Hi, Linus Walleij <linus.walleij@xxxxxxxxxx> writes: > On Wed, Nov 29, 2017 at 2:56 PM, Felipe Balbi > <felipe.balbi@xxxxxxxxxxxxxxx> wrote: >> Me: >>> For the other thing: timestamping of GPIO events, we already >>> support timestamps for userspace GPIOs, but all it does is use >>> the kernel time, see gpiolib.c: >>> >>> static irqreturn_t lineevent_irq_thread(int irq, void *p) >>> { >>> struct lineevent_state *le = p; >>> struct gpioevent_data ge; >>> int ret, level; >>> >>> ge.timestamp = ktime_get_real_ns(); >>> level = gpiod_get_value_cansleep(le->desc); >> >> this is running as a thread with interrupts enabled, AFAICT. This means >> this thread can be preempted at least on PREEMPT_RT kernels, so your >> timestamp can be wrong, right? > > Yes, it can be off. What we should do to get i better is > something like what I did in: > drivers/iio/gyro/mpu3050-core.c > > Here I have both a hard and a soft IRQ handler (fast/slow if > you like) and take the timestamp in the hard IRQ, then use > it in the thread. > > This should be done identically in gpiolib to increase precision > in the general case. > > I was thinking about it already when implementing it but it fell > out of my mind. I'm putting in on my TODO. (CC to bartosz > who might be interested, he's using these ABIs quite a bit.) fair enough. In that case, it'll probably be easier to implement HW-based timestamping with something like below: modified drivers/gpio/gpiolib.c @@ -731,7 +731,11 @@ static irqreturn_t lineevent_irq_thread(int irq, void *p) struct gpioevent_data ge; int ret, level; - ge.timestamp = ktime_get_real_ns(); + if (le->desc->flags & FLAG_HAS_HW_TIMESTAMP) + ge.timestamp = gpio_get_hw_timestamp(le->desc); + else + ge.timestamp = ktime_get_real_ns(); + level = gpiod_get_value_cansleep(le->desc); if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE modified drivers/gpio/gpiolib.h @@ -206,6 +206,7 @@ struct gpio_desc { #define FLAG_USED_AS_IRQ 9 /* GPIO is connected to an IRQ */ #define FLAG_IS_HOGGED 11 /* GPIO is hogged */ #define FLAG_SLEEP_MAY_LOSE_VALUE 12 /* GPIO may lose value in sleep */ +#define FLAG_HAS_HW_TIMESTAMP 13 /* GPIO has HW-based timestamping */ /* Connection label */ const char *label; We may even extract ktime_get_real_ns() to gpio_get_timestamp() and do the branching in that function, like: modified drivers/gpio/gpiolib.c @@ -731,7 +731,7 @@ static irqreturn_t lineevent_irq_thread(int irq, void *p) struct gpioevent_data ge; int ret, level; - ge.timestamp = ktime_get_real_ns(); + ge.timestamp = gpiod_get_timestamp(le->desc); level = gpiod_get_value_cansleep(le->desc); if (le->eflags & GPIOEVENT_REQUEST_RISING_EDGE @@ -3155,6 +3155,14 @@ int gpiod_get_value_cansleep(const struct gpio_desc *desc) } EXPORT_SYMBOL_GPL(gpiod_get_value_cansleep); +u64 gpiod_get_timestamp(const struct gpio_desc *desc) +{ + if (desc->flags & FLAG_HAS_HW_TIMESTAMP) + return gpiod_get_raw_timestamp(desc); + else + return ktime_get_real_ns(); +} + /** * gpiod_get_raw_array_value_cansleep() - read raw values from an array of GPIOs * @array_size: number of elements in the descriptor / value arrays modified drivers/gpio/gpiolib.h @@ -206,6 +206,7 @@ struct gpio_desc { #define FLAG_USED_AS_IRQ 9 /* GPIO is connected to an IRQ */ #define FLAG_IS_HOGGED 11 /* GPIO is hogged */ #define FLAG_SLEEP_MAY_LOSE_VALUE 12 /* GPIO may lose value in sleep */ +#define FLAG_HAS_HW_TIMESTAMP 13 /* GPIO has HW-based timestamping */ /* Connection label */ const char *label; -- balbi
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