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[media] dvb_frontend: improve documentation on set_delivery_system()

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While this patch change some things, the updated fields there are
used just on printk, so it shouldn't cause any functional changes.

Yet, this routine is a little complex, so explain a little more
how it works.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Mauro Carvalho Chehab 2012-01-05 14:39:05 -02:00
parent 9474c5e63f
commit 37fa53c6a1
1 changed files with 18 additions and 9 deletions
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27
drivers/media/dvb/dvb-core/dvb_frontend.c
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@ -1440,9 +1440,13 @@ static int set_delivery_system(struct dvb_frontend *fe, u32 desired_system)
if (desired_system == SYS_UNDEFINED) {
/*
* A DVBv3 call doesn't know what's the desired system.
* So, don't change the current delivery system. Instead,
* find the closest DVBv3 system that matches the delivery
* system.
* Also, DVBv3 applications don't know that ops.info->type
* could be changed, and they simply dies when it doesn't
* match.
* So, don't change the current delivery system, as it
* may be trying to do the wrong thing, like setting an
* ISDB-T frontend as DVB-T. Instead, find the closest
* DVBv3 system that matches the delivery system.
*/
if (is_dvbv3_delsys(c->delivery_system)) {
dprintk("%s() Using delivery system to %d\n",
@ -1452,27 +1456,29 @@ static int set_delivery_system(struct dvb_frontend *fe, u32 desired_system)
type = dvbv3_type(c->delivery_system);
switch (type) {
case DVBV3_QPSK:
desired_system = FE_QPSK;
desired_system = SYS_DVBS;
break;
case DVBV3_QAM:
desired_system = FE_QAM;
desired_system = SYS_DVBC_ANNEX_A;
break;
case DVBV3_ATSC:
desired_system = FE_ATSC;
desired_system = SYS_ATSC;
break;
case DVBV3_OFDM:
desired_system = FE_OFDM;
desired_system = SYS_DVBT;
break;
default:
dprintk("%s(): This frontend doesn't support DVBv3 calls\n",
__func__);
return -EINVAL;
}
delsys = c->delivery_system;
} else {
/*
* Check if the desired delivery system is supported
* This is a DVBv5 call. So, it likely knows the supported
* delivery systems.
*/
/* Check if the desired delivery system is supported */
ncaps = 0;
while (fe->ops.delsys[ncaps] && ncaps < MAX_DELSYS) {
if (fe->ops.delsys[ncaps] == desired_system) {
@ -1518,6 +1524,9 @@ static int set_delivery_system(struct dvb_frontend *fe, u32 desired_system)
}
/*
* The DVBv3 or DVBv5 call is requesting a different system. So,
* emulation is needed.
*
* Emulate newer delivery systems like ISDBT, DVBT and DMBTH
* for older DVBv5 applications. The emulation will try to use
* the auto mode for most things, and will assume that the desired