The lchan_avail_by_type() attempts to find an unused lchan for the
given GSM_LCHAN_* value: TCH/F, TCH/H, or SDCCH. This is achieved
by looking up timeslots with compatible GSM_PCHAN_* values.
For instance, finding an unused SDCCH lchan may involve:
* attempt to find a timeslot with pchan=GSM_PCHAN_CCCH_SDCCH4,
* attempt to find a timeslot with pchan=GSM_PCHAN_CCCH_SDCCH4_CBCH,
* attempt to find a timeslot with pchan=GSM_PCHAN_SDCCH8_SACCH8C,
* attempt to find a timeslot with pchan=GSM_PCHAN_SDCCH8_SACCH8C_CBCH,
* attempt to find a timeslot with pchan=GSM_PCHAN_OSMO_DYN (switched),
* attempt to find a timeslot with pchan=GSM_PCHAN_OSMO_DYN (not switched).
Each attempt involves iterating over all timeslots of each TRX,
either in ascending or in descending order (see _lc_dyn_find_bts()
and _lc_find_trx()).
This patch simplifies the lookup logic by preparing a monolithic
array of timeslot pointers once, and then using that array for
each GSM_PCHAN_* lookup attempt. This change is required for the
upcoming dynamic channel allocation mode, which is fa more complex
than the existing ascending/descending ones.
A side effect of this change is that the interference aware mode
of allocation is not limited by the scope of a single TRX anymore.
Interference levels are now compared within the scope of the whole
BTS, so that lchans on the other TRXes may be picked if they are
better according to the interference reports from the BTS.
Change-Id: I7ccc56856bfd40fd7c63b7437736de60c2b516ff
Related: SYS#5460
Vadim Yanitskiy
ff9d3a64dc