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

[Florian Fainelli <florian.fainelli@broadcom.com>]

On 11/15/24 05:35, 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 ?
> 
> Are these "reset types" exported to user space ?

AFAICT, they are not, but arguably you already need custom user space 
which is capable of doing:

syscall(SYS_reboot, LINUX_REBOOT_MAGIC1, LINUX_REBOOT_MAGIC2, 
LINUX_REBOOT_CMD_RESTART2, reboot_cmd);

in order to utilize the custom reboot mode. I could imagine that with a 
discovery mechanism, a wrapper could be written to check that the 
specified command is actually supported before issuing the system call, 
or even have the system call do that under the hood.

I don't personally feel like this is very important in the sense that as 
long as a fallback exists for an unsupported reboot command specified, 
the system does reboot.
-- 
Florian