Re: [Qemu-devel] [PULL 1/6] audio/hda: create millisecond timers that handle IO

[Eric Blake]

On 06/29/2018 03:19 AM, Peter Maydell wrote:
> On 25 June 2018 at 14:12, Gerd Hoffmann <address@hidden> wrote:
> > Currently, the HDA device tries to sync itself with the QEMU audio
> > backend by waiting for the guest driver to handle buffer completion
> > interrupts. This causes the backend to often read too much data from the
> > device, as well as running out of data whenever the guest takes too long
> > to handle the interrupt.
> >
> > According to the HDA specification, the guest is also not required to
> > use interrupts, but can also sync itself by polling the LPIB registers.
> >
> > This patch will introduce high frequency (1000Hz) timers that interface
> > with the device and allow for much smoother emulation of the LPIB
> > registers. Since the timing is now provided by these timers, the need
> > to wait for buffer completion interrupts also ceases.
>
> > +static inline int64_t hda_bytes_per_second(HDAAudioStream *st)
> > +{
> > +    return 2 * st->as.nchannels * st->as.freq;
> > +}
>
> Hi; Coverity warns about this expression because the
> multiplication is done as a 32-bit multiply and the
> result is returned as a 64-bit (CID 1393631). As usual,
> a suitable cast would fix it.

Said suitable cast might look best written without parentheses, as in:

return 2LL * st->as.nchannels * st->as.freq;

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org