From 4deea4cb471354a8abdeecc9a571dfdbac8c2481 Mon Sep 17 00:00:00 2001 From: Mauro Carvalho Chehab Date: Mon, 9 Nov 2015 23:24:10 -0200 Subject: [PATCH] [media] dvb: document dvb_frontend_sleep_until() This function is used mainly at the DVB core, in order to provide emulation for a legacy ioctl. The only current exception is the stv0299 driver, with takes more than 8ms to switch voltage, breaking the emulation for FE_DISHNETWORK_SEND_LEGACY_CMD. Document that. Signed-off-by: Mauro Carvalho Chehab --- drivers/media/dvb-core/dvb_frontend.c | 9 ++++---- drivers/media/dvb-core/dvb_frontend.h | 30 ++++++++++++++++++++++++++- 2 files changed, 34 insertions(+), 5 deletions(-) diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c index c38ef1a72b4a..d764cffb2102 100644 --- a/drivers/media/dvb-core/dvb_frontend.c +++ b/drivers/media/dvb-core/dvb_frontend.c @@ -891,10 +891,11 @@ static void dvb_frontend_stop(struct dvb_frontend *fe) } /* - * Sleep until gettimeofday() > waketime + add_usec - * This needs to be as precise as possible, but as the delay is - * usually between 2ms and 32ms, it is done using a scheduled msleep - * followed by usleep (normally a busy-wait loop) for the remainder + * Sleep for the amount of time given by add_usec parameter + * + * This needs to be as precise as possible, as it affects the detection of + * the dish tone command at the satellite subsystem. The precision is improved + * by using a scheduled msleep followed by udelay for the remainder. */ void dvb_frontend_sleep_until(ktime_t *waketime, u32 add_usec) { diff --git a/drivers/media/dvb-core/dvb_frontend.h b/drivers/media/dvb-core/dvb_frontend.h index 97661b2f247a..a6bc03718b1e 100644 --- a/drivers/media/dvb-core/dvb_frontend.h +++ b/drivers/media/dvb-core/dvb_frontend.h @@ -404,6 +404,11 @@ struct dtv_frontend_properties; * FE_ENABLE_HIGH_LNB_VOLTAGE ioctl (only Satellite). * @dishnetwork_send_legacy_command: callback function to implement the * FE_DISHNETWORK_SEND_LEGACY_CMD ioctl (only Satellite). + * Drivers should not use this, except when the DVB + * core emulation fails to provide proper support (e.g. + * if set_voltage() takes more than 8ms to work), and + * when backward compatibility with this legacy API is + * required. * @i2c_gate_ctrl: controls the I2C gate. Newer drivers should use I2C * mux support instead. * @ts_bus_ctrl: callback function used to take control of the TS bus. @@ -693,6 +698,29 @@ extern void dvb_frontend_reinitialise(struct dvb_frontend *fe); extern int dvb_frontend_suspend(struct dvb_frontend *fe); extern int dvb_frontend_resume(struct dvb_frontend *fe); -extern void dvb_frontend_sleep_until(ktime_t *waketime, u32 add_usec); +/** + * dvb_frontend_sleep_until() - Sleep for the amount of time given by + * add_usec parameter + * + * @waketime: pointer to a struct ktime_t + * @add_usec: time to sleep, in microseconds + * + * This function is used to measure the time required for the + * %FE_DISHNETWORK_SEND_LEGACY_CMD ioctl to work. It needs to be as precise + * as possible, as it affects the detection of the dish tone command at the + * satellite subsystem. + * + * Its used internally by the DVB frontend core, in order to emulate + * %FE_DISHNETWORK_SEND_LEGACY_CMD using the &dvb_frontend_ops.set_voltage() + * callback. + * + * NOTE: it should not be used at the drivers, as the emulation for the + * legacy callback is provided by the Kernel. The only situation where this + * should be at the drivers is when there are some bugs at the hardware that + * would prevent the core emulation to work. On such cases, the driver would + * be writing a &dvb_frontend_ops.dishnetwork_send_legacy_command() and + * calling this function directly. + */ +void dvb_frontend_sleep_until(ktime_t *waketime, u32 add_usec); #endif -- 2.20.1