Re: [Qemu-devel] [PATCH] rtc: placing RTC memory region outside BQL

["Gonglei (Arei)" <arei.gonglei@huawei.com>]

> -----Original Message-----
> From: Peter Maydell [mailto:peter.maydell@linaro.org]
> Sent: Tuesday, February 06, 2018 5:49 PM
> To: Gonglei (Arei)
> Cc: Paolo Bonzini; QEMU Developers; Huangweidong (C)
> Subject: Re: [Qemu-devel] [PATCH] rtc: placing RTC memory region outside BQL
> 
> On 6 February 2018 at 08:24, Gonglei (Arei) <arei.gonglei@huawei.com>
> wrote:
> > So, taking BQL is necessary, and what we can do is trying our best to narrow
> > down the process of locking ? For example, do the following wrapping:
> >
> > static void rtc_rasie_irq(RTCState *s)
> > {
> >     qemu_mutex_lock_iothread();
> >     qemu_irq_raise(s->irq);
> >     qemu_mutex_unlock_iothread();
> > }
> >
> > static void rtc_lower_irq(RTCState *s)
> > {
> >     qemu_mutex_lock_iothread();
> >     qemu_irq_lower(s->irq);
> >     qemu_mutex_unlock_iothread();
> > }
> 
> If you do that you'll also need to be careful about not calling
> those functions from contexts where you already hold the iothread
> mutex (eg timer callbacks), since you can't lock a mutex you
> already have locked.
> 
Exactly, all contexts caused by the main process. :)
Three timers callbacks, calling rtc_reset().

Thanks,
-Gonglei