the device driver initcalls
> to complete within that 5 seconds. If they take too long then the last one
> blocks everything (I realise that's ridiculous, these initcalls take <1ms when
> there are no devices yet). The best way to do is to make the driver initcalls
> before the host ones, like you suggested.

Doing the HCD initcalls last certainly ought to work.

> > "it'll still have to wait..." If by "it" you mean the initcall
> > thread, you're wrong. If by "it" you mean the user, you still aren't
> > necessarily correct; the user can do plenty of other things while
> > waiting for USB devices to initialize.
>
> Assuming userspace doesn't wait for all devices to settle and appear in /dev etc.
> before continuing.

Whatever that involves... /dev never truly settles; it's always
possible to plug in a new device or remove an old one.

> > I suppose you could make the hub_thread delay time a module parameter
> > for usbcore, defaulting to 0. Then it could be set by just the people
> > who want to use it -- many (most?) people keep their drivers in
> > modules, and it wouldn't do them any good.
>
> It really needs to have hcd initcalls done very early so that device init

Please stop using the word "it" with no antecedent! Do you mean "we"?

> has the rest of the (kernel and userspace) boot process to complete in the
> background. This is negated by having device drivers initialised immediately
> afterwards. Re-ordering initcalls and doing more of the init process
> asynchronously is likely to expose bugs and cause inconsistent device order
> on some systems, so if the makefile mess could be reduced then it can be a
> Kconfig option.

So what exactly do you recommend?

> How many people have *all* their USB components (hcd, drivers) as modules?

All the major distributions do, as far as I know. (I haven't actually
checked them all to be certain.)

> What do they do with their USB keyboards in the period between init and module
> load?

Probably nothing. What do you do on your keyboard while waiting for
system initialization to complete?

> If even one device driver and the hcd is compiled in, they'd need to
> wait for every USB device to finish init before the usbhid probe could complete.

What if usbhid is the one device driver that is compiled in? :-)

Alan Stern