[PATCH 1/3] usb: core: add power sequence for USB devices

[hzpeterchen@gmail.com (Peter Chen)]

On Thu, Mar 03, 2016 at 01:31:56PM -0500, Alan Stern wrote:
> On Thu, 3 Mar 2016, Peter Chen wrote:
> 
> > Some hard-wired USB devices need to do power sequence to let the
> > device work normally, the typical power sequence like: enable USB
> > PHY clock, toggle reset pin, etc. But current Linux USB driver
> > lacks of such code to do it, it may cause some hard-wired USB devices
> > works abnormal or can't be recognized by controller at all.
> > 
> > In this patch, it will do power on sequence at hub's probe for all
> > devices under this hub (includes root hub) if this device is described
> > at dts and there is a phandle "usb-pwrseq" for it. At hub_disconnect,
> > it will do power off sequence.
> > 
> > Signed-off-by: Peter Chen <peter.chen@nxp.com>
> 
> 
> > +static int hub_of_pwrseq(struct usb_device *hdev, bool on)
> > +{
> > +	struct device *parent;
> > +	struct device_node *node;
> > +	int ret = 0;
> > +
> > +	if (hdev->parent)
> > +		parent = &hdev->dev;
> > +	else
> > +		parent = bus_to_hcd(hdev->bus)->self.controller;
> > +
> > +	for_each_child_of_node(parent->of_node, node) {
> > +		ret = on ? usb_child_pwrseq_on(node)
> > +			: usb_child_pwrseq_off(node);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> 
> If you get a failure, do you want to leave the power to all the
> preceding devices turned on?  It seems to me you should either turn all 
> of them back off, or else continue trying to turn on power for the 
> remaining children.
> 

Thanks, I will show error message for that device, and continue to turn
on power for the remaining children.

-- 

Best Regards,
Peter Chen