From f926dfc112bc6cf41d7068ee5e3f261e13a5bec8 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Sun, 10 Sep 2017 19:26:22 +0200 Subject: [PATCH] gpio: Make it possible for consumers to enforce open drain Some busses, like I2C, strictly need to have the line handled as open drain, i.e. not actively driven high. For this reason the i2c-gpio.c bit-banged I2C driver is reimplementing open drain handling outside of gpiolib. This is not very optimal. Instead make it possible for a consumer to explcitly express that the line must be handled as open drain instead of allowing local hacks papering over this issue. The descriptor tables, whether DT, ACPI or board files, should of course have flagged these lines as open drain. E.g.: enum gpio_lookup_flags GPIO_OPEN_DRAIN for a board file, or gpios = <&foo 42 GPIO_ACTIVE_HIGH|GPIO_OPEN_DRAIN>; in a device tree using But more often than not, these descriptors are wrong. So we need to make it possible for consumers to enforce this open drain behaviour. We now have two new enumerated GPIO descriptor config flags: GPIOD_OUT_LOW_OPEN_DRAIN and GPIOD_OUT_HIGH_OPEN_DRAIN that will set up the lined enforced as open drain as output low or high, using open drain (if the driver supports it) or using open drain emulation (setting the line as input to drive it high) from the gpiolib core. Cc: linux-gpio@vger.kernel.org Tested-by: Geert Uytterhoeven Signed-off-by: Linus Walleij --- drivers/gpio/gpiolib.c | 13 +++++++++++++ include/linux/gpio/consumer.h | 6 ++++++ 2 files changed, 19 insertions(+) diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index eb80dac4e26a..c952ef1b2f46 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -3264,8 +3264,21 @@ int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id, if (lflags & GPIO_ACTIVE_LOW) set_bit(FLAG_ACTIVE_LOW, &desc->flags); + if (lflags & GPIO_OPEN_DRAIN) set_bit(FLAG_OPEN_DRAIN, &desc->flags); + else if (dflags & GPIOD_FLAGS_BIT_OPEN_DRAIN) { + /* + * This enforces open drain mode from the consumer side. + * This is necessary for some busses like I2C, but the lookup + * should *REALLY* have specified them as open drain in the + * first place, so print a little warning here. + */ + set_bit(FLAG_OPEN_DRAIN, &desc->flags); + gpiod_warn(desc, + "enforced open drain please flag it properly in DT/ACPI DSDT/board file\n"); + } + if (lflags & GPIO_OPEN_SOURCE) set_bit(FLAG_OPEN_SOURCE, &desc->flags); if (lflags & GPIO_SLEEP_MAY_LOOSE_VALUE) diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h index 8f702fcbe485..5f72a49d1aa3 100644 --- a/include/linux/gpio/consumer.h +++ b/include/linux/gpio/consumer.h @@ -28,6 +28,7 @@ struct gpio_descs { #define GPIOD_FLAGS_BIT_DIR_SET BIT(0) #define GPIOD_FLAGS_BIT_DIR_OUT BIT(1) #define GPIOD_FLAGS_BIT_DIR_VAL BIT(2) +#define GPIOD_FLAGS_BIT_OPEN_DRAIN BIT(3) /** * Optional flags that can be passed to one of gpiod_* to configure direction @@ -39,6 +40,11 @@ enum gpiod_flags { GPIOD_OUT_LOW = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT, GPIOD_OUT_HIGH = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT | GPIOD_FLAGS_BIT_DIR_VAL, + GPIOD_OUT_LOW_OPEN_DRAIN = GPIOD_FLAGS_BIT_DIR_SET | + GPIOD_FLAGS_BIT_DIR_OUT | GPIOD_FLAGS_BIT_OPEN_DRAIN, + GPIOD_OUT_HIGH_OPEN_DRAIN = GPIOD_FLAGS_BIT_DIR_SET | + GPIOD_FLAGS_BIT_DIR_OUT | GPIOD_FLAGS_BIT_DIR_VAL | + GPIOD_FLAGS_BIT_OPEN_DRAIN, }; #ifdef CONFIG_GPIOLIB