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SubjectRe: [PATCH 1/2] pinctrl: Allow a device to indicate when to force a state
On Thu, Sep 21, 2017 at 3:04 AM, Florian Fainelli <f.fainelli@gmail.com> wrote:

> It may happen that a device needs to force applying a state, e.g:
> because it only defines one state of pin states (default) but loses
> power/register contents when entering low power modes. Add a
> pinctrl_dev::flags bitmask to help describe future quirks and define
> PINCTRL_FLG_FORCE_STATE as such a settable flag.
>
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

But I'm uncertain about the design.

A while back, I applied this patch to the GPIO subsystem:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/linux/gpio/machine.h?id=05f479bf7d239f01ff6546f2bdeb14ad0fe65601

commit 05f479bf7d239f01ff6546f2bdeb14ad0fe65601
Author: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Date: Tue May 23 15:47:29 2017 +0100

gpio: Add new flags to control sleep status of GPIOs

Add new flags to allow users to specify that they are not concerned with
the status of GPIOs whilst in a sleep/low power state.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

diff --git a/include/linux/gpio/machine.h b/include/linux/gpio/machine.h
index c0d712d22b07..13adadf53c09 100644
--- a/include/linux/gpio/machine.h
+++ b/include/linux/gpio/machine.h
@@ -9,6 +9,8 @@ enum gpio_lookup_flags {
GPIO_ACTIVE_LOW = (1 << 0),
GPIO_OPEN_DRAIN = (1 << 1),
GPIO_OPEN_SOURCE = (1 << 2),
+ GPIO_SLEEP_MAINTAIN_VALUE = (0 << 3),
+ GPIO_SLEEP_MAY_LOOSE_VALUE = (1 << 3),
};

Charles is also working on pin control and will probably have some
input on design.

Maybe we could do the same: a flag to maintain the value and
a flag to allow it to be lost across suspend/resume, which is the
core issue here.
Your case is analogous to GPIO_SLEEP_MAY_LOOSE_VALUE
and you restore the state when you come back from sleep.

Note how gpiolib does this:

bool gpiochip_line_is_persistent(struct gpio_chip *chip, unsigned int offset)
{
if (offset >= chip->ngpio)
return false;
return !test_bit(FLAG_SLEEP_MAY_LOOSE_VALUE,
&chip->gpiodev->descs[offset].flags);
}
EXPORT_SYMBOL_GPL(gpiochip_line_is_persistent);
(Notice ! in front of test_bit(), the name of the function makes sense.)

Then the driver in drivers/gpio/gpio-arizona.c does some
special quirks like this:

static int arizona_gpio_direction_in(struct gpio_chip *chip, unsigned offset)
{
struct arizona_gpio *arizona_gpio = gpiochip_get_data(chip);
struct arizona *arizona = arizona_gpio->arizona;
bool persistent = gpiochip_line_is_persistent(chip, offset);
bool change;
int ret;
ret = regmap_update_bits_check(arizona->regmap,
ARIZONA_GPIO1_CTRL + offset,
ARIZONA_GPN_DIR, ARIZONA_GPN_DIR,
&change);
if (ret < 0)
return ret;
if (change && persistent) {
pm_runtime_mark_last_busy(chip->parent);
pm_runtime_put_autosuspend(chip->parent);
}
return 0;
}
So what this driver does is allow the GPIO block to loose power
using runtime PM if and only if the line is flagged as persistent, i.e. it
will not loose its state when sleeping, so let it sleep.

Next point, this commit from Baolin:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt?id=6606bc9dee63ad8cda2cc310d2ad5992673a785a

output-low - set the pin to output mode with low level
output-high - set the pin to output mode with high level
+sleep-hardware-state - indicate this is sleep related state which
will be programmed
+ into the registers for the sleep state.
slew-rate - set the slew rate

This is another thing: here we are defining a state that will be managed
by autonomous hardware. The state settings will be poked into some
special registers that will automatically take effect when the system
goes into sleep.

This is a hardware-induced state: the SLEEP line for the entire SoC
is asserted.

What you want is something different: a flag like:

sleep-restore-state - indicate that this state needs to be restored after sleep
as the hardware loose states when sleeping.

The driver could look for this in a more granular per-state manner, instead
of all states of the pin controller being restored, we mark what
states need to be restored on the way up after sleep.

What are your thoughts about this?

I do not rule out a global flag for the whole controller, it is just a bit
confusing if we start to have per-state, per-pin and per-controller
sleep behaviour. If we have to have this we have to, but I want to
fully understand the problem first.

Yours,
Linus Walleij

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