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Date:	Mon, 2 Dec 2013 13:49:43 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Rhyland Klein <rklein@...dia.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] gpio: better lookup method for platform GPIOs

On Mon, Dec 2, 2013 at 1:01 PM, Alexandre Courbot <acourbot@...dia.com> wrote:
> Change the format of the platform GPIO lookup tables to make them less
> confusing and improve lookup efficiency.
>
> The previous format was a single linked-list that required to compare
> the device name and function ID of every single GPIO defined for each
> lookup. Switch that to a list of per-device tables, so that the lookup
> can be done in two steps, omitting the GPIOs that are not relevant for a
> particular device.
>
> The matching rules are now defined as follows:
> - The device name must match *exactly*, and can be NULL for GPIOs not
>   assigned to a particular device,
> - If the function ID in the lookup table is NULL, the con_id argument of
>   gpiod_get() will not be used for lookup. However, if it is defined, it
>   must match exactly.
> - The index must always match.

Thanks for an updated version.
Few minor comments below.
Comments about loops are here as well.

I any case:
Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

>
> Signed-off-by: Alexandre Courbot <acourbot@...dia.com>
> Acked-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---
> Changes since v1:
> - Applied most fixes suggested by Andy
> - Hopefully safer and less confusing table lookup algorithm
> - Added Mika's ack
>
>  Documentation/gpio/board.txt |  25 ++++++----
>  drivers/gpio/gpiolib.c       | 109 +++++++++++++++++++++++--------------------
>  include/linux/gpio/driver.h  |  22 ++++-----
>  3 files changed, 85 insertions(+), 71 deletions(-)
>
> diff --git a/Documentation/gpio/board.txt b/Documentation/gpio/board.txt
> index 0d03506f2cc5..a4fdd96cef93 100644
> --- a/Documentation/gpio/board.txt
> +++ b/Documentation/gpio/board.txt
> @@ -72,10 +72,11 @@ where
>
>    - chip_label is the label of the gpiod_chip instance providing the GPIO
>    - chip_hwnum is the hardware number of the GPIO within the chip
> -  - dev_id is the identifier of the device that will make use of this GPIO. If
> -       NULL, the GPIO will be available to all devices.
> +  - dev_id is the identifier of the device that will make use of this GPIO. It
> +       can be NULL, in which case it will be matched for calls to gpiod_get()
> +       with a NULL device.
>    - con_id is the name of the GPIO function from the device point of view. It
> -       can be NULL.
> +       can be NULL, in which case it will match any function.
>    - idx is the index of the GPIO within the function.
>    - flags is defined to specify the following properties:
>         * GPIOF_ACTIVE_LOW      - to configure the GPIO as active-low
> @@ -88,16 +89,20 @@ Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
>
>  A lookup table can then be defined as follows:
>
> -       struct gpiod_lookup gpios_table[] = {
> -       GPIO_LOOKUP_IDX("gpio.0", 15, "foo.0", "led", 0, GPIO_ACTIVE_HIGH),
> -       GPIO_LOOKUP_IDX("gpio.0", 16, "foo.0", "led", 1, GPIO_ACTIVE_HIGH),
> -       GPIO_LOOKUP_IDX("gpio.0", 17, "foo.0", "led", 2, GPIO_ACTIVE_HIGH),
> -       GPIO_LOOKUP("gpio.0", 1, "foo.0", "power", GPIO_ACTIVE_LOW),
> -       };
> +struct gpiod_lookup_table gpios_table = {
> +       .dev_id = "foo.0",
> +       .size = 4,
> +       .table = {
> +               GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
> +               GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
> +               GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
> +               GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
> +       },
> +};
>
>  And the table can be added by the board code as follows:
>
> -       gpiod_add_table(gpios_table, ARRAY_SIZE(gpios_table));
> +       gpiod_add_lookup_table(&gpios_table);
>
>  The driver controlling "foo.0" will then be able to obtain its GPIOs as follows:
>
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index f72618ba716a..d17d6eabed6a 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2259,18 +2259,14 @@ void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
>  EXPORT_SYMBOL_GPL(gpiod_set_value_cansleep);
>
>  /**
> - * gpiod_add_table() - register GPIO device consumers
> - * @table: array of consumers to register
> - * @num: number of consumers in table
> + * gpiod_add_lookup_table() - register GPIO device consumers
> + * @table: table of consumers to register
>   */
> -void gpiod_add_table(struct gpiod_lookup *table, size_t size)
> +void gpiod_add_lookup_table(struct gpiod_lookup_table *table)
>  {
>         mutex_lock(&gpio_lookup_lock);
>
> -       while (size--) {
> -               list_add_tail(&table->list, &gpio_lookup_list);
> -               table++;
> -       }
> +       list_add_tail(&table->list, &gpio_lookup_list);
>
>         mutex_unlock(&gpio_lookup_lock);
>  }
> @@ -2326,72 +2322,85 @@ static struct gpio_desc *acpi_find_gpio(struct device *dev, const char *con_id,
>         return desc;
>  }
>
> -static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
> -                                   unsigned int idx,
> -                                   enum gpio_lookup_flags *flags)
> +static struct gpiod_lookup_table *gpiod_find_lookup_table(struct device *dev)
>  {
>         const char *dev_id = dev ? dev_name(dev) : NULL;
> -       struct gpio_desc *desc = ERR_PTR(-ENODEV);
> -       unsigned int match, best = 0;
> -       struct gpiod_lookup *p;
> +       struct gpiod_lookup_table *table;
>
>         mutex_lock(&gpio_lookup_lock);
>
> -       list_for_each_entry(p, &gpio_lookup_list, list) {
> -               match = 0;
> +       list_for_each_entry(table, &gpio_lookup_list, list) {
> +               if (table->dev_id && dev_id) {
> +                       /*
> +                        * Valid strings on both ends, must be identical to have
> +                        * a match
> +                        */
> +                       if (!strcmp(table->dev_id, dev_id))
> +                               goto end;
> +               } else {
> +                       /*
> +                        * One of the pointers is NULL, so both must be to have
> +                        * a match
> +                        */
> +                       if (dev_id == table->dev_id)
> +                               goto end;
> +               }

Yes, in this case it looks clearer. Though, you might join last else
and if in one line.

> +       }
> +       table = NULL;

Up to you, though I think it's clearer to return NULL explicitly (and
unlock mutex before).

>
> -               if (p->dev_id) {
> -                       if (!dev_id || strcmp(p->dev_id, dev_id))
> -                               continue;
> +end:

Maybe 'found' suits better?

> +       mutex_unlock(&gpio_lookup_lock);
> +       return table;
> +}
>
> -                       match += 2;
> -               }
> +static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
> +                                   unsigned int idx,
> +                                   enum gpio_lookup_flags *flags)
> +{
> +       struct gpio_desc *desc = ERR_PTR(-ENODEV);
> +       struct gpiod_lookup_table *table;
> +       int i;
>
> -               if (p->con_id) {
> -                       if (!con_id || strcmp(p->con_id, con_id))
> -                               continue;
> +       table = gpiod_find_lookup_table(dev);
> +       if (!table)
> +               return desc;
>
> -                       match += 1;
> -               }
> +       for (i = 0; i < table->size; i++) {
> +               struct gpio_chip *chip;
> +               struct gpiod_lookup *p = &table->table[i];
>
> +               /* idx must always match exactly */
>                 if (p->idx != idx)
>                         continue;
>
> -               if (match > best) {
> -                       struct gpio_chip *chip;
> -
> -                       chip = find_chip_by_name(p->chip_label);
> -
> -                       if (!chip) {
> -                               dev_warn(dev, "cannot find GPIO chip %s\n",
> -                                        p->chip_label);
> -                               continue;
> -                       }
> +               /* If the lookup entry has a con_id, require exact match */
> +               if (p->con_id && (!con_id || strcmp(p->con_id, con_id)))
> +                       continue;
>
> -                       if (chip->ngpio <= p->chip_hwnum) {
> -                               dev_warn(dev, "GPIO chip %s has %d GPIOs\n",
> -                                        chip->label, chip->ngpio);
> -                               continue;
> -                       }
> +               chip = find_chip_by_name(p->chip_label);
>
> -                       desc = gpio_to_desc(chip->base + p->chip_hwnum);
> -                       *flags = p->flags;
> +               if (!chip) {

> +                       dev_warn(dev, "cannot find GPIO chip %s\n",
> +                                p->chip_label);

Could it be one line?

> +                       continue;
> +               }
>
> -                       if (match != 3)
> -                               best = match;
> -                       else
> -                               break;
> +               if (chip->ngpio <= p->chip_hwnum) {
> +                       dev_warn(dev, "GPIO chip %s has %d GPIOs\n",
> +                                chip->label, chip->ngpio);
> +                       continue;
>                 }
> -       }
>
> -       mutex_unlock(&gpio_lookup_lock);
> +               desc = gpiochip_offset_to_desc(chip, p->chip_hwnum);
> +               *flags = p->flags;
> +       }
>
>         return desc;
>  }
>
>  /**
>   * gpio_get - obtain a GPIO for a given GPIO function
> - * @dev:       GPIO consumer
> + * @dev:       GPIO consumer, can be NULL for system-global GPIOs
>   * @con_id:    function within the GPIO consumer
>   *
>   * Return the GPIO descriptor corresponding to the function con_id of device
> diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
> index 3ea2cf6b0e6c..44893ef40817 100644
> --- a/include/linux/gpio/driver.h
> +++ b/include/linux/gpio/driver.h
> @@ -140,7 +140,6 @@ enum gpio_lookup_flags {
>   * platform data.
>   */
>  struct gpiod_lookup {
> -       struct list_head list;
>         /*
>          * name of the chip the GPIO belongs to
>          */
> @@ -150,10 +149,6 @@ struct gpiod_lookup {
>          */
>         u16 chip_hwnum;
>         /*
> -        * name of device that can claim this GPIO
> -        */
> -       const char *dev_id;
> -       /*
>          * name of the GPIO from the device's point of view
>          */
>         const char *con_id;
> @@ -167,28 +162,33 @@ struct gpiod_lookup {
>         enum gpio_lookup_flags flags;
>  };
>
> +struct gpiod_lookup_table {
> +       struct list_head list;
> +       const char *dev_id;
> +       unsigned int size;
> +       struct gpiod_lookup table[];
> +};
> +
>  /*
>   * Simple definition of a single GPIO under a con_id
>   */
> -#define GPIO_LOOKUP(_chip_label, _chip_hwnum, _dev_id, _con_id, _flags) \
> -       GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _dev_id, _con_id, 0, _flags)
> +#define GPIO_LOOKUP(_chip_label, _chip_hwnum, _con_id, _flags) \
> +       GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _con_id, 0, _flags)
>
>  /*
>   * Use this macro if you need to have several GPIOs under the same con_id.
>   * Each GPIO needs to use a different index and can be accessed using
>   * gpiod_get_index()
>   */
> -#define GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _dev_id, _con_id, _idx, \
> -                       _flags)                                           \
> +#define GPIO_LOOKUP_IDX(_chip_label, _chip_hwnum, _con_id, _idx, _flags)  \
>  {                                                                         \
>         .chip_label = _chip_label,                                        \
>         .chip_hwnum = _chip_hwnum,                                        \
> -       .dev_id = _dev_id,                                                \
>         .con_id = _con_id,                                                \
>         .idx = _idx,                                                      \
>         .flags = _flags,                                                  \
>  }
>
> -void gpiod_add_table(struct gpiod_lookup *table, size_t size);
> +void gpiod_add_lookup_table(struct gpiod_lookup_table *table);
>
>  #endif
> --
> 1.8.4.2
>



-- 
With Best Regards,
Andy Shevchenko
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