[PATCH 1/3] usb: misc: generic_onboard_hub: add generic onboard USB HUB driver

[l.stach@pengutronix.de (Lucas Stach)]

Am Mittwoch, den 09.12.2015, 17:00 +0800 schrieb Peter Chen:
> On Wed, Dec 09, 2015 at 09:57:40AM +0100, Lucas Stach wrote:
> > Am Mittwoch, den 09.12.2015, 16:50 +0800 schrieb Peter Chen:
> > > On Tue, Dec 08, 2015 at 08:36:00AM -0700, Mathieu Poirier wrote:
> > > > On 7 December 2015 at 18:37, Peter Chen <peter.chen@freescale.com> wrote:
> > > > > +
> > > > > +       if (dev->of_node) {
> > > > > +               struct device_node *node = dev->of_node;
> > > > > +
> > > > > +               hub_data->clk = devm_clk_get(dev, "external_clk");
> > > > > +               if (IS_ERR(hub_data->clk)) {
> > > > > +                       dev_dbg(dev, "Can't get external clock: %ld\n",
> > > > > +                                       PTR_ERR(hub_data->clk));
> > > > > +               }
> > > > 
> > > > Is the intended behaviour to keep going here event when there is an
> > > > error?  Can the "hub_data" really work without a clock?
> > > 
> > > Yes, some HUB may work with fixed 24M OSC at the board, but they need to
> > > reset through external IO, so the clock is not need at this case, but
> > > reset pin is mandatory.
> > > 
> > If the hub always requires a clock it must not be optional. If you have
> > a fixed 24MHz clock on board add this to the DT as a fixed-clock and use
> > it as an input to the hub.
> > 
> 
> This fixed 24MHz clock may from a fixed crystal on board, it is always
> on, no software need to control it, imx51-bbg board is an example.
> 
And that's wh it is a fixed-clock. Please look it up in the DT binding
documentation.
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