I see in drivers/media/dvb/dvb-core/dvb_frontend.c that there is some
synchronization between the old and the new API.
But it is incomplete: The new FE_GET_PROPERTY will report only cached
values, which is whatever the application has written and not the
actual tuned values like FE_GET_FRONTEND will. The problem is that
FE_GET_PROPERTY only will call fe->ops.get_property even for legacy
drivers. It could have fallen back to calling fe->ops.get_frontend
followed by a cache synchronization.
Is this difference intentional (because it costs too much, doesn't
matter, or whatever)? Or should I prepare a patch for dvb_frontend.c?
I made a small util comparing the two APIs, basically just doing
fd = open("/dev/dvb/adapter0/frontend0", O_RDONLY);
ioctl(fd, FE_GET_INFO, &fe_info);
ioctl(fd, FE_GET_FRONTEND, &fe_param);
ioctl(fd, FE_GET_PROPERTY, &dtv_props);
close(fd);
and pretty-printing some of the results from the three ioctl()s. It
reports typically something like this:
bjorn@canardo:~$ /tmp/dvb_fe_test /dev/dvb/adapter1/frontend0
== /dev/dvb/adapter1/frontend0 ==
name: Philips TDA10023 DVB-C
type: FE_QAM
== FE_GET_FRONTEND ==
frequency : 394013477
inversion : off (0)
symbol_rate : 6900000
fec_inner : FEC_NONE (0)
modulation : QAM_256 (5)
== FE_GET_PROPERTY ==
[17] DTV_DELIVERY_SYSTEM : SYS_DVBC_ANNEX_AC (1)
[03] DTV_FREQUENCY : 394000000
[06] DTV_INVERSION : auto (2)
[08] DTV_SYMBOL_RATE : 6900000
[09] DTV_INNER_FEC : FEC_AUTO (9)
[04] DTV_MODULATION : QAM_256 (5)
[35] DTV_API_VERSION : 5.1
[05] DTV_BANDWIDTH_HZ : BANDWIDTH_AUTO (3)
Notice how FE_GET_PROPERTY returns "auto" settings for inversion and
inner_fec, while FE_GET_FRONTEND reports the actual values currently set
in the tuner. Also notice how the frequency differs.
It's not a big issue I believe, but I do find this a bit confusing as
two different apps using different APIs will report different settings.
Bjørn
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