Re: [PATCH 1/5] dt/bindings: Add binding for the DA8xx MUSB driver

On Fri, Feb 12, 2016 at 11:24 AM, Petr Kulhavy [off-list ref] wrote:

On 12.02.2016 17:21, Rob Herring wrote:

quoted

On Thu, Feb 11, 2016 at 12:01:06PM +0100, Petr Kulhavy wrote:

quoted

+ - mentor,power : Specifies the maximum current in milliamperes the
controller can
+     supply in host mode.

Still a no for me. Looks like this just sets hcd->power_budget. This
property may not be a regulator, but ultimately the value depends on
some regulator supplying Vbus. Also, given this has nothing to do with
MUSB h/w, however this is described should be generic.

I understand your point that the description should be generic.
However the USB 2.0 specification does not define any relation between the
bMaxPower provided by the device and the actual power control.
As far as I understand the value just serves the purpose to raise a flag to
the user if the attached device would draw too much power, and not to enable
it at all.

That won't really work given devices lie. My bus powered USB disk
enclosure reports something like 10mA. That's pretty good considering
I have a 5W drive in it.

Further, the value used by the protocol is not necessarily related to the
real current that can be supported. The maximum current supported by the
protocol is 510mA.

For instance on my development board the real maximum current is limited
only by the mains power-supply used.
So it cannot even be modelled in the DT as a regulator because the
power-supply is not part of the HW and
everybody can take a different one.

Not part of which h/w? Different for everyone is exactly why Vbus
supply should be described in DT.

So defining a regulator just to store this arbitrary USB 2.0 value is a bit
overkill for me.

If it is just arbitrary, then put it into the driver. I would do 500mA
and be done with it. I'd guess there is nothing real behind the
current default of 250mA.

Rob
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