Messages in this thread | | | Date | Wed, 06 Aug 2008 22:49:28 +0100 | From | Simon Arlott <> | Subject | Re: [PATCH RFC] USB: Add HCD fastboot |
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On 06/08/08 21:26, Alan Stern wrote: > 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.
Right - so then all that's needed is to move usb/ before most other things that take a while to init, and it has some time to initialise usb devices in the background.
>> > "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.
Yes... I'm not sure how that part would work.
>> > 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"?
Yes. I'll try to avoid doing that.
>> 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?
I'm not an expert on what can be done with the Makefile process, perhaps there's an easier way to move things around based on a config option. If host init is moved before device init for everyone, wouldn't there be too many side effects?
I've not tried to use usb-storage as root but presumably that works. If that already uses a hack of making the kernel wait X seconds before trying to mount root then it'll still work.
>> 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?
Lack of a keyboard makes it impossible to do anything if the module fails to load... as I understand it when the HCD init runs, any BIOS emulation stops? Although if HCD is a module too...
>> 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? :-)
That was the situation I was thinking of - surely that would be compiled in if the HCDs were?
-- Simon Arlott
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