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

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Fri, Nov 15, 2024 at 11:08:22AM -0800, Elliot Berman wrote:
> On Fri, Nov 15, 2024 at 02:35:52PM +0100, Lorenzo Pieralisi wrote:
> > On Wed, Oct 23, 2024 at 09:30:21AM -0700, Elliot Berman wrote:
> > > 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
> > > > > @@ -29,6 +29,8 @@
> > > > >  #include <asm/smp_plat.h>
> > > > >  #include <asm/suspend.h>
> > > > >
> > > > > +#define REBOOT_PREFIX "mode-"
> > > > 
> > > > Maybe move this near the function that uses it.
> > > > 
> > > > > +
> > > > >  /*
> > > > >   * While a 64-bit OS can make calls with SMC32 calling conventions, for some
> > > > >   * calls it is necessary to use SMC64 to pass or return 64-bit values.
> > > > > @@ -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.
> > 
> > Well, that's one of the doubts I have about enabling this code. From
> > userspace we are requesting a reboot (I don't even think that user
> > space knows which reboot modes are actually implemented (?)) and we may
> > end up issuing one with completely different semantics ?
> 
> You're right here, userspace issue a "reboot bootloader" and if kernel
> doesn't have the support to set up the right cookie, the device would do
> a normal reboot and not stop at the bootloader. This problem exists
> today and I think whether this is an issue to solve is out of scope here.

That's true. It is the same issue we have with reboot_mode anyway.

Is it a fair statement to say that currently when we request a reboot,
the reboot mode is the one set through /sys/kernel/reboot/mode ?

Does user space use that file today ?

I guess userspace does not take specific actions according to the
reset it thinks it issues - it is a question.

> > Are these "reset types" exported to user space ?
> > 
> 
> No mechanism exists to do that. We could do something specific for PSCI
> or do something generic for everybody. I don't think something specific
> for PSCI is the right approach because it's a general problem. I don't
> think there's enough interest to change reboot command plumbing to
> advertise valid reset types to userspace.

That's for sure. I suppose the most important bit is making sure that
all resets comply with the kernel semantics expected from a *reset*;
I appreciate that's a vague statement (and I have no idea how to enforce
it) but that's the gist of this discussion.

Another thing I am worried about is device drivers restart handlers
(ie having to parse a command that might be platform specific in a
generic driver to grok what reset was actually issued and what action
should be taken).

I admit it is a tough nut to crack this one - apologies for the time
it is taking to reach an agreement.

Lorenzo