diff options
Diffstat (limited to 'drivers/gpio/gpio-sch.c')
| -rw-r--r-- | drivers/gpio/gpio-sch.c | 26 |
1 files changed, 22 insertions, 4 deletions
diff --git a/drivers/gpio/gpio-sch.c b/drivers/gpio/gpio-sch.c index 5af65719b95..a9b1cd16c84 100644 --- a/drivers/gpio/gpio-sch.c +++ b/drivers/gpio/gpio-sch.c @@ -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; } |