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[media] dvb: document dvb_frontend_sleep_until()

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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 <mchehab@osg.samsung.com>
This commit is contained in:
Mauro Carvalho Chehab 2015-11-09 23:24:10 -02:00
parent 6747b39441
commit 4deea4cb47
2 changed files with 34 additions and 5 deletions
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9
drivers/media/dvb-core/dvb_frontend.c
View File

@ -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)
{

30
drivers/media/dvb-core/dvb_frontend.h
View File

@ -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