linux-kernel - Re: [PATCH v8 2/7] usb: mux: add generic code for dual role port mux

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Message-ID: <20160527080027.GE22411@kuha.fi.intel.com>
Date:	Fri, 27 May 2016 11:00:27 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Lu Baolu <baolu.lu@...ux.intel.com>
Cc:	felipe.balbi@...ux.intel.com,
	Mathias Nyman <mathias.nyman@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Lee Jones <lee.jones@...aro.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/7] usb: mux: add generic code for dual role port mux

On Thu, May 26, 2016 at 09:03:11AM +0800, Lu Baolu wrote:
> Hi Heikki,
> 
> On 05/25/2016 07:06 PM, Heikki Krogerus wrote:
> > Hi Baolu,
> >
> > Sorry to comment this so late, but we got hardware that needs to
> > configure the mux in OS, and I noticed some problem.
> 
> Comments are always welcome. :-)
> 
> > We are missing
> > means to bind a port to the correct mux on multiport systems. That we
> > need to solve later in any case, but there is an other issue related
> > to the fact that the notifiers now have to be extcon devices. It's
> > related, as extcon offers no means to solve the multiport issue, but
> > in any case..
> >
> >> +struct portmux_dev *portmux_register(struct portmux_desc *desc)
> >> +{
> >> +	static atomic_t portmux_no = ATOMIC_INIT(-1);
> >> +	struct portmux_dev *pdev;
> >> +	struct extcon_dev *edev = NULL;
> >> +	struct device *dev;
> >> +	int ret;
> >> +
> >> +	/* parameter sanity check */
> >> +	if (!desc || !desc->name || !desc->ops || !desc->dev ||
> >> +	    !desc->ops->cable_set_cb || !desc->ops->cable_unset_cb)
> >> +		return ERR_PTR(-EINVAL);
> >> +
> >> +	dev = desc->dev;
> >> +
> >> +	if (desc->extcon_name) {
> >> +		edev = extcon_get_extcon_dev(desc->extcon_name);
> >> +		if (IS_ERR_OR_NULL(edev))
> >> +			return ERR_PTR(-EPROBE_DEFER);
> >> +	}
> >> +
> >> +	pdev = kzalloc(sizeof(*pdev), GFP_KERNEL);
> >> +	if (!pdev)
> >> +		return ERR_PTR(-ENOMEM);
> >> +
> >> +	pdev->desc = desc;
> >> +	pdev->edev = edev;
> >> +	pdev->nb.notifier_call = usb_mux_notifier;
> >> +	mutex_init(&pdev->mux_mutex);
> >> +
> >> +	pdev->dev.parent = dev;
> >> +	dev_set_name(&pdev->dev, "portmux.%lu",
> >> +		     (unsigned long)atomic_inc_return(&portmux_no));
> >> +	pdev->dev.groups = portmux_group;
> >> +	ret = device_register(&pdev->dev);
> >> +	if (ret)
> >> +		goto cleanup_mem;
> >> +
> >> +	dev_set_drvdata(&pdev->dev, pdev);
> >> +
> >> +	if (edev) {
> >> +		ret = extcon_register_notifier(edev, EXTCON_USB_HOST,
> >> +					       &pdev->nb);
> >> +		if (ret < 0) {
> >> +			dev_err(dev, "failed to register extcon notifier\n");
> >> +			goto cleanup_dev;
> >> +		}
> >> +	}
> > So I don't actually think this is correct approach. We are forcing the
> > notifying drivers, on top of depending on this framework, depend on
> > extcon too, and that simply is too much. I don't think a USB PHY or
> > charger detection driver should be forced to generate an extcon device
> > just to satisfy the mux in general.
> 
> Fair enough.
> 
> >
> > Instead IMO, this framework should provide an API also for the
> > notifiers. The drivers that do the notification should not need to
> > depend on extcon at all. Instead they should be able to just request
> > an optional handle to a portmux, and use it with the function that you
> > already provide (usb_mux_change_state(), which of course needs to be
> > exported). That would make it much easier for us to make problems like
> > figuring out the correct mux for the correct port a problem for the
> > framework and not the drivers.
> >
> > extcon does not really add any value here, but it does complicate
> > things a lot. We are even exposing new sysfs attributes to control the
> > mux, complete separate from extcon.
> 
> I agree with you that we should move extcon out of the framework.
> 
> In order to support multiport systems, I have below proposal.
> 
> Currently, we have below interfaces.
> 
> struct portmux_dev *portmux_register(struct portmux_desc *desc);
> void portmux_unregister(struct portmux_dev *pdev);
> 
> I will add below ones.
> 
> struct portmux_dev *portmux_lookup_by_name(char *name);
> int portmux_switch(struct portmux_dev *pdev, enum port_role);
> 
> The normal usage mode is
> 1) the mux device is registered as soon as a mux is detected with
>     portmux_register();
> 2) In components like USB PHY or changer drivers, the mux could
>     be retrieved with portmux_lookup_by_name() and controlled via
>     portmux_switch().
> 
> Is this helpful?

It works for me, and we can improve it later if needed.


Thanks,

-- 
heikki