Re: [Patch v4 1/2] gpio: add GPIO hogging mechanism

[Benoit Parrot <bparrot@ti.com>]

Alexandre Courbot <gnurou@gmail.com> wrote on Wed [2014-Dec-17 17:41:51 +0900]:
> Looks ok to me. I have a few nits below, but otherwise I am happy with
> how it turned out:
> 
> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
I'll add this to the next version.

> 
> Thanks for your patience with this!
> 
> On Sat, Dec 13, 2014 at 7:07 AM, Benoit Parrot <bparrot@ti.com> wrote:
> > Based on Boris Brezillion's work this is a reworked patch
> > of his initial GPIO hogging mechanism.
> > This patch provides a way to initally configure specific GPIO
> 
> s/initally/initially
> 
> > when the gpio controller is probed.
> 
> GPIO in capitals please.
> 
> >
> > The actual DT scanning to collect the GPIO specific data is performed
> > as part of the gpiochip_add().
> 
> d/the
> 
> >
> > The purpose of this is to allows specific GPIOs to be configured
> 
> s/allows/allow
> 
> > without any driver specific code.
> > This particularly useful because board design are getting
> 
> This is particularly
> 
> > increasingly complex and given SoC pins can now have upward
> > of
> 
> s/upward of/up to?

well i meant more than 10 I think in some cases we have 13.

> 
> > 10 mux values a lot of connections are now dependent on
> 
> seems like a comma is missing here.
> 
> > external IO muxes to switch various modes and combination.
> 
> not sure what a combination is in that context.
> 
> >
> > 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@ti.com>
> > ---
> > Changes since v3:
> >  * Relocated the non-DT "hog" function to gpiolib.c.
> >  * Rename some of the function to be clearer and remove _ prefixes.
> >  * Replace the gpiod_request/gpiod_put usage with
> >    gpiochip_request_own_desc/free_own_desc version instead.
> >  * Refactor some of the logic to better handle error condition/reporting
> >  * Renamed the "direction" DT properties to "state".
> >
> >  drivers/gpio/gpiolib-of.c | 119 ++++++++++++++++++++++++++++++++++++++++++
> >  drivers/gpio/gpiolib.c    | 128 ++++++++++++++++++++++++++++++++++++++--------
> >  drivers/gpio/gpiolib.h    |   3 ++
> >  3 files changed, 230 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> > index 604dbe6..5422216 100644
> > --- a/drivers/gpio/gpiolib-of.c
> > +++ b/drivers/gpio/gpiolib-of.c
> > @@ -22,6 +22,7 @@
> >  #include <linux/of_gpio.h>
> >  #include <linux/pinctrl/pinctrl.h>
> >  #include <linux/slab.h>
> > +#include <linux/gpio/machine.h>
> >
> >  #include "gpiolib.h"
> >
> > @@ -111,6 +112,122 @@ 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
> > + * @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.
> > + */
> > +
> > +static struct gpio_desc *of_get_gpio_hog(struct device_node *np,
> > +                                 const char **name,
> > +                                 enum gpio_lookup_flags *lflags,
> > +                                 enum gpiod_flags *dflags)
> > +{
> > +       struct device_node *chip_np;
> > +       enum of_gpio_flags xlate_flags;
> > +       struct gpio_desc *desc;
> > +       const char *dir_val;
> > +       struct gg_data gg_data = {
> > +               .flags = &xlate_flags,
> > +               .out_gpio = NULL,
> 
> out_gpio will be set to NULL if you don't specify it, so you don't
> need this last line.

ok

> 
> > +       };
> > +       u32 tmp;
> > +       int i, ret;
> > +
> > +       chip_np = np->parent;
> > +       if (!chip_np)
> > +               return ERR_PTR(-EINVAL);
> > +
> > +       xlate_flags = 0;
> > +       *lflags = 0;
> > +       *dflags = 0;
> > +
> > +       ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);
> > +       if (ret)
> > +               return ERR_PTR(ret);
> > +
> > +       if (tmp > MAX_PHANDLE_ARGS)
> > +               return ERR_PTR(-EINVAL);
> > +
> > +       gg_data.gpiospec.args_count = tmp;
> > +       gg_data.gpiospec.np = chip_np;
> > +       for (i = 0; i < tmp; i++) {
> > +               ret = of_property_read_u32_index(np, "gpios", i,
> > +                                          &gg_data.gpiospec.args[i]);
> > +               if (ret)
> > +                       return ERR_PTR(ret);
> > +       }
> > +
> > +       gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);
> > +       if (!gg_data.out_gpio) {
> > +               if (np->parent == np)
> > +                       return ERR_PTR(-ENXIO);
> > +               else
> > +                       return ERR_PTR(-EPROBE_DEFER);
> > +       }
> > +
> > +       if (xlate_flags & OF_GPIO_ACTIVE_LOW)
> > +               *lflags |= GPIO_ACTIVE_LOW;
> > +
> > +       if (of_property_read_string(np, "state", &dir_val)) {
> > +               pr_warn("%s: GPIO:%d (%s): no hogging state specified, bailing out\n",
> > +                        __func__, desc_to_gpio(gg_data.out_gpio), np->name);
> > +               return ERR_PTR(-EINVAL);
> > +       }
> > +
> > +       if (!strcmp(dir_val, "input"))
> > +               *dflags |= GPIOD_IN;
> > +       else if (!strcmp(dir_val, "output-low"))
> > +               *dflags |= GPIOD_OUT_LOW;
> > +       else if (!strcmp(dir_val, "output-high"))
> > +               *dflags |= GPIOD_OUT_HIGH;
> > +       else {
> > +               pr_warn("%s: GPIO:%d (%s): invalid state '%s' requested, bailing out\n",
> > +                        __func__, desc_to_gpio(gg_data.out_gpio),
> > +                       np->name, dir_val);
> > +               return ERR_PTR(-EINVAL);
> > +       }
> > +
> > +       if (name && of_property_read_string(np, "line-name", name))
> > +               *name = np->name;
> > +
> > +       desc = gg_data.out_gpio;
> > +
> > +       return desc;
> > +}
> > +
> > +/**
> > + * of_gpiochip_scan_hogs - Scan gpio-controller and apply GPIO hog as requested
> > + * @chip:      gpio chip to act on
> > + *
> > + * This is only used by of_gpiochip_add to request/set GPIO initial
> > + * configuration.
> > + */
> > +static void of_gpiochip_scan_hogs(struct gpio_chip *chip)
> > +{
> > +       struct gpio_desc *desc = NULL;
> > +       struct device_node *np;
> > +       const char *name;
> > +       enum gpio_lookup_flags lflags;
> > +       enum gpiod_flags dflags;
> > +
> > +       for_each_child_of_node(chip->dev->of_node, np) {

As I was backporting this to 3.14 for my own purpose.
I encountered a NULL pointer dereference here.
In 3.14 chip->dev (which is optional) is NULL at least on my platform.
I had to change the above line to:

       for_each_child_of_node(chip->of_node, np) {

Would you recommend the same change here?

> > +               if (!of_property_read_bool(np, "gpio-hog"))
> > +                       continue;
> > +
> > +               desc = of_get_gpio_hog(np, &name, &lflags, &dflags);
> > +               if (IS_ERR(desc))
> > +                       continue;
> > +
> > +               if (gpiod_hog(desc, name, lflags, dflags))
> > +                       continue;
> > +       }
> > +}
> > +
> > +/**
> >   * 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
> > @@ -302,6 +419,8 @@ void of_gpiochip_add(struct gpio_chip *chip)
> >
> >         of_gpiochip_add_pin_range(chip);
> >         of_node_get(chip->of_node);
> > +
> > +       of_gpiochip_scan_hogs(chip);
> >  }
> >
> >  void of_gpiochip_remove(struct gpio_chip *chip)
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index 58659db..5527dbb 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -301,6 +301,7 @@ EXPORT_SYMBOL_GPL(gpiochip_add);
> >
> >  /* Forward-declaration */
> >  static void gpiochip_irqchip_remove(struct gpio_chip *gpiochip);
> > +static void gpiochip_free_hogs(struct gpio_chip *chip);
> >
> >  /**
> >   * gpiochip_remove() - unregister a gpio_chip
> > @@ -319,6 +320,7 @@ void gpiochip_remove(struct gpio_chip *chip)
> >
> >         gpiochip_irqchip_remove(chip);
> >         gpiochip_remove_pin_ranges(chip);
> > +       gpiochip_free_hogs(chip);
> >         of_gpiochip_remove(chip);
> >
> >         for (id = 0; id < chip->ngpio; id++) {
> > @@ -849,6 +851,7 @@ static bool __gpiod_free(struct gpio_desc *desc)
> >                 clear_bit(FLAG_REQUESTED, &desc->flags);
> >                 clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
> >                 clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
> > +               clear_bit(FLAG_IS_HOGGED, &desc->flags);
> >                 ret = true;
> >         }
> >
> > @@ -1653,6 +1656,47 @@ struct gpio_desc *__must_check __gpiod_get_optional(struct device *dev,
> >  }
> >  EXPORT_SYMBOL_GPL(__gpiod_get_optional);
> >
> > +
> > +/**
> > + * __gpiod_set_helper - helper function to configure a given GPIO
> > + * @desc:      gpio whose value will be assigned
> > + * @con_id:    function within the GPIO consumer
> > + * @lflags:    gpio_lookup_flags - returned from of_find_gpio() or
> > + *             of_get_gpio_hog()
> > + * @dflags:    gpiod_flags - optional GPIO initialization flags
> > + *
> > + * Return 0 on success, -ENOENT if no GPIO has been assigned to the
> > + * requested function and/or index, or another IS_ERR() code if an error
> > + * occurred while trying to acquire the GPIO.
> > + */
> > +static int __gpiod_set_helper(struct gpio_desc *desc, const char *con_id,
> > +               unsigned long lflags, enum gpiod_flags dflags)
> > +{
> > +       int status;
> > +
> > +       if (lflags & GPIO_ACTIVE_LOW)
> > +               set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> > +       if (lflags & GPIO_OPEN_DRAIN)
> > +               set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> > +       if (lflags & GPIO_OPEN_SOURCE)
> > +               set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> > +
> > +       /* No particular flag request, return here... */
> > +       if (!(dflags & GPIOD_FLAGS_BIT_DIR_SET)) {
> > +               pr_debug("no flags found for %s\n", con_id);
> > +               return 0;
> > +       }
> > +
> > +       /* Process flags */
> > +       if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
> > +               status = gpiod_direction_output(desc,
> > +                                             dflags & GPIOD_FLAGS_BIT_DIR_VAL);
> > +       else
> > +               status = gpiod_direction_input(desc);
> > +
> > +       return status;
> > +}
> > +
> >  /**
> >   * gpiod_get_index - obtain a GPIO from a multi-index GPIO function
> >   * @dev:       GPIO consumer, can be NULL for system-global GPIOs
> > @@ -1702,30 +1746,12 @@ struct gpio_desc *__must_check __gpiod_get_index(struct device *dev,
> >         }
> >
> >         status = gpiod_request(desc, con_id);
> > -
> >         if (status < 0)
> >                 return ERR_PTR(status);
> >
> > -       if (lookupflags & GPIO_ACTIVE_LOW)
> > -               set_bit(FLAG_ACTIVE_LOW, &desc->flags);
> > -       if (lookupflags & GPIO_OPEN_DRAIN)
> > -               set_bit(FLAG_OPEN_DRAIN, &desc->flags);
> > -       if (lookupflags & GPIO_OPEN_SOURCE)
> > -               set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> > -
> > -       /* No particular flag request, return here... */
> > -       if (!(flags & GPIOD_FLAGS_BIT_DIR_SET))
> > -               return desc;
> > -
> > -       /* Process flags */
> > -       if (flags & GPIOD_FLAGS_BIT_DIR_OUT)
> > -               status = gpiod_direction_output(desc,
> > -                                             flags & GPIOD_FLAGS_BIT_DIR_VAL);
> > -       else
> > -               status = gpiod_direction_input(desc);
> > -
> > +       status = __gpiod_set_helper(desc, con_id, lookupflags, flags);
> >         if (status < 0) {
> > -               dev_dbg(dev, "setup of GPIO %s failed\n", con_id);
> > +               pr_debug("setup of GPIO %s failed\n", con_id);
> >                 gpiod_put(desc);
> >                 return ERR_PTR(status);
> >         }
> > @@ -1819,6 +1845,68 @@ struct gpio_desc *__must_check __gpiod_get_index_optional(struct device *dev,
> >  EXPORT_SYMBOL_GPL(__gpiod_get_index_optional);
> >
> >  /**
> > + * gpiod_hog - Hog the specified GPIO desc given the provided flags
> > + * @desc:      gpio whose value will be assigned
> > + * @name:      gpio line name
> > + * @lflags:    gpio_lookup_flags - returned from of_find_gpio() or
> > + *             of_get_gpio_hog()
> > + * @dflags:    gpiod_flags - optional GPIO initialization flags
> > + *
> > + */
> > +int gpiod_hog(struct gpio_desc *desc, const char *name,
> > +             unsigned long lflags, enum gpiod_flags dflags)
> > +{
> > +       struct gpio_chip *chip;
> > +       struct gpio_desc *local_desc;
> > +       int hwnum;
> > +       int status;
> > +
> > +       chip = gpiod_to_chip(desc);
> > +       hwnum = gpio_chip_hwgpio(desc);
> > +
> > +       local_desc = gpiochip_request_own_desc(chip, hwnum, name);
> 
> This looks somehow funny because local_desc will be strictly equal to
> desc, but there is nothing you can do here. The DT GPIO lookup process
> should not return a desc, but a (gpiochip*, hwnum) tuple to begin
> with, so let's keep it that way. I made a note to myself to fix this.

Yeah it does, I was almost tempted to add a check to make sure local_desc
would be identical to desc. :)