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

[Eric Blake <eblake@redhat.com>]

On 06/29/2018 03:19 AM, Peter Maydell wrote:
> On 25 June 2018 at 14:12, Gerd Hoffmann <kraxel@redhat.com> 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