On Mon, 19 Jan 2004, David Brownell wrote:
Maybe smarter per-port power switching would make bus power surges less of an issue ... right now the hub driver always turns on all ports at once, which probably asks for out-of-spec surges when a bus-powered hub is first turned on, and it's got several devices already connected to it.
I wanted to ask about that. How long should we wait between turning on power to different ports? There's a minimum delay before the port is usable, but that's not the same thing.
The USB 2.0 spec might have some advice there.
By "smarter" I meant something like:
in hub_probe()
- for each port on the hub:
* power it up
* if there's no device there, continue next port
* debounce and let power stabilize
* hub_port_init()
* add device to a new device queue in khubd (later)
- for each device in the new device queue
* usb_new_device() to configureAnd eventually, the config selection code should be noticing cases like "hub can't supply that much power", and flagging that error (syslogging, blinking hub led, etc).
Wouldn't that "khubd (later)" queue work out well in the "morphs" path through usb_reset_device()? Though maybe registering the device in sysfs should be taken out of usb_new_device().
- Dave
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