Date:	Wed, 29 Oct 2014 11:21:05 -0500
From:	Benoit Parrot <bparrot@...com>
To:	Alexandre Courbot <gnurou@...il.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Pantelis Antoniou <panto@...oniou-consulting.com>,
	Jiri Prchal <jiri.prchal@...ignal.cz>
Subject: Re: [RFC Patch] gpio: add GPIO hogging mechanism

Alexandre,

Thanks for the feedback.

Alexandre Courbot <gnurou@...il.com> wrote on Wed [2014-Oct-29 16:09:59 +0900]:
> Sorry for the delay in reviewing. Adding Jiri and Pantelis who might
> want to extend over this patch and thus will likely have interesting
> comments to make.
> 
> On Wed, Oct 22, 2014 at 5:09 AM, Benoit Parrot <bparrot@...com> wrote:
> > Based on Boris Brezillion work this is a reworked patch
> > of his initial GPIO hogging mechanism.
> > This patch provides a way to initally configure specific GPIO
> > when the gpio controller is probe.
> 
> Typo nit: s/probe/probed
Will fix.

> 
> >
> > The actual DT scanning to collect the GPIO specific data is performed
> > as part of the gpiochip_add().
> >
> > The purpose of this is to allows specific GPIOs to be configured
> > without any driver specific code.
> > This particularly usueful because board design are getting
> 
> s/suseful/useful
> 
> > increassingly complex and given SoC pins can now have upward
> 
> s/increassingly/increasingly

Will fix.

> 
> > of 10 mux values a lot of connections are now dependent on
> > external IO muxes to switch various modes and combination.
> >
> > Specific drivers should not necessarily need to be aware of
> > what accounts to a specific board implementation. This board level
> > "description" should be best kept as part of the dts file.
> >
> > Signed-off-by: Benoit Parrot <bparrot@...com>
> > ---
> >  Documentation/devicetree/bindings/gpio/gpio.txt | 33 +++++++++
> >  drivers/gpio/gpiolib-of.c                       | 99 +++++++++++++++++++++++++
> >  drivers/gpio/gpiolib.c                          | 81 ++++++++++++++++++++
> >  include/linux/of_gpio.h                         | 11 +++
> >  4 files changed, 224 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt
> > index 3fb8f53..a9700d8 100644
> > --- a/Documentation/devicetree/bindings/gpio/gpio.txt
> > +++ b/Documentation/devicetree/bindings/gpio/gpio.txt
> 
> Note: changes to DT bindings documentation should generally come as a
> separate patch.
Ok.

> 
> > @@ -103,6 +103,26 @@ Every GPIO controller node must contain both an empty "gpio-controller"
> >  property, and a #gpio-cells integer property, which indicates the number of
> >  cells in a gpio-specifier.
> >
> > +It might contain GPIO hog definitions. GPIO hogging is a mechanism providing
> > +automatic GPIO request and configuration as part of the gpio-controller's
> > +driver probe function.
> > +
> > +Each GPIO hog definition is represented as a child node of the GPIO controller.
> > +Required properties:
> > +- gpios: store the gpio information (id, flags, ...). Shall contain the
> > +  number of cells specified in its parent node (GPIO controller node).
> 
> If would be nice to be able to specify several GPIO references to that
> they can be all set to the same configuration in one row instead of
> requiring one node each.
> 
> > +- input: a property specifying to set the GPIO direction as input.
> > +- output-high: a property specifying to set the GPIO direction to output with
> > +  the value high.
> > +- output-low: a property specifying to set the GPIO direction to output with
> > +  the value low.
> 
> Wouldn't a "direction" property taking one of the values "input",
> "output-low" or "output-high" be easier to parse and generally
> clearer?

I guess here you mean something like this:
	...
	line_y: line_y {
		gpios = <15 0>;
		direction = <output-low>;
	};

Not sure about easier to parse, but it would be clearer.

> 
> > +
> > +Optional properties:
> > +- line-name: the GPIO label name. If not present the node name is used.
> 
> I guess we also could use this for naming the GPIO during its export
> if we decide to allow this in a near-future patch.
> 
Right.

> > +
> > +A GPIO controller can request GPIO hogs using the "gpio-hogs" property, which
> > +encodes a list of requested GPIO hogs.
> > +
> >  Example of two SOC GPIO banks defined as gpio-controller nodes:
> >
> >         qe_pio_a: gpio-controller@...0 {
> > @@ -110,6 +130,19 @@ Example of two SOC GPIO banks defined as gpio-controller nodes:
> >                 reg = <0x1400 0x18>;
> >                 gpio-controller;
> >                 #gpio-cells = <2>;
> > +               gpio-hogs = <&line_b>;
> > +
> > +               /* line_a hog is defined but not enabled in this example*/
> > +               line_a: line_a {
> > +                       gpios = <5 0>;
> > +                       input;
> > +               };
> > +
> > +               line_b: line_b {
> > +                       gpios = <6 0>;
> > +                       output-low;
> > +                       line-name = "foo-bar-gpio";
> > +               };
> 
> I think it might be good to group the hog nodes such as to allow
> complex configurations to be set in one go, à la pinmux:

See below.
> 
>                 gpio-controller;
>                 #gpio-cells = <2>;
> +               gpio-hogs = <&line_b>;
> +
> +               line_a: line_a {
> +                      line_a {
> +                               gpios = <5 0>;
> +                               input;
> +                      };
> +                      line_c {
> +                               gpios = <7 0>;
> +                               inputl
> +                      };
> +               };
> +
> +               line_b: line_b {
> +                       line_b {
> +                               gpios = <6 0>;
> +                               output-low;
> +                               line-name = "foo-bar-gpio";
> +                       };
> +               };
> 
> Here if you want to enable the first configuration you don't need to
> specify all the lines one by one, you just need to select the right
> group.
> 
> I wonder if such usage of child nodes could not interfere with GPIO
> drivers (existing or to be) that need to use child nodes for other
> purposes. Right now there is no way to distinguish a hog node from a
> node that serves another purpose, and that might become a problem in
> the future. Not sure how that should be addressed though - maybe by
> enforcing a "-hog" suffix for the group nodes, e.g. line_a-hog?
> Comments from people more experienced with DT would be nice.

I did consider a "pinmux" flavored format (not sure how hard to parse it would be).
It would allow grouping if nothing else.

	/* Line syntax: line_name <gpio# flags> direction-value [export] */
	gpio-hogs = <&group_y>;

	group_y: group_y {
		gpio-hogs-group = <
			line_x <15 0> output-low
			line_y <16 0> output-high export
			line_z <17 0> input
		>;
	};

> 
> >         };
> >
> >         qe_pio_e: gpio-controller@...0 {
> > diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> > index 604dbe6..7308dfc 100644
> > --- a/drivers/gpio/gpiolib-of.c
> > +++ b/drivers/gpio/gpiolib-of.c
> > @@ -111,6 +111,105 @@ int of_get_named_gpio_flags(struct device_node *np, const char *list_name,
> >  EXPORT_SYMBOL(of_get_named_gpio_flags);
> >
> >  /**
> > + * of_get_gpio_hog() - Get a GPIO hog descriptor, names and flags for GPIO API
> > + * @np:                device node to get GPIO from
> > + * @index:     index of the GPIO
> > + * @name:      GPIO line name
> > + * @flags:     a flags pointer to fill in
> > + *
> > + * Returns GPIO descriptor to use with Linux GPIO API, or one of the errno
> > + * value on the error condition.
> > + */
> > +struct gpio_desc *of_get_gpio_hog(struct device_node *np, int index,
> > +                                 const char **name, unsigned long *flags)
> > +{
> > +       struct device_node *cfg_np, *chip_np;
> > +       enum of_gpio_flags xlate_flags;
> > +       unsigned long req_flags = 0;
> > +       struct gpio_desc *desc;
> > +       struct gg_data gg_data = {
> > +               .flags = &xlate_flags,
> > +               .out_gpio = NULL,
> > +       };
> > +       u32 tmp;
> > +       int i;
> > +       int ret;
> > +
> > +       cfg_np = of_parse_phandle(np, "gpio-hogs", index);
> > +       if (!cfg_np)
> > +               return ERR_PTR(-EINVAL);
> > +
> > +       chip_np = cfg_np->parent;
> > +       if (!chip_np) {
> > +               desc = ERR_PTR(-EINVAL);
> > +               goto out;
> > +       }
> > +
> > +       ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);
> > +       if (ret) {
> > +               desc = ERR_PTR(ret);
> > +               goto out;
> > +       }
> > +
> > +       if (tmp > MAX_PHANDLE_ARGS) {
> > +               desc = ERR_PTR(-EINVAL);
> > +               goto out;
> > +       }
> > +
> > +       gg_data.gpiospec.args_count = tmp;
> > +       gg_data.gpiospec.np = chip_np;
> > +       for (i = 0; i < tmp; i++) {
> > +               ret = of_property_read_u32(cfg_np, "gpios",
> > +                                          &gg_data.gpiospec.args[i]);
> > +               if (ret) {
> > +                       desc = ERR_PTR(ret);
> > +                       goto out;
> > +               }
> > +       }
> > +
> > +       gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);
> > +       if (!gg_data.out_gpio) {
> > +               if (cfg_np->parent == np)
> > +                       desc = ERR_PTR(-ENXIO);
> > +               else
> > +                       desc = ERR_PTR(-EPROBE_DEFER);
> > +
> > +               goto out;
> > +       }
> > +
> > +       if (xlate_flags & OF_GPIO_ACTIVE_LOW)
> > +               req_flags |= GPIOF_ACTIVE_LOW;
> > +
> > +       if (of_property_read_bool(cfg_np, "input")) {
> > +               req_flags |= GPIOF_DIR_IN;
> > +       } else if (of_property_read_bool(cfg_np, "output-high")) {
> > +               req_flags |= GPIOF_INIT_HIGH;
> > +       } else if (!of_property_read_bool(cfg_np, "output-low")) {
> > +               desc = ERR_PTR(-EINVAL);
> > +               goto out;
> > +       }
> 
> That's why I would prefer a "direction" property instead of these 3
> ones: because if you have the following node:
> 
> line_foo {
>         gpios = <1 GPIO_ACTIVE_HIGH>;
>         input;
>         output-high;
> };
> 
> Then this code will not trigger an error and will just configure the
> GPIO as input.

Understood.

> 
> > +
> > +       if (of_property_read_bool(cfg_np, "open-drain-line"))
> > +               req_flags |= GPIOF_OPEN_DRAIN;
> > +
> > +       if (of_property_read_bool(cfg_np, "open-source-line"))
> > +               req_flags |= GPIOF_OPEN_DRAIN;
> > +
> > +       if (name && of_property_read_string(cfg_np, "line-name", name))
> > +               *name = cfg_np->name;
> > +
> > +       if (flags)
> > +               *flags = req_flags;
> > +
> > +       desc = gg_data.out_gpio;
> > +
> > +out:
> > +       of_node_put(cfg_np);
> > +
> > +       return desc;
> > +}
> > +
> > +/**
> >   * of_gpio_simple_xlate - translate gpio_spec to the GPIO number and flags
> >   * @gc:                pointer to the gpio_chip structure
> >   * @np:                device node of the GPIO chip
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index e8e98ca..b6f5bdb 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -55,6 +55,9 @@ static DEFINE_MUTEX(gpio_lookup_lock);
> >  static LIST_HEAD(gpio_lookup_list);
> >  LIST_HEAD(gpio_chips);
> >
> > +struct gpio_desc *__must_check gpiod_get_hog_index(struct device *dev,
> > +                                                  unsigned int idx);
> > +
> >  static inline void desc_set_label(struct gpio_desc *d, const char *label)
> >  {
> >         d->label = label;
> > @@ -226,6 +229,8 @@ int gpiochip_add(struct gpio_chip *chip)
> >         int             status = 0;
> >         unsigned        id;
> >         int             base = chip->base;
> > +       struct gpio_desc        *desc;
> > +       int             i;
> >
> >         if ((!gpio_is_valid(base) || !gpio_is_valid(base + chip->ngpio - 1))
> >                         && base >= 0) {
> > @@ -275,6 +280,16 @@ int gpiochip_add(struct gpio_chip *chip)
> >         of_gpiochip_add(chip);
> >         acpi_gpiochip_add(chip);
> >
> > +       /*
> > +        * Instantiate GPIO hogs
> > +        * There shouldn't be mores hogs then gpio available on this chip
> 
> s/then/than

Will fix.

> 
> > +        */
> > +       for (i = 0; i < chip->ngpio; i++) {
> > +               desc = gpiod_get_hog_index(chip->dev, i);
> > +               if (IS_ERR(desc))
> > +                       break;
> > +       }
> 
> chip->ngpio? Isn't there a better way to know the number of phandles
> in your gpio-hogs property?

Maybe there is. I'll look into it.

> 
> Also you may have an error returned either because you reached the end
> of the list, or because the hog configuration itself failed. In the
> latter case don't you want to continue to go through the list?
Understood.

> 
> Finally your desc variable should be declared within this loop since
> it is not used elsewhere.
> 
Understood.

> > +
> >         if (status)
> >                 goto fail;
> >
> > @@ -1742,6 +1757,72 @@ struct gpio_desc *__must_check __gpiod_get_index_optional(struct device *dev,
> >  EXPORT_SYMBOL_GPL(__gpiod_get_index_optional);
> >
> >  /**
> > + * gpiod_get_hog_index - obtain a GPIO from a multi-index GPIO hog
> > + * @dev:       GPIO consumer
> > + * @idx:       index of the GPIO to obtain
> > + *
> > + * This should only be used by the gpiochip_add to request/set GPIO initial
> > + * configuration.
> > + *
> > + * Return a valid GPIO descriptor, or an IS_ERR() condition in case of error.
> > + */
> > +struct gpio_desc *__must_check gpiod_get_hog_index(struct device *dev,
> > +                                                  unsigned int idx)
> > +{
> > +       struct gpio_desc *desc = NULL;
> > +       int err;
> > +       unsigned long flags;
> > +       const char *name;
> > +
> > +       /* Using device tree? */
> > +       if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
> > +               desc = of_get_gpio_hog(dev->of_node, idx, &name, &flags);
> > +
> > +       if (!desc)
> > +               return ERR_PTR(-ENOTSUPP);
> > +       else if (IS_ERR(desc))
> > +               return desc;
> > +
> > +       dev_dbg(dev, "gpio-hog: GPIO:%d (%s) as %s%s\n",
> > +               desc_to_gpio(desc), name, (flags&GPIOF_DIR_IN)?"input":"output",
> > +               (flags&GPIOF_DIR_IN)?"":(flags&GPIOF_INIT_HIGH)?"/high":"/low");
> > +
> 
> ...

I guess this means to remove the dev_dbg code?

> 
> > +       err = gpiod_request(desc, name);
> > +       if (err)
> > +               return ERR_PTR(err);
> > +
> > +       if (flags & GPIOF_OPEN_DRAIN)
> > +               set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> > +
> > +       if (flags & GPIOF_OPEN_SOURCE)
> > +               set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> > +
> > +       if (flags & GPIOF_ACTIVE_LOW)
> > +               set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> > +
> > +       if (flags & GPIOF_DIR_IN)
> > +               err = gpiod_direction_input(desc);
> > +       else
> > +               err = gpiod_direction_output_raw(desc,
> > +                               (flags & GPIOF_INIT_HIGH) ? 1 : 0);
> > +
> 
> This part of the code is very similar to what is found in
> __gpiod_get_index. Could you maybe try to extract the common code into
> its own function and call it from both sites instead of duplicating
> code?

Agreed.
Originally I was making use of gpio_request_one, but then I noticed it was move to the "_legacy" and would probably dissapear.

> 
> > +       if (err)
> > +               goto free_gpio;
> > +
> > +       if (flags & GPIOF_EXPORT) {
> > +               err = gpiod_export(desc, flags & GPIOF_EXPORT_CHANGEABLE);
> > +               if (err)
> > +                       goto free_gpio;
> 
> Right now export is not possible so I don't think you need that block.

Unless the export feature is requested along with this pacth.

> 
> > +       }
> > +
> > +       return desc;
> > +
> > +free_gpio:
> > +       gpiod_free(desc);
> > +       return ERR_PTR(err);
> > +}
> > +
> > +/**
> >   * gpiod_put - dispose of a GPIO descriptor
> >   * @desc:      GPIO descriptor to dispose of
> >   *
> > diff --git a/include/linux/of_gpio.h b/include/linux/of_gpio.h
> > index 38fc050..52d154c 100644
> > --- a/include/linux/of_gpio.h
> > +++ b/include/linux/of_gpio.h
> > @@ -59,6 +59,9 @@ extern int of_gpio_simple_xlate(struct gpio_chip *gc,
> >                                 const struct of_phandle_args *gpiospec,
> >                                 u32 *flags);
> >
> > +extern struct gpio_desc *of_get_gpio_hog(struct device_node *np, int index,
> > +                                        const char **name,
> > +                                        unsigned long *flags);
> 
> This function is gpiolib-private, therefore it should be declared in
> drivers/gpio/gpiolib.h alongside with the declaration of
> of_get_named_gpiod_flags.

Ah yes would be much better.

> 
> If I understood the latest discussions correctly we might want to add
> an export (and named export) feature on top of this patch. Linus, am I
> correct to understand that you are not opposed to both features? In
> this case, we might want to go ahead with the merging of one of the
> named GPIOs patches, so that Jiri and Pantelis can implement export
> based on this patch.
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