Voice output serial port is enabled on some Huawei models (e.g. E169)
without problems, but for example on E173u-2 it is never enabled
during an incoming call. There might also be other Huawei models
having the same issue.
I traced the issue down to "^DDSETEX" AT command, which is used
to notify the device to start streaming audio. It seems that Ofono
sends this command too early on incoming calls. The command should
always be sent *after* the dial "D" or answer "A" command. The patch
fixes this behavior and afterwards voice will also work on E173u-2.
This patch was generated by the following semantic patch
(http://coccinelle.lip6.fr/)
// <smpl>
@fix disable is_null,isnt_null1@
expression *E;
@@
- !E
+ E == NULL
// </smpl>