Re: [PATCH v2 3/4] watchdog: add meson secure watchdog driver

[Guenter Roeck]

On 10/21/19 1:03 AM, Xingyu Chen wrote:
> Hi, Guenter
>
> On 2019/10/21 0:56, Guenter Roeck wrote:
> > On 10/18/19 1:33 AM, Xingyu Chen wrote:
> > > The watchdog controller on the Meson-A/C series SoCs is moved to secure
> > > world, watchdog operation needs to be done in secure EL3 mode via ATF,
> > > Non-secure world can call SMC instruction to trap to AFT for watchdog
> > > operation.
> > >
> > > Signed-off-by: Xingyu Chen <xingyu.chen@xxxxxxxxxxx>
> > > ---
> > > Â drivers/watchdog/KconfigÂÂÂÂÂÂÂÂ |Â 17 ++++
> > > Â drivers/watchdog/MakefileÂÂÂÂÂÂÂ |ÂÂ 1 +
> > > Â drivers/watchdog/meson_sec_wdt.c | 187 +++++++++++++++++++++++++++++++++++++++
> > > Â 3 files changed, 205 insertions(+)
> > > Â create mode 100644 drivers/watchdog/meson_sec_wdt.c
> > >
> > > diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> > > index 58e7c10..e84be42 100644
> > > --- a/drivers/watchdog/Kconfig
> > > +++ b/drivers/watchdog/Kconfig
> > > @@ -826,6 +826,23 @@ config MESON_GXBB_WATCHDOG
> > > ÂÂÂÂÂÂÂ To compile this driver as a module, choose M here: the
> > > ÂÂÂÂÂÂÂ module will be called meson_gxbb_wdt.
> > > +config MESON_SEC_WATCHDOG
> > > +ÂÂÂ tristate "Amlogic Meson Secure watchdog support"
> > > +ÂÂÂ depends on MESON_SM
> > > +ÂÂÂ depends on ARCH_MESON || COMPILE_TEST
> >
> > This dependency is pointless. MESON_SM already depends on ARCH_MESON,
> > thus specifying "COMPILE_TEST" here adds no value but only
> > creates confusion.
> Thanks for your analysis, perhaps i should remove the line below.
> - depends on ARCH_MESON || COMPILE_TEST
>
> Is it ok to modify code above like this ?

Yes.
[ ... ]

> > > +static unsigned int meson_sec_wdt_get_timeleft(struct watchdog_device *wdt_dev)
> > > +{
> > > +ÂÂÂ int ret;
> > > +ÂÂÂ unsigned int timeleft;
> > > +ÂÂÂ struct meson_sec_wdt *data = watchdog_get_drvdata(wdt_dev);
> > > +
> > > +ÂÂÂ ret = meson_sm_call(data->fw, SM_WATCHDOG_OPS, &timeleft,
> > > +ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ MESON_SIP_WDT_GETTIMELEFT, 0, 0, 0, 0);
> > > +
> > > +ÂÂÂ if (ret)
> > > +ÂÂÂÂÂÂÂ return ret;
> >
> > Meh, that doesn't work. I just realized that the return type is unsigned,
> > so returning a negative error code is pointless. Guess we'll have to
> > live with returning 0 in this case after all. I wonder if we should
> > fix the API and return an integer (with negative error code), but that
> > is a different question.
> Thanks for your review.
>
> IMO, if returning an integer, and the value which copy to user buf should be formatted with %d instead of %u (see timeleft_show), it will cause the max value of timeleft is reduced from 4294967295 to 2147483647. but i'am not sure whether it will bring risk.

Not that it matters right now, but I don't think that limiting 'timeleft'
reporting to 2147483647 seconds, or ~68 years, would cause any risk.
It would just be a large patch changing several drivers all at once,
that is all.

> So i also think returning 0 may be better in this case.

Yes, please do that.

Thanks,
Guenter