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Date: Mon, 2 Dec 2013 21:37:18 +0900
From: Alexandre Courbot <gnurou@...il.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Alexandre Courbot <acourbot@...dia.com>,
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 8:49 PM, Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
> 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>
Thanks!
>
>>
>> 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.
I don't think that would conform to the coding conventions. Will try
and see if checkpatch complains, but I'm rather confident it will...
>
>> + }
>> + table = NULL;
>
> Up to you, though I think it's clearer to return NULL explicitly (and
> unlock mutex before).
As v1 of this patch can attest, the less return statements in a
lock-holding function, the better. :)
>
>>
>> - if (p->dev_id) {
>> - if (!dev_id || strcmp(p->dev_id, dev_id))
>> - continue;
>> +end:
>
> Maybe 'found' suits better?
But we end up here even if we haven't "found" anything...
>
>> + 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?
The line would be 84 characters if we do that, unfortunately.
Thanks for the review!
Alex.
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