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Date: Mon, 04 Jul 2016 23:33:16 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Johan Hovold <johan@...nel.org>
Cc: Linus Walleij <linus.walleij@...aro.org>,
Alexandre Courbot <gnurou@...il.com>,
linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "gpiolib: Split GPIO flags parsing and GPIO configuration"
Hi Johan,
Thank you for the patch.
On Sunday 03 Jul 2016 18:32:05 Johan Hovold wrote:
> This reverts commit 923b93e451db876d1479d3e4458fce14fec31d1c.
>
> Make sure consumers do not overwrite gpio flags for pins that have
> already been claimed.
>
> While adding support for gpio drivers to refuse a request using
> unsupported flags, the order of when the requested flag was checked and
> the new flags were applied was reversed to that consumers could
> overwrite flags for already requested gpios.
>
> This not only affects device-tree setups where two drivers could request
> the same gpio using conflicting configurations, but also allowed user
> space to clear gpio flags for already claimed pins simply by attempting
> to export them through the sysfs interface. By for example clearing the
> FLAG_ACTIVE_LOW flag this way, user space could effectively change the
> polarity of a signal.
>
> Reverting this change obviously prevents gpio drivers from doing sanity
> checks on the flags in their request callbacks. Fortunately only one
> recently added driver (gpio-tps65218 in v4.6) appears to do this, and a
> follow up patch could restore this functionality through a different
> interface.
As we're not dealing with a v4.7 regression that would need to be applied this
week, can't you propose a proper fix instead of a revert ?
> Cc: stable <stable@...r.kernel.org> # 4.4
> Signed-off-by: Johan Hovold <johan@...nel.org>
> ---
> drivers/gpio/gpiolib-legacy.c | 8 +++----
> drivers/gpio/gpiolib.c | 52
> +++++++++++++------------------------------ 2 files changed, 20
> insertions(+), 40 deletions(-)
>
> diff --git a/drivers/gpio/gpiolib-legacy.c b/drivers/gpio/gpiolib-legacy.c
> index 3a5c7011ad3b..8b830996fe02 100644
> --- a/drivers/gpio/gpiolib-legacy.c
> +++ b/drivers/gpio/gpiolib-legacy.c
> @@ -28,6 +28,10 @@ int gpio_request_one(unsigned gpio, unsigned long flags,
> const char *label) if (!desc && gpio_is_valid(gpio))
> return -EPROBE_DEFER;
>
> + err = gpiod_request(desc, label);
> + if (err)
> + return err;
> +
> if (flags & GPIOF_OPEN_DRAIN)
> set_bit(FLAG_OPEN_DRAIN, &desc->flags);
>
> @@ -37,10 +41,6 @@ int gpio_request_one(unsigned gpio, unsigned long flags,
> const char *label) if (flags & GPIOF_ACTIVE_LOW)
> set_bit(FLAG_ACTIVE_LOW, &desc->flags);
>
> - err = gpiod_request(desc, label);
> - if (err)
> - return err;
> -
> if (flags & GPIOF_DIR_IN)
> err = gpiod_direction_input(desc);
> else
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 570771ed19e6..be74bd370f1f 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1352,14 +1352,6 @@ static int __gpiod_request(struct gpio_desc *desc,
> const char *label) spin_lock_irqsave(&gpio_lock, flags);
> }
> done:
> - if (status < 0) {
> - /* Clear flags that might have been set by the caller before
> - * requesting the GPIO.
> - */
> - clear_bit(FLAG_ACTIVE_LOW, &desc->flags);
> - clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
> - clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
> - }
> spin_unlock_irqrestore(&gpio_lock, flags);
> return status;
> }
> @@ -2587,28 +2579,13 @@ struct gpio_desc *__must_check
> gpiod_get_optional(struct device *dev, }
> EXPORT_SYMBOL_GPL(gpiod_get_optional);
>
> -/**
> - * gpiod_parse_flags - helper function to parse GPIO lookup flags
> - * @desc: gpio to be setup
> - * @lflags: gpio_lookup_flags - returned from of_find_gpio() or
> - * of_get_gpio_hog()
> - *
> - * Set the GPIO descriptor flags based on the given GPIO lookup flags.
> - */
> -static void gpiod_parse_flags(struct gpio_desc *desc, unsigned long lflags)
> -{
> - 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);
> -}
>
> /**
> * gpiod_configure_flags - 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
> @@ -2616,10 +2593,17 @@ static void gpiod_parse_flags(struct gpio_desc
> *desc, unsigned long lflags) * occurred while trying to acquire the GPIO.
> */
> static int gpiod_configure_flags(struct gpio_desc *desc, const char
> *con_id, - enum gpiod_flags dflags)
> + 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);
> @@ -2686,13 +2670,11 @@ struct gpio_desc *__must_check
> gpiod_get_index(struct device *dev, return desc;
> }
>
> - gpiod_parse_flags(desc, lookupflags);
> -
> status = gpiod_request(desc, con_id);
> if (status < 0)
> return ERR_PTR(status);
>
> - status = gpiod_configure_flags(desc, con_id, flags);
> + status = gpiod_configure_flags(desc, con_id, lookupflags, flags);
> if (status < 0) {
> dev_dbg(dev, "setup of GPIO %s failed\n", con_id);
> gpiod_put(desc);
> @@ -2748,6 +2730,10 @@ struct gpio_desc *fwnode_get_named_gpiod(struct
> fwnode_handle *fwnode, if (IS_ERR(desc))
> return desc;
>
> + ret = gpiod_request(desc, NULL);
> + if (ret)
> + return ERR_PTR(ret);
> +
> if (active_low)
> set_bit(FLAG_ACTIVE_LOW, &desc->flags);
>
> @@ -2758,10 +2744,6 @@ struct gpio_desc *fwnode_get_named_gpiod(struct
> fwnode_handle *fwnode, set_bit(FLAG_OPEN_SOURCE, &desc->flags);
> }
>
> - ret = gpiod_request(desc, NULL);
> - if (ret)
> - return ERR_PTR(ret);
> -
> return desc;
> }
> EXPORT_SYMBOL_GPL(fwnode_get_named_gpiod);
> @@ -2814,8 +2796,6 @@ int gpiod_hog(struct gpio_desc *desc, const char
> *name, chip = gpiod_to_chip(desc);
> hwnum = gpio_chip_hwgpio(desc);
>
> - gpiod_parse_flags(desc, lflags);
> -
> local_desc = gpiochip_request_own_desc(chip, hwnum, name);
> if (IS_ERR(local_desc)) {
> status = PTR_ERR(local_desc);
> @@ -2824,7 +2804,7 @@ int gpiod_hog(struct gpio_desc *desc, const char
> *name, return status;
> }
>
> - status = gpiod_configure_flags(desc, name, dflags);
> + status = gpiod_configure_flags(desc, name, lflags, dflags);
> if (status < 0) {
> pr_err("setup of hog GPIO %s (chip %s, offset %d) failed,
%d\n",
> name, chip->label, hwnum, status);
--
Regards,
Laurent Pinchart
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