Thanks for the quick feedback.

Alexandre Courbot [off-list ref] wrote on Fri [2014-Dec-12 17:54:06 +0900]:

On Thu, Dec 11, 2014 at 8:48 AM, Benoit Parrot [off-list ref] wrote:

quoted

Alexandre Courbot [off-list ref] wrote on Wed [2014-Dec-10 20:19:51 +0900]:

quoted

On Fri, Dec 5, 2014 at 6:02 AM, Benoit Parrot [off-list ref] wrote:

quoted

Based on Boris Brezillion's work this is a reworked patch
of his initial GPIO hogging mechanism.
This patch provides a way to initally configure specific GPIO
when the gpio controller is probed.

The actual DT scanning to collect the GPIO specific data is performed
as part of the gpiochip_add().

The purpose of this is to allows specific GPIOs to be configured
without any driver specific code.
This particularly useful because board design are getting
increasingly complex and given SoC pins can now have upward
of 10 mux values a lot of connections are now dependent on
external IO muxes to switch various modes and combination.

Specific drivers should not necessarily need to be aware of
what accounts to a specific board implementation. This board level
"description" should be best kept as part of the dts file.

Signed-off-by: Benoit Parrot <redacted>
---
Changes since v2:
 * Refactor the gpio-hog mechanism to split the DT related action
   from the actual "hogging" operation.
 * This allows non-DT providers to implement hogs as well.
 * Added FLAG_IS_HOGGED to mark hogged gpio and make gpiochip removal
   able to release hogged gpio.
 * Similarly to the hogging, the cleanup is performed as part of
   of_gpiochip_remove
 * Refactor the gpio-hog mechanism as private functions meant to
   be to invoked from of_gpiochip_add().

Changes since v1:
 * Refactor the gpio-hog mechanism as private functions meant to
   be to invoked from of_gpiochip_add().

 drivers/gpio/gpiolib-of.c     | 127 ++++++++++++++++++++++++++++++++++++++++++
 drivers/gpio/gpiolib.c        | 118 ++++++++++++++++++++++++++++++---------
 drivers/gpio/gpiolib.h        |   1 +
 include/linux/gpio/consumer.h |   9 +++
 4 files changed, 229 insertions(+), 26 deletions(-)

diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
index 604dbe6..e13134d 100644
--- a/drivers/gpio/gpiolib-of.c
+++ b/drivers/gpio/gpiolib-of.c

@@ -22,6 +22,7 @@
 #include <linux/of_gpio.h>
 #include <linux/pinctrl/pinctrl.h>
 #include <linux/slab.h>
+#include <linux/gpio/machine.h>

 #include "gpiolib.h"

@@ -111,6 +112,128 @@ int of_get_named_gpio_flags(struct device_node *np, const char *list_name,
 EXPORT_SYMBOL(of_get_named_gpio_flags);

 /**
+ * of_get_gpio_hog() - Get a GPIO hog descriptor, names and flags for GPIO API
+ * @np:                device node to get GPIO from
+ * @name:      GPIO line name
+ * @flags:     a flags pointer to fill in
+ *
+ * Returns GPIO descriptor to use with Linux GPIO API, or one of the errno
+ * value on the error condition.
+ */
+
+static struct gpio_desc *of_get_gpio_hog(struct device_node *np,
+                                 const char **name,
+                                 enum gpio_lookup_flags *lflags,
+                                 enum gpiod_flags *dflags)
+{
+       struct device_node *chip_np;
+       enum of_gpio_flags xlate_flags;
+       struct gpio_desc *desc;
+       const char *dir_val;
+       struct gg_data gg_data = {
+               .flags = &xlate_flags,
+               .out_gpio = NULL,
+       };
+       u32 tmp;
+       int i, ret;
+
+       chip_np = np->parent;
+       if (!chip_np)
+               return ERR_PTR(-EINVAL);
+
+       xlate_flags = 0;
+       *lflags = 0;
+       *dflags = 0;
+
+       ret = of_property_read_u32(chip_np, "#gpio-cells", &tmp);
+       if (ret)
+               return ERR_PTR(ret);
+
+       if (tmp > MAX_PHANDLE_ARGS)
+               return ERR_PTR(-EINVAL);
+
+       gg_data.gpiospec.args_count = tmp;
+       gg_data.gpiospec.np = chip_np;
+       for (i = 0; i < tmp; i++) {
+               ret = of_property_read_u32_index(np, "gpios", i,
+                                          &gg_data.gpiospec.args[i]);
+               if (ret)
+                       return ERR_PTR(ret);
+       }
+
+       gpiochip_find(&gg_data, of_gpiochip_find_and_xlate);
+       if (!gg_data.out_gpio) {
+               if (np->parent == np)
+                       return ERR_PTR(-ENXIO);
+               else
+                       return ERR_PTR(-EPROBE_DEFER);
+       }
+
+       if (xlate_flags & OF_GPIO_ACTIVE_LOW)
+               *lflags |= GPIO_ACTIVE_LOW;
+
+       if (!of_property_read_string(np, "direction", &dir_val)) {
+               if (!strcmp(dir_val, "input"))
+                       *dflags |= GPIOD_IN;
+               else if (!strcmp(dir_val, "output-low"))
+                       *dflags |= GPIOD_OUT_LOW;
+               else if (!strcmp(dir_val, "output-high"))
+                       *dflags |= GPIOD_OUT_HIGH;
+       }

... else?

We should probably return an error if the property is not specified -
is there a point in hogging a GPIO without a direction? E.g:

if (of_property_read_string(np, "direction", &dir_val))
    return ERR_PTR(-EINVAL);

if (!strcmp(...

to use the nice pattern that errors (and not normal behavior) are the exception.

Bah, I was going for compartmentalization.
It make sense if you don't think about it ..... :)

quoted

quoted

+
+       if (name && of_property_read_string(np, "line-name", name))
+               *name = np->name;
+
+       desc = gg_data.out_gpio;
+
+       return desc;
+}
+
+/**
+ * _gpiochip_hog - Scan gpio-controller and apply GPIO hog as requested
+ * @chip:      gpio chip to act on
+ *
+ * This is only used by of_gpiochip_add to request/set GPIO initial
+ * configuration.
+ */
+static void _gpiochip_hog(struct gpio_chip *chip)

Rename to of_gpio_scan_hogs() maybe?

Given that it is meant for gpiochip_add, how about
_gpiochip_scan_hogs()?

of_gpiochip_scan_hogs(), and this is my last offer. :P (why do you
want to prefix it with __ btw?)

Not sure really the _ prefix just made them look more like private functions.
Not stuck up on it, though.

of_gpiochip_scan_hogs() it is.

quoted

quoted

quoted

+{
+       struct gpio_desc *desc = NULL;
+       struct device_node *np;
+       const char *name;
+       enum gpio_lookup_flags lflags;
+       enum gpiod_flags dflags;
+
+       for_each_child_of_node(chip->dev->of_node, np) {
+               if (!of_property_read_bool(np, "gpio-hog"))
+                       continue;
+
+               desc = of_get_gpio_hog(np, &name, &lflags, &dflags);
+               if (IS_ERR(desc))
+                       continue;
+
+               __gpiod_hog(desc, name, lflags, dflags);

You are not propagating any error returned by __gpiod_hog here.

_gpiochip_hog is a void function given that __gpiod_hog() is the last call of that loop
there is nothing to propagate.
You would still want to scan all of the child node regardless of errors, no?

You're right. Besides hogging failure should probably not be a fatal
error. In this case please make sure that all possible errors related
to hogging are at least reported accordingly in the log.

quoted

quoted

quoted

+       }
+}
+
+/**
+ * _gpiochip_unhog - Scan gpio-controller and apply GPIO hog as requested
+ * @chip:      gpio chip to act on
+ *
+ * This is only used by of_gpiochip_remove to free hogged gpios
+ *
+ */
+static void _gpiochip_unhog(struct gpio_chip *chip)
+{
+       int id;
+
+       for (id = 0; id < chip->ngpio; id++) {
+               if (test_bit(FLAG_IS_HOGGED, &chip->desc[id].flags))
+                       gpiod_put(&chip->desc[id]);
+       }
+}

This function is not DT-specific. It should be included in gpiolib.c
and called from there before of_gpiochip_remove().

Agreed, any name request while I am at it or tis this fine as is?

Name looks good, although I don't know why the '_' prefix?

I will change it to gpiochip_free_hogs()

quoted

quoted

quoted

+
+/**
  * of_gpio_simple_xlate - translate gpio_spec to the GPIO number and flags
  * @gc:                pointer to the gpio_chip structure
  * @np:                device node of the GPIO chip

@@ -302,10 +425,14 @@ void of_gpiochip_add(struct gpio_chip *chip)

        of_gpiochip_add_pin_range(chip);
        of_node_get(chip->of_node);
+
+       _gpiochip_hog(chip);
 }

 void of_gpiochip_remove(struct gpio_chip *chip)
 {
        gpiochip_remove_pin_ranges(chip);
        of_node_put(chip->of_node);
+
+       _gpiochip_unhog(chip);
 }

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index e8e98ca..4ef6eb8 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c

@@ -849,6 +849,7 @@ static bool __gpiod_free(struct gpio_desc *desc)
                clear_bit(FLAG_REQUESTED, &desc->flags);
                clear_bit(FLAG_OPEN_DRAIN, &desc->flags);
                clear_bit(FLAG_OPEN_SOURCE, &desc->flags);
+               clear_bit(FLAG_IS_HOGGED, &desc->flags);
                ret = true;
        }

@@ -1631,6 +1632,58 @@ struct gpio_desc *__must_check __gpiod_get_optional(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(__gpiod_get_optional);

+
+/**
+ * __gpiod_get_helper - helper function to request and configure a given GPIO
+ * @desc:      gpio whose value will be assigned
+ * @con_id:    unction 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
+ * requested function and/or index, or another IS_ERR() code if an error
+ * occurred while trying to acquire the GPIO.
+ */
+static int __gpiod_get_helper(struct gpio_desc *desc, const char *con_id,
+               unsigned long lflags, enum gpiod_flags dflags)
+{
+       int status;
+
+       status = gpiod_request(desc, con_id);

As I mentioned in the previous revision, this will prevent the module
from being unloaded with hogged GPIOs. You need to use
gpiochip_request_own_desc() here and gpiochip_free_own_desc() instead
of gpiod_put() to free hogged GPIOs. Therefore the call to
gpiod_request/gpiochip_request_own_gpio should be taken out of this
(very nice otherwise!) helper.

I can split the functionality out but I do not understand why in this case using
gpiod_request would prevent module from being unloaded?
Isn't gpiochip_remove() part of a gpio module unload sequence?

Because then the _gpiochip_unhog() would release these descriptors. Am I missing something?

This is because gpiod_request() does a try_module_get(), which will
cause an error when someone tries to unload the module with, say,
rmmod. The corresponding calls to gpiod_put() that would decrease the
module usage count are typically done at module unload time, and thus
never get a chance to be called.

Ok no problem I'll change that too.

quoted

Also would using gpiochip_request_own_desc() basically allow the very same hogged GPIO to be
requested later on by a consumer.

No, both gpiod_request() and gpiochip_request_own_desc() call
__gpiod_request(), which sets the FLAG_REQUESTED flag on the
descriptor, ensuring it cannot be requested again later.

Ok