Re: [PATCH v5 3/4] firmware: psci: Read and use vendor reset types

[Lorenzo Pieralisi <lpieralisi@kernel.org>]

On Mon, Aug 12, 2024 at 11:46:08PM +0530, Shivendra Pratap wrote:
> 
> 
> On 8/9/2024 10:28 PM, Elliot Berman wrote:
> > On Fri, Aug 09, 2024 at 03:30:38PM +0200, Lorenzo Pieralisi wrote:
> >> On Wed, Aug 07, 2024 at 11:10:50AM -0700, Elliot Berman wrote:
> >>
> >> [...]
> >>
> >>>>> +static void psci_vendor_sys_reset2(unsigned long action, void *data)
> >>>>
> >>>> 'action' is unused and therefore it is not really needed.
> >>>>
> >>>>> +{
> >>>>> +	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);
> >>>>> +		}
> >>>>> +	}
> >>>>> +}
> >>>>> +
> >>>>>  static int psci_sys_reset(struct notifier_block *nb, unsigned long action,
> >>>>>  			  void *data)
> >>>>>  {
> >>>>> +	if (data && num_psci_reset_params)
> >>>>
> >>>> So, reboot_mode here is basically ignored; if there is a vendor defined
> >>>> reset, we fire it off.
> >>>>
> >>>> I think Mark mentioned his concerns earlier related to REBOOT_* mode and
> >>>> reset type (granted, the context was different):
> >>>>
> >>>> https://lore.kernel.org/all/20200320120105.GA36658@C02TD0UTHF1T.local/
> >>>>
> >>>> I would like to understand if this is the right thing to do before
> >>>> accepting this patchset.
> >>>>
> >>>
> >>> I don't have any concerns to move this part below checking reboot_mode.
> >>> Or, I could add reboot_mode == REBOOT_COLD check.
> >>
> >> The question is how can we map vendor specific reboot magic to Linux
> >> reboot modes sensibly in generic PSCI code - that's by definition
> >> vendor specific.
> >>
> > 
> > I don't think it's a reasonable thing to do. "reboot bootloader" or
> > "reboot edl" don't make sense to the Linux reboot modes.
> > 
> > I believe the Linux reboot modes enum is oriented to perspective of
> > Linux itself and the vendor resets are oriented towards behavior of the
> > SoC.
> > 
> > Thanks,
> > Elliot
> > 
> 
> Agree.
> 
> from perspective of linux reboot modes, kernel's current implementation in reset path is like:
> __
> #1 If reboot_mode is WARM/SOFT and PSCI_SYSRESET2 is supported 
>     Call PSCI - SYSTEM_RESET2 - ARCH RESET
> #2 ELSE
>     Call PSCI - SYSTEM_RESET COLD RESET
> ___
> 
> ARM SPECS for PSCI SYSTEM_RESET2
> This function extends SYSTEM_RESET. It provides:
> • ARCH RESET: set Bit[31] to 0               = > This is already in place in condition #1.
> • vendor-specific resets: set Bit[31] to 1.  = > current patchset adds this part before kernel's reboot_mode reset at #0.
> 
> 
> In current patchset, we see a condition added at #0-psci_vendor_reset2 being called before kernel’s current reboot_mode condition and it can take any action only if all below conditions are satisfied.
> - PSCI SYSTEM_RESET2 is supported.
> - psci dt node defines an entry "bootloader" as a reboot-modes.
> - User issues reboot with a command say - (reboot bootloader).
> - If vendor reset fails, default reboot mode will execute as is.
> 
> Don't see if we will skip or break the kernel reboot_mode flow with this patch. 
> Also if user issues reboot <cmd> and <cmd> is supported on SOC vendor reset psci node, should cmd take precedence over kernel reboot mode enum? may be yes? 
> 

Please wrap lines when replying.

I don't think it is a matter of precedence. reboot_mode and the reboot
command passed to the reboot() syscall are there for different (?)
reasons.

What I am asking is whether it is always safe to execute a PSCI vendor
reset irrispective of the reboot_mode value.

Lorenzo