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Date: Fri, 19 Dec 2014 15:00:52 +0900
From: Alexandre Courbot <gnurou@...il.com>
To: Benoit Parrot <bparrot@...com>
Cc: Linus Walleij <linus.walleij@...aro.org>,
"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Maxime Ripard <maxime.ripard@...e-electrons.com>,
Jiri Prchal <jiri.prchal@...ignal.cz>,
Pantelis Antoniou <panto@...oniou-consulting.com>
Subject: Re: [Patch v4 1/2] gpio: add GPIO hogging mechanism
On Fri, Dec 19, 2014 at 2:08 AM, Benoit Parrot <bparrot@...com> wrote:
> Alexandre Courbot <gnurou@...il.com> wrote on Wed [2014-Dec-17 17:41:51 +0900]:
>> Looks ok to me. I have a few nits below, but otherwise I am happy with
>> how it turned out:
>>
>> Reviewed-by: Alexandre Courbot <acourbot@...dia.com>
> I'll add this to the next version.
>
>>
>> Thanks for your patience with this!
>>
>> On Sat, Dec 13, 2014 at 7:07 AM, Benoit Parrot <bparrot@...com> wrote:
>> > 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
>>
>> s/initally/initially
>>
>> > when the gpio controller is probed.
>>
>> GPIO in capitals please.
>>
>> >
>> > The actual DT scanning to collect the GPIO specific data is performed
>> > as part of the gpiochip_add().
>>
>> d/the
>>
>> >
>> > The purpose of this is to allows specific GPIOs to be configured
>>
>> s/allows/allow
>>
>> > without any driver specific code.
>> > This particularly useful because board design are getting
>>
>> This is particularly
>>
>> > increasingly complex and given SoC pins can now have upward
>> > of
>>
>> s/upward of/up to?
>
> well i meant more than 10 I think in some cases we have 13.
>
>>
>> > 10 mux values a lot of connections are now dependent on
>>
>> seems like a comma is missing here.
>>
>> > external IO muxes to switch various modes and combination.
>>
>> not sure what a combination is in that context.
>>
>> >
>> > 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 <bparrot@...com>
>> > ---
>> > Changes since v3:
>> > * Relocated the non-DT "hog" function to gpiolib.c.
>> > * Rename some of the function to be clearer and remove _ prefixes.
>> > * Replace the gpiod_request/gpiod_put usage with
>> > gpiochip_request_own_desc/free_own_desc version instead.
>> > * Refactor some of the logic to better handle error condition/reporting
>> > * Renamed the "direction" DT properties to "state".
>> >
>> > drivers/gpio/gpiolib-of.c | 119 ++++++++++++++++++++++++++++++++++++++++++
>> > drivers/gpio/gpiolib.c | 128 ++++++++++++++++++++++++++++++++++++++--------
>> > drivers/gpio/gpiolib.h | 3 ++
>> > 3 files changed, 230 insertions(+), 20 deletions(-)
>> >
>> > diff --git a/drivers/gpio/gpiolib-of.c b/drivers/gpio/gpiolib-of.c
>> > index 604dbe6..5422216 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 +112,122 @@ 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,
>>
>> out_gpio will be set to NULL if you don't specify it, so you don't
>> need this last line.
>
> ok
>
>>
>> > + };
>> > + 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, "state", &dir_val)) {
>> > + pr_warn("%s: GPIO:%d (%s): no hogging state specified, bailing out\n",
>> > + __func__, desc_to_gpio(gg_data.out_gpio), np->name);
>> > + return ERR_PTR(-EINVAL);
>> > + }
>> > +
>> > + 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 {
>> > + pr_warn("%s: GPIO:%d (%s): invalid state '%s' requested, bailing out\n",
>> > + __func__, desc_to_gpio(gg_data.out_gpio),
>> > + np->name, dir_val);
>> > + return ERR_PTR(-EINVAL);
>> > + }
>> > +
>> > + if (name && of_property_read_string(np, "line-name", name))
>> > + *name = np->name;
>> > +
>> > + desc = gg_data.out_gpio;
>> > +
>> > + return desc;
>> > +}
>> > +
>> > +/**
>> > + * of_gpiochip_scan_hogs - 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 of_gpiochip_scan_hogs(struct gpio_chip *chip)
>> > +{
>> > + 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) {
>
> As I was backporting this to 3.14 for my own purpose.
> I encountered a NULL pointer dereference here.
> In 3.14 chip->dev (which is optional) is NULL at least on my platform.
> I had to change the above line to:
>
> for_each_child_of_node(chip->of_node, np) {
>
> Would you recommend the same change here?
That looks ok, yes. IIRC chip->of_node is precisely here because
chip->dev might be NULL sometimes.
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