Re: [PATCH 8/9 v2] usb: usb251xb: Add max power/current dts property support

[Serge Semin <fancer.lancer@gmail.com>]

On Wed, Sep 20, 2017 at 03:52:55PM -0500, Rob Herring <robh@kernel.org> wrote:
> On Sat, Sep 16, 2017 at 01:42:19PM +0300, Serge Semin wrote:
> > This parameters may be varied in accordance with hardware specifics.
> > So lets add the corresponding settings to the usb251x driver dts
> > specification.
> > 
> > Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
> > ---
> >  Documentation/devicetree/bindings/usb/usb251xb.txt   |  6 ++++++
> >  drivers/usb/misc/usb251xb.c                          | 20 ++++++++++++++++----
> >  2 files changed, 22 insertions(+), 4 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/usb/usb251xb.txt b/Documentation/devicetree/bindings/usb/usb251xb.txt
> > index 3d84626d3..dd59a32e7 100644
> > --- a/Documentation/devicetree/bindings/usb/usb251xb.txt
> > +++ b/Documentation/devicetree/bindings/usb/usb251xb.txt
> > @@ -44,6 +44,12 @@ Optional properties :
> >  	device connected.
> >   - sp-disabled-ports : Specifies the ports which will be self-power disabled
> >   - bp-disabled-ports : Specifies the ports which will be bus-power disabled
> > + - sp-max-{power,current} : Indicates the power/current consumed by hub from
> > +	an upstream port (VBUS) when operation as a self-powered hub. The value
> > +	is given in mA in a 0 - 100 range (default is 1mA).
> > + - bp-max-{power,current} : Indicates the power/current consumed by hub from
> > +	an upstream port (VBUS) when operation as a bus-powered hub. The value
> > +	is given in mA in a 0 - 510 range (default is 100mA).
> 
> These need units as defined in property-units.txt.
> 

Ok.

> Why do you need power and current? Can't you calculate power?
> 

These are different parameters of the device. They got different configuration
registers and descriptions:
max_power* - ... This value also includes the power consumption of a
permanently attached peripheral if the hub is configured as a compound
device, and the embedded peripheral reports 0mA in its descriptors.
max_current* - ... This value does NOT include the power consumption of a
permanently attached peripheral if the hub is configured as a compound
device.

Additionally as you can see, they both are measured in "mA", so it isn't
a real physical power.

> >   - power-on-time-ms : Specifies the time it takes from the time the host
> >  	initiates the power-on sequence to a port until the port has adequate
> >  	power. The value is given in ms in a 0 - 510 range (default is 100ms).