Re: [PATCH] hw/audio/lm4549: Don't try to open a zero-frequency audio voice

[Peter Maydell <peter.maydell@linaro.org>]

On Sat, 8 Nov 2025 at 00:22, BALATON Zoltan <balaton@eik.bme.hu> wrote:
>
> On Fri, 7 Nov 2025, Peter Maydell wrote:
> > If the guest incorrectly programs the lm4549 audio chip with a zero
> > frequency, we will pass this to AUD_open_out(), which will complain:
> >
> >   A bug was just triggered in AUD_open_out
> >   Save all your work and restart without audio
> >   I am sorry
> >   Context:
> >   audio: frequency=0 nchannels=2 fmt=S16 endianness=little
> >
> > The datasheet doesn't say what we should do here, only that the valid
> > range for the freqency is 8000 to 48000 Hz; we choose to log the
> > guest error and ignore an attempt to change the DAC rate to something
> > outside the valid range.
> >
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/410
> > Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> > ---
> > This bug has been around for so long and is a weird edge case whose
> > only effect is to print a debug message, so it doesn't really seem
> > worth cc'ing stable on.
> > ---
> > hw/audio/lm4549.c | 17 ++++++++++++++++-
> > 1 file changed, 16 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/audio/lm4549.c b/hw/audio/lm4549.c
> > index 745441bd790..bf711c49c04 100644
> > --- a/hw/audio/lm4549.c
> > +++ b/hw/audio/lm4549.c
> > @@ -15,6 +15,7 @@
> >
> > #include "qemu/osdep.h"
> > #include "hw/hw.h"
> > +#include "qemu/log.h"
> > #include "qemu/audio.h"
> > #include "lm4549.h"
> > #include "migration/vmstate.h"
> > @@ -179,9 +180,23 @@ void lm4549_write(lm4549_state *s,
> >         break;
> >
> >     case LM4549_PCM_Front_DAC_Rate:
> > -        regfile[LM4549_PCM_Front_DAC_Rate] = value;
> >         DPRINTF("DAC rate change = %i\n", value);
> >
> > +        /*
> > +         * Valid sample rates are 4kHz to 48kHz.
>
> Commit message says minimum is 8kHz. One of these is likely incorrect.
> Maybe a typo in commit message?

Whoops; yes, you're right, the commit message is the one
that's wrong. The datasheet for this is at
https://www.ti.com/lit/ds/symlink/lm4549b.pdf
and it says 4kHz.

-- PMM