[Angstrom-devel] usb MaxPower issue

[Marcin Juszkiewicz]

Dnia środa, 9 stycznia 2008, Paul Sokolovsky napisał:

> |>>> insufficient bus power on my C1000, 2.6.23 kernel. lsusb -v says
> |>>> it needs 250 mA MaxPower. Apart from the hardware limitation it

> |>> C1000/3x00 is able to provide 150mA only and any device which wants

> > |   Rather, it's a bug in mainline kernel which they refuse to fix.
> > | Someone, please pull in patch ;-).

You are free to add patch and build own kernel. You can even remove 
power_budget setting from arch/arm/mach-pxa/spitz.c so it will announce 
500mA always. But when your USB port will get fried or device will work 
in random way then do not blame us for it. Power budget setting was added 
to make usage of USB Host in Zaurus devices safe.

Sharp did lot of things wrong in Zaurus hardware - USB Host is one of them 
(other example is power management in c7x0 - with low battery we need to 
limit backlight otherwise CPU voltage can go too low to operate).

> > And risk blowing up your USB controller? You need an Ampere meter to
> > confirm that it always stays below 150mA before trying to patch a
> > kernel for that device, let alone make it global to the usb bus. From
> > what I hear the zaurus lacks overcurrent protection in hardware, so a
> > sysfs switch will most likely result in broken hardware.

>   One can only wonder how it all (I don't mean Zaurus, though I didn't
> hear anything about it either) worked before they added such a check
> in .20-something ;-). But indeed, a patch would add an obscure module
> param to disable the check, not something else...

Only C1000/C3x00 devices use that functionality (checked in 2.6.24-rc7).

Why it worked before? Many devices require less power then they announce 
to USB Host. Remember that USB devices are targetted into PC users not 
palmtop. And nearly all PC devices gives 500mA on at least one port...

-- 
JID: hrw-jabber.org
OpenEmbedded developer/consultant

          It's better to keep your mouth shut and appear stupid,
          than to open it and remove all doubt.