[v2] gpio: convince line to become input in irq helper

Message ID CACRpkdZpRSrt4u_h11ROavVFZDh6OYJ49gJ6eD0y4gGuOxzMYg@mail.gmail.com
State New
Headers show

Commit Message

Linus Walleij July 5, 2016, 2:52 p.m.
I sent a patch for the direction setter to be more careful, but
it's no silver bullet for strange semantics.

On Tue, Jul 5, 2016 at 12:07 PM, Geert Uytterhoeven
<geert@linux-m68k.org> wrote:

> [1] gpio_rcar e6052000.gpio: sense irq = 11, type = 8

>     ravb e6800000.ethernet eth0: Base address at 0xe6800000,

> 2e:09:0a:00:83:1e, IRQ 131.

>     ...

> [2] gpiochip_irq_reqres: gpiochip e6052000.gpio

> [3] gpio_rcar e6052000.gpio: gpio_rcar_direction_input: 11

> [4] gpiochip_irq_reqres: desc->flags = 0x0

(...)
> This configures the GPIO for plain input mode, cfr. [3] above, basically

> undoing the configuration from [1]. Hence interrupts no longer come through,

> and Ethernet fails.


The driver is a bit fragile in that it relies on a certain call semantic,
I guess it is not a widespread problem so we should be able to make
a local fix if necessary.

The .set_direction() call should
set the direction. Why is it turning off interrupts as a side effect?

What happens if you apply this, making the .request() function handle
the pin setup and .set_direction() really just setting the
direction?

      */
@@ -234,14 +247,8 @@ static void
gpio_rcar_config_general_input_output_mode(struct gpio_chip *chip,
     /* Select "General Input/Output Mode" in IOINTSEL */
     gpio_rcar_modify_bit(p, IOINTSEL, gpio, false);

-    /* Select Input Mode or Output Mode in INOUTSEL */
-    gpio_rcar_modify_bit(p, INOUTSEL, gpio, output);
-
     spin_unlock_irqrestore(&p->lock, flags);
-}

-static int gpio_rcar_request(struct gpio_chip *chip, unsigned offset)
-{
     return pinctrl_request_gpio(chip->base + offset);
 }

.request() is always called before .set_direction() when issuing
gpiod_get() anyways, so the order required according to the comment
will be satisfied when the GPIO is first requested, but if we're just
using the interrupt, we still will be able to set the direction right.

Yours,
Linus Walleij
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Comments

Linus Walleij July 6, 2016, 12:38 p.m. | #1
On Wed, Jul 6, 2016 at 11:07 AM, Grygorii Strashko
<grygorii.strashko@ti.com> wrote:

> first of all for slow GPIO controllers (like pcf857x) it might be unsafe to call

> .direction_input() from .irq_request_resources() callback because it

> will be called in atomic context under raw_spin_lock_irqsave().

>

>

> __setup_irq

>    |- raw_spin_lock_irqsave()

>         |- irq_request_resources()

>         |- [ __irq_set_trigger() ]

>         |- [ irq_startup() ]

>         |- [ __enable_irq() ]

>    |- raw_spin_unlock_irqrestore()

>

> [and it can be unsafe for fast GPIO chips also ;( , for example if it's

> required to do some kind of PM management actions before accessing HW - most of

> drivers expect their GPIOchip callbacks to be called only after gpiochip.request() or

> .irq_startup().]

>

> In  my opinion this change breaks orthogonality of IRQchip vs GPIOchip interfaces

> because it adds and (what is more important) hides call of GPIOchip callback

> from inside IRQchip interface somewhere in  the depths of gpiolib framework.

> As result, GPIO drivers lose possibility to properly handle GPIO vs IRQ interface's

> differences like: locking, slow vs fast, hw specific settings, features of frameworks.

>

> I propose to revert it, sry,


Aw typical, you are right.

OK I'll take this patch and it's fixes out of the GPIO tree :(

Yours,
Linus Walleij
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Patch hide | download patch | download mbox

diff --git a/drivers/gpio/gpio-rcar.c b/drivers/gpio/gpio-rcar.c
index 681c93fb9e70..68fb0147caf4 100644
--- a/drivers/gpio/gpio-rcar.c
+++ b/drivers/gpio/gpio-rcar.c
@@ -221,7 +221,20 @@  static void
gpio_rcar_config_general_input_output_mode(struct gpio_chip *chip,
     struct gpio_rcar_priv *p = gpiochip_get_data(chip);
     unsigned long flags;

-    /* follow steps in the GPIO documentation for
+    spin_lock_irqsave(&p->lock, flags);
+
+    /* Select Input Mode or Output Mode in INOUTSEL */
+    gpio_rcar_modify_bit(p, INOUTSEL, gpio, output);
+
+    spin_unlock_irqrestore(&p->lock, flags);
+}
+
+static int gpio_rcar_request(struct gpio_chip *chip, unsigned offset)
+{
+    struct gpio_rcar_priv *p = gpiochip_get_data(chip);
+
+    /*
+     * follow steps in the GPIO documentation for
      * "Setting General Output Mode" and
      * "Setting General Input Mode"