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

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Message-ID: <28c8bc92-4a55-8a07-1ece-333316d78410@quicinc.com>
Date: Mon, 12 Aug 2024 23:46:08 +0530
From: Shivendra Pratap <quic_spratap@...cinc.com>
To: Elliot Berman <quic_eberman@...cinc.com>,
        Lorenzo Pieralisi
	<lpieralisi@...nel.org>
CC: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Sebastian Reichel <sre@...nel.org>, Rob Herring
	<robh@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, Vinod Koul <vkoul@...nel.org>,
        Andy Yan
	<andy.yan@...k-chips.com>,
        Mark Rutland <mark.rutland@....com>,
        "Bartosz
 Golaszewski" <bartosz.golaszewski@...aro.org>,
        Satya Durga Srinivasu Prabhala
	<quic_satyap@...cinc.com>,
        Melody Olvera <quic_molvera@...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>,
        <quic_spratap@...inc.com>
Subject: Re: [PATCH v5 3/4] firmware: psci: Read and use vendor reset types



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?