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Subject: Re: [PATCH v2 2/2] gpio: of: Add DT overlay support for GPIO hogs
To:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>
Cc:     Peter Ujfalusi <peter.ujfalusi@ti.com>,
        Chris Brandt <chris.brandt@renesas.com>,
        linux-gpio@vger.kernel.org, devicetree@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org,
        Frank Rowand <frowand.list@gmail.com>
References: <20200220130149.26283-1-geert+renesas@glider.be>
 <20200220130149.26283-3-geert+renesas@glider.be>
From:   Frank Rowand <frowand.list@gmail.com>
Message-ID: <cad0d0a1-9838-55d3-a13e-29d8d5ae7f12@gmail.com>
Date:   Thu, 20 Feb 2020 12:51:22 -0600
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On 2/20/20 7:01 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.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
> v2:
>   - Drop RFC state,
>   - Document that modifying existing gpio-hog nodes is not supported.
> ---
>  drivers/gpio/gpiolib-of.c | 90 +++++++++++++++++++++++++++++++++++++++
>  drivers/gpio/gpiolib-of.h |  2 +
>  drivers/gpio/gpiolib.c    | 14 ++++--
>  drivers/gpio/gpiolib.h    |  3 ++
>  4 files changed, 106 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
> index 2b47f93886075294..ccc449df3792ae97 100644
> --- a/drivers/gpio/gpiolib-of.c
> +++ b/drivers/gpio/gpiolib-of.c
> @@ -628,6 +628,10 @@ 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;
> @@ -655,11 +659,97 @@ 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;
> +
> +	/*
> +	 * This only supports adding and removing complete gpio-hog nodes.
> +	 * Modifying an existing gpio-hog node is not supported (except for
> +	 * changing its "status" property, which is treated the same as
> +	 * addition/removal).
> +	 */
> +	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;
> +
> +		chip = of_find_gpiochip_by_node(rd->dn->parent);
> +		if (chip == NULL)
> +			return NOTIFY_OK;	/* not for us */
> +
> +		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 */
> +
> +		chip = of_find_gpiochip_by_node(rd->dn->parent);
> +		if (chip == NULL)
> +			return NOTIFY_OK;	/* not for us */
> +
> +		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 56de871060ea211e..6f312220fe80acaf 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -2925,6 +2925,9 @@ 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;
>  	}
>  
> @@ -5126,10 +5129,15 @@ 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 3e0aab2945d82974..18c75e83fd7679ec 100644
> --- a/drivers/gpio/gpiolib.h
> +++ b/drivers/gpio/gpiolib.h
> @@ -119,6 +119,9 @@ 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);
> 

Reviewed-by: Frank Rowand <frank.rowand@sony.com>