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gpio-sch: set output level after configuration of direction

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According to the datasheet, writing to the level register has no effect
when GPIO is programmed as input. Actually the the level register is
read-only when configured as input. Thus presetting the output level
before switching to output is _NOT_ possible. Any writes are lost!
Hence we set the level after configuring the GPIO as output.
But we cannot prevent a short low pulse if direction is set to high and
an external  pull-up is connected.

Signed-off-by: Daniel Krueger <daniel.krueger@systec-electronic.com>
Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
This commit is contained in:
Daniel Krueger 2014-04-07 14:20:32 +02:00 committed by Linus Walleij
parent 9ea8d8102b
commit 1e0d982317
1 changed files with 22 additions and 4 deletions
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26
drivers/gpio/gpio-sch.c
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@ -97,8 +97,6 @@ static int sch_gpio_core_direction_out(struct gpio_chip *gc,
u8 curr_dirs;
unsigned short offset, bit;
sch_gpio_core_set(gc, gpio_num, val);
spin_lock(&gpio_lock);
offset = CGIO + gpio_num / 8;
@ -109,6 +107,17 @@ static int sch_gpio_core_direction_out(struct gpio_chip *gc,
outb(curr_dirs & ~(1 << bit), gpio_ba + offset);
spin_unlock(&gpio_lock);
/*
* according to the datasheet, writing to the level register has no
* effect when GPIO is programmed as input.
* Actually the the level register is read-only when configured as input.
* Thus presetting the output level before switching to output is _NOT_ possible.
* Hence we set the level after configuring the GPIO as output.
* But we cannot prevent a short low pulse if direction is set to high
* and an external pull-up is connected.
*/
sch_gpio_core_set(gc, gpio_num, val);
return 0;
}
@ -178,8 +187,6 @@ static int sch_gpio_resume_direction_out(struct gpio_chip *gc,
u8 curr_dirs;
unsigned short offset, bit;
sch_gpio_resume_set(gc, gpio_num, val);
offset = RGIO + gpio_num / 8;
bit = gpio_num % 8;
@ -190,6 +197,17 @@ static int sch_gpio_resume_direction_out(struct gpio_chip *gc,
outb(curr_dirs & ~(1 << bit), gpio_ba + offset);
spin_unlock(&gpio_lock);
/*
* according to the datasheet, writing to the level register has no
* effect when GPIO is programmed as input.
* Actually the the level register is read-only when configured as input.
* Thus presetting the output level before switching to output is _NOT_ possible.
* Hence we set the level after configuring the GPIO as output.
* But we cannot prevent a short low pulse if direction is set to high
* and an external pull-up is connected.
*/
sch_gpio_resume_set(gc, gpio_num, val);
return 0;
}