linux-kernel - Re: [PATCH v6 3/5] firmware: psci: Read and use vendor reset types

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Message-ID: <CAE-0n50s1gUt7jOWLEjDzi7ABVRLmAr1kG-6V6YjTZnPD2EMQw@mail.gmail.com>
Date: Wed, 23 Oct 2024 12:02:19 -0700
From: Stephen Boyd <swboyd@...omium.org>
To: Elliot Berman <quic_eberman@...cinc.com>
Cc: Andy Yan <andy.yan@...k-chips.com>, Arnd Bergmann <arnd@...db.de>, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, Bjorn Andersson <andersson@...nel.org>, 
	Catalin Marinas <catalin.marinas@....com>, Conor Dooley <conor+dt@...nel.org>, 
	Konrad Dybcio <konradybcio@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Olof Johansson <olof@...om.net>, Rob Herring <robh@...nel.org>, Sebastian Reichel <sre@...nel.org>, 
	Vinod Koul <vkoul@...nel.org>, Will Deacon <will@...nel.org>, cros-qcom-dts-watchers@...omium.org, 
	Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>, Melody Olvera <quic_molvera@...cinc.com>, 
	Shivendra Pratap <quic_spratap@...cinc.com>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Florian Fainelli <florian.fainelli@...adcom.com>, linux-pm@...r.kernel.org, 
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v6 3/5] firmware: psci: Read and use vendor reset types

Quoting Elliot Berman (2024-10-23 09:30:21)
> On Fri, Oct 18, 2024 at 10:42:46PM -0700, Stephen Boyd wrote:
> > Quoting Elliot Berman (2024-10-18 12:39:48)
> > > diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> > > index 2328ca58bba6..60bc285622ce 100644
> > > --- a/drivers/firmware/psci/psci.c
> > > +++ b/drivers/firmware/psci/psci.c
> > > @@ -305,9 +315,29 @@ static int get_set_conduit_method(const struct device_node *np)
> > >         return 0;
> > >  }
> > >
> > > +static void psci_vendor_sys_reset2(unsigned long action, void *data)
> > > +{
> > > +       const char *cmd = data;
> > > +       unsigned long ret;
> > > +       size_t i;
> > > +
> > > +       for (i = 0; i < num_psci_reset_params; i++) {
> > > +               if (!strcmp(psci_reset_params[i].mode, cmd)) {
> > > +                       ret = invoke_psci_fn(PSCI_FN_NATIVE(1_1, SYSTEM_RESET2),
> > > +                                            psci_reset_params[i].reset_type,
> > > +                                            psci_reset_params[i].cookie, 0);
> > > +                       pr_err("failed to perform reset \"%s\": %ld\n",
> > > +                               cmd, (long)ret);
> >
> > Do this intentionally return? Should it be some other function that's
> > __noreturn instead and a while (1) if the firmware returns back to the
> > kernel?
> >
>
> Yes, I think it's best to make sure we fall back to the architectural
> reset (whether it's the SYSTEM_RESET or architectural SYSTEM_RESET2)
> since device would reboot then.

Ok. Please add a comment in the code so we know that it's intentional.

>
> > > +               }
> > > +       }
> > > +}
> > > +
> > >  static int psci_sys_reset(struct notifier_block *nb, unsigned long action,
> > >                           void *data)
> > >  {
> > > +       if (data && num_psci_reset_params)
> > > +               psci_vendor_sys_reset2(action, data);
> > > +

I'd add a comment here as well indicating that a fallback is used.

> > >         if ((reboot_mode == REBOOT_WARM || reboot_mode == REBOOT_SOFT) &&
> > >             psci_system_reset2_supported) {
> > >                 /*
> > > @@ -750,6 +780,68 @@ static const struct of_device_id psci_of_match[] __initconst = {
> > >         {},
[...]
> > > +                       continue;
> > > +
> > > +               num = of_property_read_variable_u32_array(np, prop->name, magic, 1, 2);
> >
> > ARRAY_SIZE(magic)?
> >
> > > +               if (num < 0) {
> >
> > Should this be less than 1?
> >
>
> of_property_read_variable_u32_array should return -EOVERFLOW (or maybe
> -ENODATA) if the array is empty. I don't see it's possible for
> of_property_read_variable_u32_array() to return a non-negative value
> that's not 1 or 2.

I think you're saying a return value of 0 is impossible? Ok. I was
mostly looking at the usage of the return value later on in this patch
and trying to understand why 0 would be allowed as a possible return
value without looking at the details of
of_property_read_variable_u32_array(). I guess the 1, 2 are the min/max
though so it's fine.