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Re: PXA27x UDC Power

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On Wednesday 28 November 2007, Thomas Giesel wrote:
> 
> How about adding a module parameter for g_ether which describes
> the power consumption? After adding this patch this even could
> go to the kernel main line, because it is not device specific
> but can be configured at runtime.

That would work.  I don't like relying so much on module parameters
for things that should never change over the lifetime of a product,
but I'd not deny that can be made to work.


> Do you have a reason to support more than one configuration?

Avoiding unnecessary restrictions on the device.


> (e.g. you could *always* ask for 500 mA when your device is
> connected to the host, which means that it mustn't be connected
> to a unpowered hub - which is acceptable for this kind of devices, imho)       

... *that* kind of unneccessary restriction.  It's not like the
board requires 500 mA to operate ... it's only that when it gets
only 100 mA it may not be able to recharge as quickly.


> btw: I'll try to do something very similar in the next days.
> Did you use these: http://wiki.enneenne.com/index.php/PXA27x_UDC ?

I saw an earlier version.  I'm still hoping someone submits
a decent version of that driver ... one that doesn't require
changes to the whole gadget stack to cope with Intel's odd
notions about configuration management.

- Dave

> Did you have to add more changes? I got the mass storage device
> up and running (PXA27x + Win2k host), but the CDC Ethernet didn't
> work with a MCCI driver at the first try.    
> 
> Thomas
> 
> linux-usb-devel-bounces@xxxxxxxxxxxxxxxxxxxxx wrote:
> > On Wednesday 28 November 2007, Justin Clacherty wrote:
> >> David Brownell wrote:
> >>> Right now the only way to do that is to modify your configuration
> >>> descriptors. 
> >>> 
> >> I expected that would be the case but I didn't like the idea of
> >> putting machine specific configurations in ether.c.  Is this a
> >> problem with the gadget subsystem in general or just the PXA?
> > 
> > I'm not sure I see it as a problem.  At that level, power
> > management is highly product-specific -- if you want anything
> > other than very generic behavior.  Part of the reason you
> > want source code is specifically so you can customize stuff
> > like that.
> > 
> > Plus, didn't you say you wanted multiple configurations ... a
> > standard one, and a higher power one for battery recharging?
> > 
> > 
> >> I've seen that there is a call to vbus_draw once the device is
> >> configured and I can change the current draw to 500mA here but how
> >> will I know if the device I'm attached to can supply the required
> >> 500mA? 
> > 
> > You get connected to a host ... the host chooses a configuration
> > it can support.  The ability to supply 500mA is an attribute
> > of the port the gadget is hooked up to.  For example, unpowered
> > hubs provide only 100 mA per port, but most powered ones can
> > supply 500mA (or even more).
> > 
> > - Dave
> > 
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