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Date:	Wed, 24 Dec 2014 14:43:27 -0800
From:	David Cohen <david.a.cohen@...ux.intel.com>
To:	Felipe Balbi <balbi@...com>
Cc:	myungjoo.ham@...sung.com, cw00.choi@...sung.com,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	baolu.lu@...ux.intel.com, Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [RFC/PATCH] extcon: otg_gpio: add driver for USB OTG port
 controlled by GPIO(s)

Hi Felipe,

Thanks replying.

On Tue, Dec 23, 2014 at 06:29:04PM -0600, Felipe Balbi wrote:
> Hi,
> 
> On Mon, Dec 22, 2014 at 02:43:37PM -0800, David Cohen wrote:
> > Some platforms have an USB OTG port fully (or partially) controlled by
> > GPIOs:
> > 
> > (1) USB ID is connected directly to GPIO
> > 
> > Optionally:
> > (2) VBUS is enabled by a GPIO (when ID is grounded)
> 
> ok, so a fixed regulator with a GPIO enable pin.

Pretty much yes.

> 
> > (3) Platform has 2 USB controllers connected to same port: one for
> >     device and one for host role. D+/- are switched between phys
> >     by GPIO.
> 
> so you have discrete mux with a GPIO select signal, like below ?
> 
> 
>  .-------.----------------.  .--------.
>  |       |                |  |        |      D+
>  |       |                |  |        |<-------------.
>  |       |                |  |        |              |
>  |       |    USB Host    -->|    P   |              |
>  |       |                |  |    H   |              |
>  |       |                |  |    Y   |    D-        |
>  |       '----------------'  |    0   |<--------.    |
>  |                       |   |        |         |    |
>  |                       |   '--------'      .--------.  D+
>  |                       |                   |        |------>
>  |       SOC        GPIO | ----------------->|        |
>  |                       |                   |   MUX  |
>  |                       |                   |        |------>
>  |                       |   .--------.      '--------'  D-
>  |       .----------------.  |        |   D-  |      |
>  |       |                |  |    P   |<------'      |
>  |       |                |  |    H   |              |
>  |       |                |  |    Y   |              |
>  |       |   USB Device   -->|    1   |              |
>  |       |                |  |        |      D+      |
>  |       |                |  |        |<-------------'
>  |       |                |  |        |
>  '-------'----------------'  '--------'

Nice ASCII pic :)
Yes, that's the case.

> 
> I have been on and off about writing a pinctrl-gpio.c driver which would
> allow us to hide this detail from users. It shouldn't really matter
> which modes are available behind the mux, but we should be able to tell
> the mux to go into mode 0 or mode 1 by toggling its select signal. And
> it shouldn't really matter that we have a GPIO pin. The problem is: I
> don't really know if pinctrl would be able to handle discrete muxes.
> 
> Adding Linus W to ask. Linus, what do you think ? Should we have a
> pinctrl-gpio.c for such cases ? In TI we too have quite a few boards
> which different modes hidden behind discrete muxes.

An input from Linus would fine in this case.

> 
> > As per initial version, this driver has the duty to control whether
> > USB-Host cable is plugged in or not:
> >  - If yes, OTG port is configured for host role
> >  - If no, by standard, the OTG port is configured for device role
> 
> correct, this default-B is mandated by OTG spec anyway.
> 
> > Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> > ---
> > 
> > Hi,
> > 
> > Some Intel Bay Trail boards have an unusual way to handle the USB OTG port:
> >  - The USB ID pin is connected directly to GPIO on SoC
> >  - When in host role, VBUS is provided by enabling a GPIO
> >  - Device and host roles are supported by 2 independent controllers with D+/-
> >    pins from port switched between different phys according a GPIO level.
> > 
> > The ACPI table describes this USB port as a (virtual) device with all the
> > necessary GPIOs. This driver implements support to this virtual device as an
> > extcon class driver. All drivers that depend on the USB OTG port state (USB phy,
> > PMIC, charge detection) will listen to extcon events.
> 
> Right I think you're almost there, but I still think that this needs to
> be a bit broken down. First, we need some generic DRD library under
> drivers/usb/common, and that should be the one listening to extcon cable
> events. But your extcon driver should be doing only that: checking which
> cable was attached, it shouldn't be doing the switch by itself. That
> should be part of the DRD library.
> 
> That DRD library would also be the one enabling the (optional) VBUS
> regulator.
> 
> George Cherian tried to implement a generic DRD library but I think
> there are still too many changes happening on usbcore and udc-core. Most
> of the pieces are already there (usb_del_hcd() and usb_del_gadget_udc()
> know how to properly unload an hcd/udc), but there are details missing,
> no doubt.
> 
> If we can find a way to broadcast (probably not the best term, but
> whatever) a "Hey ID pin was just grounded" message, we can get things
> working.
> 
> That message, btw, shouldn't really depend on extcon-gpio alone because
> other platforms might use non-gpio methods to verify ID pin level. In
> any case, we need to have generic ID_PIN_LOW and ID_PIN_HIGH messages
> that a generic DRD library can listen to and load/unload the correct
> drivers by means of usb_{add,del}_{hcd,gadget_udc}().

IMHO extcon is the correct way to broadcast it, as long as we define a
standard for the cable names. E.g. DRD library could listen to
"USB-HOST" cable state. Then it doesn't matter how ID pin is grounded,
it just matters that whoever is controlling it broadcast via this cable.

> 
> With that in mind, I think you can use extcon-gpio.c for your purposes
> if the other pieces can be fullfilled by regulator and pinctrl.

In my case we have all gpios listed in a single ACPI device. In order to
be backwards compatible with products already on market, we'd need
something like a single mfd to register platform devices for this
smaller pieces (extcon gpio, possible pintrl gpio, maybe vbus as regulator??).

> 
> > diff --git a/drivers/extcon/Makefile b/drivers/extcon/Makefile
> > index 0370b42e5a27..9e81088c6584 100644
> > --- a/drivers/extcon/Makefile
> > +++ b/drivers/extcon/Makefile
> > @@ -12,3 +12,4 @@ obj-$(CONFIG_EXTCON_MAX8997)	+= extcon-max8997.o
> >  obj-$(CONFIG_EXTCON_PALMAS)	+= extcon-palmas.o
> >  obj-$(CONFIG_EXTCON_RT8973A)	+= extcon-rt8973a.o
> >  obj-$(CONFIG_EXTCON_SM5502)	+= extcon-sm5502.o
> > +obj-$(CONFIG_EXTCON_OTG_GPIO) += extcon-otg_gpio.o
> > diff --git a/drivers/extcon/extcon-otg_gpio.c b/drivers/extcon/extcon-otg_gpio.c
> > new file mode 100644
> > index 000000000000..c5ee765a5f4f
> > --- /dev/null
> > +++ b/drivers/extcon/extcon-otg_gpio.c
> > @@ -0,0 +1,200 @@
> > +/*
> > + * Virtual USB OTG Port driver controlled by gpios
> > + *
> > + * Copyright (c) 2014, Intel Corporation.
> > + * Author: David Cohen <david.a.cohen@...ux.intel.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <linux/acpi.h>
> > +#include <linux/extcon.h>
> > +#include <linux/gpio.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/platform_device.h>
> > +
> > +#define DRV_NAME	"usb_otg_port"
> > +
> > +struct vuport {
> > +	struct device *dev;
> > +	struct gpio_desc *gpio_vbus_en;
> > +	struct gpio_desc *gpio_usb_id;
> > +	struct gpio_desc *gpio_usb_mux;
> > +
> > +	struct extcon_dev edev;
> > +};
> > +
> > +static const char *const vuport_extcon_cable[] = {
> > +	[0] = "USB-Host",
> > +	NULL,
> > +};
> > +
> > +/*
> > + * If id == 1, USB port should be set to peripheral
> > + * if id == 0, USB port should be set to host
> > + *
> > + * Peripheral: set USB mux to peripheral and disable VBUS
> > + * Host: set USB mux to host and enable VBUS
> > + */
> > +static void vuport_set_port(struct vuport *vup, int id)
> > +{
> > +	int mux_val = id;
> > +	int vbus_val = !id;
> > +
> > +	if (!IS_ERR(vup->gpio_usb_mux))
> > +		gpiod_direction_output(vup->gpio_usb_mux, mux_val);
> > +
> > +	if (!IS_ERR(vup->gpio_vbus_en))
> > +		gpiod_direction_output(vup->gpio_vbus_en, vbus_val);
> 
> not all SoCs will allow for direction to be set all the time. This can
> be glitchy in some cases. What you want here is to set direction during
> probe and just set value here.

It makes sense, I'll change it.

> 
> > +static void vuport_do_usb_id(struct vuport *vup)
> > +{
> > +	int id = gpiod_get_value(vup->gpio_usb_id);
> > +
> > +	dev_info(vup->dev, "USB PORT ID: %s\n", id ? "PERIPHERAL" : "HOST");
> 
> info ? sounds like debug to me.

Ack.

> 
> > +
> > +	/*
> > +	 * id == 1: PERIPHERAL
> > +	 * id == 0: HOST
> > +	 */
> > +	vuport_set_port(vup, id);
> > +
> > +	/*
> > +	 * id == 0: HOST connected
> > +	 * id == 1: Host disconnected
> > +	 */
> > +	extcon_set_cable_state(&vup->edev, "USB-Host", !id);
> > +}
> > +
> > +static irqreturn_t vuport_thread_isr(int irq, void *priv)
> > +{
> 
> this is unrelated to $subject, but I always consider if we should have a
> generic way to figure out if the interrupt was for rising or falling
> edge, if we knew that, we could avoid reading the GPIO value altogether
> ;-)

Yeah, that would be nice.

> 
> > +	struct vuport *vup = priv;
> > +
> > +	vuport_do_usb_id(vup);
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static irqreturn_t vuport_isr(int irq, void *priv)
> > +{
> > +	return IRQ_WAKE_THREAD;
> > +}
> 
> you don't need this. Set the top half handler to NULL and pass
> IRQF_ONESHOT (which you shoudl already have set anyway).

Ack.

> 
> > +#define VUPORT_GPIO_USB_ID	0
> > +#define VUPORT_GPIO_VBUS_EN	1
> > +#define VUPORT_GPIO_USB_MUX	2
> > +static int vuport_probe(struct platform_device *pdev)
> > +{
> > +	struct device *dev = &pdev->dev;
> > +	struct vuport *vup;
> > +	int ret;
> > +
> > +	vup = devm_kzalloc(dev, sizeof(*vup), GFP_KERNEL);
> > +	if (!vup) {
> > +		dev_err(dev, "cannot allocate private data\n");
> > +		return -ENOMEM;
> > +	}
> > +	vup->dev = dev;
> > +
> > +	vup->gpio_usb_id = devm_gpiod_get_index(dev, "id", VUPORT_GPIO_USB_ID);
> > +	if (IS_ERR(vup->gpio_usb_id)) {
> > +		dev_err(dev, "cannot request USB ID GPIO: ret = %ld\n",
> > +			PTR_ERR(vup->gpio_usb_id));
> > +		return PTR_ERR(vup->gpio_usb_id);
> > +	}
> > +
> > +	ret = gpiod_direction_input(vup->gpio_usb_id);
> > +	if (ret < 0) {
> > +		dev_err(dev, "cannot set input direction to USB ID GPIO: ret = %d\n",
> > +			ret);
> > +		return ret;
> > +	}
> > +
> > +	vup->gpio_vbus_en = devm_gpiod_get_index(dev, "vbus en",
> > +						 VUPORT_GPIO_VBUS_EN);
> > +	if (IS_ERR(vup->gpio_vbus_en))
> > +		dev_info(dev, "cannot request VBUS EN GPIO, skipping it.\n");
> > +
> > +	vup->gpio_usb_mux = devm_gpiod_get_index(dev, "usb mux",
> > +						 VUPORT_GPIO_USB_MUX);
> > +	if (IS_ERR(vup->gpio_usb_mux))
> > +		dev_info(dev, "cannot request USB USB MUX, skipping it.\n");
> > +
> > +	/* register extcon device */
> > +	vup->edev.dev.parent = dev;
> > +	vup->edev.supported_cable = vuport_extcon_cable;
> 
> IIRC, edev should be allocated from now on. Have a look at
> devm_extcon_dev_allocate() and devm_extcon_dev_register().

Thanks, I'll check.

> 
> > +	ret = extcon_dev_register(&vup->edev);
> > +	if (ret < 0) {
> > +		dev_err(dev, "failed to register extcon device: ret = %d\n",
> > +			ret);
> > +		return ret;
> > +	}
> > +
> > +	ret = devm_request_threaded_irq(dev, gpiod_to_irq(vup->gpio_usb_id),
> > +					vuport_isr, vuport_thread_isr,
> > +					IRQF_SHARED | IRQF_TRIGGER_RISING |
> > +					IRQF_TRIGGER_FALLING,
> > +					dev_name(dev), vup);
> > +	if (ret < 0) {
> > +		dev_err(dev, "cannot request IRQ for USB ID GPIO: ret = %d\n",
> > +			ret);
> > +		goto irq_err;
> > +	}
> > +	vuport_do_usb_id(vup);
> > +
> > +	platform_set_drvdata(pdev, vup);
> > +
> > +	dev_info(dev, "driver successfully probed\n");
> 
> this will just make boot noisier, make it dev_dbg() ? Or even
> dev_vdbg() ?

dev_dgb() perhaps.

> 
> > +MODULE_LICENSE("GPL");
> 
> you header on the top of this C file states gpl 2 only, but this says
> GPL 2+.

I'll fix it.

Thanks,

David

> 
> cheers
> 
> -- 
> balbi


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