Re: [PATCH] fsl-imx: Add simple RTC emulation for i.MX6 and i.MX7 boards

[Philippe Mathieu-Daudé]

Hi Peter,

On 12/12/23 15:18, Peter Maydell wrote:
> On Sun, 12 Nov 2023 at 09:22, Nikita Ostrenkov <n.ostrenkov@gmail.com> wrote:
>
> Hi; thanks for this patch, and sorry I haven't got round
> to reviewing it earlier.
>
> > Signed-off-by: Nikita Ostrenkov <n.ostrenkov@gmail.com>
> > ---
> >   hw/misc/imx7_snvs.c         | 59 ++++++++++++++++++++++++++++++++-----
> >   hw/misc/trace-events        |  4 +--
> >   include/hw/misc/imx7_snvs.h | 14 ++++++++-
> >   3 files changed, 67 insertions(+), 10 deletions(-)


> > @@ -31,6 +33,16 @@ struct IMX7SNVSState {
> >       SysBusDevice parent_obj;
> >
> >       MemoryRegion mmio;
> > +
> > +    /*
> > +     * Needed to preserve the tick_count across migration, even if the
> > +     * absolute value of the rtc_clock is different on the source and
> > +     * destination.
> > +     */
> > +    int64_t tick_offset_vmstate;
>
> You don't need tick_offset_vmstate -- it is only in the p031
> RTC device as a backwards-compatibility thing for older versions
> of QEMU. Migrating tick_offset alone is sufficient in a new
> device. (It seems to have been unfortunately copied-and-pasted
> into the goldfish RTC device; we should probably fix that bug.)
>
> > +    int64_t tick_offset;
> > +
> > +    uint64_t lpcr;
>
> We've now added state to this device, which means that it needs
> a VMState structure to handle migration, and it needs a reset
> function.

I just noticed your v1 review after reviewing v2. Indeed
'tick_offset' need to be migrated. Now about reset(), RTC
are somehow different. When resetting a machine in the same
QEMU process I'd expect the RTC offset to not be reset.

Could this be clarified by adding a reset handler with no
code but a comment /* RTC state is usually kept by CMOS
battery and is not reset */ maybe?

> >   };
> >
> >   #endif /* IMX7_SNVS_H */
> > --
>
> thanks
> -- PMM