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SubjectRe: [PATCH/RFC 2/2] gpio: of: Add DT overlay support for GPIO hogs
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On 1/6/20 5:34 PM, Frank Rowand wrote:
> On 12/30/19 7:38 AM, Geert Uytterhoeven wrote:
>> As GPIO hogs are configured at GPIO controller initialization time,
>> adding/removing GPIO hogs in DT overlays does not work.
>>
>> Add support for GPIO hogs described in DT overlays by registering an OF
>> reconfiguration notifier, to handle the addition and removal of GPIO hog
>> subnodes to/from a GPIO controller device node.
>>
>> Note that when a GPIO hog device node is being removed, its "gpios"
>> properties is no longer available, so we have to keep track of which
>> node a hog belongs to, which is done by adding a pointer to the hog's
>> device node to struct gpio_desc.
>
> If I have read the patches and the existing overlay source correctly,
> then some observations:
>
> - A gpio hog node added in an overlay will be properly processed.
>
> - A gpio hog node already existing in the live devicetree, but with a
> non-active status will be properly processed if the status of the
> gpio hog node is changed to "ok" in the overlay.
>
> - If a gpio hog node already exists in the live devicetree with an
> active status, then any updated or added properties in that gpio
> hog node in the overlay will have no effect.
>
> There is a scenario where the updated property would have an effect:
> apply a second overlay that sets the status to inactive, then apply
> a third overlay that sets the status back to active. This is a
> rather contrived example and I think it should be documented as
> not supported and the result undefined.

I went back and double checked the related code. For gpio hog nodes
that are in a non-overlay, the status property is checked because
of_gpiochip_scan_gpios() uses for_each_available_child_of_node()
to search for gpio hog nodes, and for_each_available_child_of_node()
checks the status property. But in the case of a gpio hog node
added by an overlay, of_gpio_notify() does not check the status
property in the gpio hog node. The check for the status property
should be added to of_gpio_notify().

-Frank

>
> It would be good to document this explicitly.
>
>
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
>> ---
>> drivers/gpio/gpiolib-of.c | 84 +++++++++++++++++++++++++++++++++++++++
>> drivers/gpio/gpiolib-of.h | 2 +
>> drivers/gpio/gpiolib.c | 14 +++++--
>> drivers/gpio/gpiolib.h | 3 ++
>> 4 files changed, 100 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
>> index dfae797846bb746b..89a6138ac0a4b506 100644
>> --- a/drivers/gpio/gpiolib-of.c
>> +++ b/drivers/gpio/gpiolib-of.c
>> @@ -649,6 +649,10 @@ static int of_gpiochip_add_hog(struct gpio_chip *chip, struct device_node *hog)
>> ret = gpiod_hog(desc, name, lflags, dflags);
>> if (ret < 0)
>> return ret;
>> +
>> +#ifdef CONFIG_OF_DYNAMIC
>> + desc->hog = hog;
>> +#endif
>> }
>>
>> return 0;
>> @@ -676,11 +680,91 @@ static int of_gpiochip_scan_gpios(struct gpio_chip *chip)
>> of_node_put(np);
>> return ret;
>> }
>> +
>> + of_node_set_flag(np, OF_POPULATED);
>> }
>>
>> return 0;
>> }
>>
>> +#ifdef CONFIG_OF_DYNAMIC
>> +/**
>> + * of_gpiochip_remove_hog - Remove all hogs in a hog device node
>> + * @chip: gpio chip to act on
>> + * @hog: device node describing the hogs
>> + */
>> +static void of_gpiochip_remove_hog(struct gpio_chip *chip,
>> + struct device_node *hog)
>> +{
>> + struct gpio_desc *descs = chip->gpiodev->descs;
>> + unsigned int i;
>> +
>> + for (i = 0; i < chip->ngpio; i++) {
>> + if (test_bit(FLAG_IS_HOGGED, &descs[i].flags) &&
>> + descs[i].hog == hog)
>> + gpiochip_free_own_desc(&descs[i]);
>> + }
>> +}
>> +
>> +static int of_gpiochip_match_node(struct gpio_chip *chip, void *data)
>> +{
>> + return chip->gpiodev->dev.of_node == data;
>> +}
>> +
>> +static struct gpio_chip *of_find_gpiochip_by_node(struct device_node *np)
>> +{
>> + return gpiochip_find(np, of_gpiochip_match_node);
>> +}
>> +
>> +static int of_gpio_notify(struct notifier_block *nb, unsigned long action,
>> + void *arg)
>> +{
>> + struct of_reconfig_data *rd = arg;
>> + struct gpio_chip *chip;
>> + int ret;
>> +
>> + switch (of_reconfig_get_state_change(action, arg)) {
>> + case OF_RECONFIG_CHANGE_ADD:
>> + if (!of_property_read_bool(rd->dn, "gpio-hog"))
>> + return NOTIFY_OK; /* not for us */
>> +
>> + if (of_node_test_and_set_flag(rd->dn, OF_POPULATED))
>> + return NOTIFY_OK;
>
> I don't think OF_POPULATED could be already set. It seems to be a
> bug if it is.
>
>
>> +
>> + chip = of_find_gpiochip_by_node(rd->dn->parent);
>> + if (chip == NULL)
>> + return NOTIFY_OK; /* not for us */
>
> If I understand correctly, "not for us" is a misleading comment.
> The notification is for the node rd->dn->parent, but the device
> does not exist, so we can't do the hogging at the moment. (If the
> device is created later, then the gpio hog child node will exist,
> and the init will "do the right thing" with the hog node -- so
> not a problem.)
>
>
>> +
>> + ret = of_gpiochip_add_hog(chip, rd->dn);
>> + if (ret < 0) {
>> + pr_err("%s: failed to add hogs for %pOF\n", __func__,
>> + rd->dn);
>> + of_node_clear_flag(rd->dn, OF_POPULATED);
>> + return notifier_from_errno(ret);
>> + }
>> + break;
>> +
>> + case OF_RECONFIG_CHANGE_REMOVE:
>> + if (!of_node_check_flag(rd->dn, OF_POPULATED))
>> + return NOTIFY_OK; /* already depopulated */
>
> I don't think OF_POPULATED could be already cleared. It seems to be a
> bug if it is.
>
>> +
>> + chip = of_find_gpiochip_by_node(rd->dn->parent);
>> + if (chip == NULL)
>> + return NOTIFY_OK; /* not for us */
>
> Again, a misleading comment.
>
>> +
>> + of_gpiochip_remove_hog(chip, rd->dn);
>> + of_node_clear_flag(rd->dn, OF_POPULATED);
>> + break;
>> + }
>> +
>> + return NOTIFY_OK;
>> +}
>> +
>> +struct notifier_block gpio_of_notifier = {
>> + .notifier_call = of_gpio_notify,
>> +};
>> +#endif /* CONFIG_OF_DYNAMIC */
>> +
>> /**
>> * of_gpio_simple_xlate - translate gpiospec to the GPIO number and flags
>> * @gc: pointer to the gpio_chip structure
>> diff --git a/drivers/gpio/gpiolib-of.h b/drivers/gpio/gpiolib-of.h
>> index 9768831b1fe2f25b..ed26664f153782fc 100644
>> --- a/drivers/gpio/gpiolib-of.h
>> +++ b/drivers/gpio/gpiolib-of.h
>> @@ -35,4 +35,6 @@ static inline bool of_gpio_need_valid_mask(const struct gpio_chip *gc)
>> }
>> #endif /* CONFIG_OF_GPIO */
>>
>> +extern struct notifier_block gpio_of_notifier;
>> +
>> #endif /* GPIOLIB_OF_H */
>> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
>> index bff5ac774d870b67..ef12cfcaf0962c1c 100644
>> --- a/drivers/gpio/gpiolib.c
>> +++ b/drivers/gpio/gpiolib.c
>> @@ -2952,6 +2952,9 @@ static bool gpiod_free_commit(struct gpio_desc *desc)
>> clear_bit(FLAG_PULL_DOWN, &desc->flags);
>> clear_bit(FLAG_BIAS_DISABLE, &desc->flags);
>> clear_bit(FLAG_IS_HOGGED, &desc->flags);
>> +#ifdef CONFIG_OF_DYNAMIC
>> + desc->hog = NULL;
>> +#endif
>> ret = true;
>> }
>>
>> @@ -5145,10 +5148,15 @@ static int __init gpiolib_dev_init(void)
>> if (ret < 0) {
>> pr_err("gpiolib: failed to allocate char dev region\n");
>> bus_unregister(&gpio_bus_type);
>> - } else {
>> - gpiolib_initialized = true;
>> - gpiochip_setup_devs();
>> + return ret;
>> }
>> +
>> + gpiolib_initialized = true;
>> + gpiochip_setup_devs();
>> +
>> + if (IS_ENABLED(CONFIG_OF_DYNAMIC))
>> + WARN_ON(of_reconfig_notifier_register(&gpio_of_notifier));
>> +
>> return ret;
>> }
>> core_initcall(gpiolib_dev_init);
>> diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h
>> index a4a759920faa48ab..7af9931e8572304a 100644
>> --- a/drivers/gpio/gpiolib.h
>> +++ b/drivers/gpio/gpiolib.h
>> @@ -118,6 +118,9 @@ struct gpio_desc {
>> const char *label;
>> /* Name of the GPIO */
>> const char *name;
>> +#ifdef CONFIG_OF_DYNAMIC
>> + struct device_node *hog;
>> +#endif
>> };
>>
>> int gpiod_request(struct gpio_desc *desc, const char *label);
>>
>
>

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