Re: help testing a vchiq patch

On Thu, Aug 20, 2026 at 08:54:17PM +0100, Marco Devesas Campos wrote:
> Hi Bob
> 
> > However, there's no hint of any audio output via an old Dell monitor with integrated
> > HDMI audio which I know works.
> 
> What happens when you ‘cat </dev/random >/dev/dsp’ (maybe as root?)
> 
Permission denied as a regular user, as root a panic:
login: Aug 20 16:52:57 nemesis su[3694]: bob to root on /dev/pts/2
panic: _mtx_lock_sleep: recursed on non-recursive mutex dsp0.play.0 @ /usr/src/sys/dev/sound/pcm/channel.c:590

cpuid = 0
time = 1787269981
KDB: stack backtrace:
db_trace_self() at db_trace_self
db_trace_self_wrapper() at db_trace_self_wrapper+0x44
vpanic() at vpanic+0x1c8
panic() at panic+0x48
__mtx_lock_sleep() at __mtx_lock_sleep+0x438
__mtx_lock_flags() at __mtx_lock_flags+0x124
chn_intr() at chn_intr+0x30
bcmchan_trigger() at bcmchan_trigger+0x38
chn_trigger() at chn_trigger+0xd4
vchan_trigger() at vchan_trigger+0x10c
chn_trigger() at chn_trigger+0xd4
chn_write() at chn_write+0x12c
dsp_io_ops() at dsp_io_ops+0x148
dsp_write() at dsp_write+0x38
devfs_write_f() at devfs_write_f+0x114
dofilewrite() at dofilewrite+0x84
kern_writev() at kern_writev+0x5c
sys_write() at sys_write+0xc8
do_el0_sync() at do_el0_sync+0x608
handle_el0_sync() at handle_el0_sync+0x6c
--- exception, esr 0x56000000
KDB: enter: panic
[ thread pid 3696 tid 101505 ]
Stopped at      kdb_enter+0x48: str     xzr, [x19, #976]
db> bt
Tracing pid 3696 tid 101505 td 0xffff0000e3010c80
db_trace_self() at db_trace_self
db_stack_trace() at db_stack_trace+0xf8
db_command() at db_command+0x390
db_command_loop() at db_command_loop+0x58
db_trap() at db_trap+0x10c
kdb_trap() at kdb_trap+0x364
handle_el1h_sync() at handle_el1h_sync+0x18
--- exception, esr 0xf2000000
kdb_enter() at kdb_enter+0x48
vpanic() at vpanic+0x208
panic() at panic+0x48
__mtx_lock_sleep() at __mtx_lock_sleep+0x438
__mtx_lock_flags() at __mtx_lock_flags+0x124
chn_intr() at chn_intr+0x30
bcmchan_trigger() at bcmchan_trigger+0x38
chn_trigger() at chn_trigger+0xd4
vchan_trigger() at vchan_trigger+0x10c
chn_trigger() at chn_trigger+0xd4
chn_write() at chn_write+0x12c
dsp_io_ops() at dsp_io_ops+0x148
dsp_write() at dsp_write+0x38
devfs_write_f() at devfs_write_f+0x114
dofilewrite() at dofilewrite+0x84
kern_writev() at kern_writev+0x5c
sys_write() at sys_write+0xc8
do_el0_sync() at do_el0_sync+0x608
handle_el0_sync() at handle_el0_sync+0x6c
--- exception, esr 0x56000000
db> 


> > There isn't even any random noise as the Pi4 reboots.
> > RasPiOS makes a little noise during reboot on a Pi5 during reboot.
> 
> Those crackling noises you get when the pi boots are only audible through the audio jack. Seem to recall reading it was something to do with the DAC they use.

Not a crackling sound on the Pi5, more like the "thump" emitted by early AC coupled amps. 

That's for pointing out the Pi4 has an audio out jack, I'd forgotten!
During reboot there was considerable noise through the speakers, hissing
and a few thumps came out during reboot, silence during fsck and after
return to multi-user

Thanks for writing!

bob prohaska