Re: [PATCH] firmware: smccc: Fix Arm SMCCC SOC_ID name call

[Andre Przywara <andre.przywara@arm.com>]

Hi Paul,

many thanks for the answer, and apologies for the delay (was on holidays).

On 5/1/26 22:14, Paul Benoit wrote:
> On 4/30/2026 10:59 AM, Andre Przywara wrote:
>> [You don't often get email from andre.przywara@arm.com. Learn why this 
>> is important at https://aka.ms/LearnAboutSenderIdentification ]
>>
>> Hi Paul,
>>
>> is there any update on this?
>> One more thought below ...
>>
> 
> Hi Andre,
> 
> Using the incorrect SMC32 vs. the correct SMC64 interface, for SOC_ID
> Name, was addressed by Ampere firmware some months back.
> 
> In addition to recent firmware now responding to a SMC64 CC SOC_ID Name
> request, it will continue to respond to an incorrect/broken SMC32
> request and return the SOC_ID Name string packed in 64-bit registers.
> This will allow Linux kernels 6.15+, incorrectly using SMC32 to get the
> SOC_ID Name, to continue to work with new Ampere firmware versions.

OK, many thanks for the information, that seems to be a good solution.

> In other words, unless any other vendors also implemented SOC_ID Name as
> SMC32 in their firmware, I think we can let the Ampere firmware handle
> the SMC32 vs. SMC64 mix-up and keep the handling of it out of the Linux
> kernel.

But I think availability of the machines predates the "some month back" 
period you mention above?
So it would only work if users would update the firmware?

> It should now be safe to make the SMC32->SMC64 SOC_ID Name change in
> Linux.

So I wonder if would still need a quirk for AmpereOne. I guess we can't 
query the TF-A build version easily, and a DMI quirk probably doesn't 
work either, judging by the dmidecode output of one machine I looked at.
So I was wondering if we should employ the following algorithm:

	- do call with 64-bit FID
	- if (ret == -1) && (soc_id == jep106:0a16:0004)
		- try 32-bit FID

Would that work? That checks for the SoC, not the firmware version, but 
seems way easier to implement and would cover all cases.

Thoughts?

Cheers,
Andre

> 
> 
>> On 9/4/25 16:29, Sudeep Holla wrote:
>>> On Wed, Sep 03, 2025 at 05:38:44PM -0400, Paul Benoit wrote:
>>>> On 9/3/2025 10:49 AM, Sudeep Holla wrote:
>>>>> On Wed, Sep 03, 2025 at 03:23:58PM +0100, Sudeep Holla wrote:
>>>>>> On Tue, Sep 02, 2025 at 06:20:53PM +0100, Andre Przywara wrote:
>>>>>>> Commit 5f9c23abc477 ("firmware: smccc: Support optional Arm SMCCC 
>>>>>>> SOC_ID
>>>>>>> name") introduced the SOC_ID name string call, which reports a human
>>>>>>> readable string describing the SoC, as returned by firmware.
>>>>>>> The SMCCC spec v1.6 describes this feature as AArch64 only, since 
>>>>>>> we rely
>>>>>>> on 8 characters to be transmitted per register. Consequently the 
>>>>>>> SMCCC
>>>>>>> call must use the AArch64 calling convention, which requires bit 
>>>>>>> 30 of
>>>>>>> the FID to be set. The spec is a bit confusing here, since it 
>>>>>>> mentions
>>>>>>> that in the parameter description ("2: SoC name (optionally 
>>>>>>> implemented for
>>>>>>> SMC64 calls, ..."), but still prints the FID explicitly as 
>>>>>>> 0x80000002.
>>>>>>> But as this FID is using the SMC32 calling convention (correct 
>>>>>>> for the
>>>>>>> other two calls), it will not match what mainline TF-A is 
>>>>>>> expecting, so
>>>>>>> any call would return NOT_SUPPORTED.
>>>>>>>
>>>>>>
>>>>>> Good catch and I must admit I completely missed it inspite of 
>>>>>> discussing
>>>>>> 32b vs 64b FID around the same time this was introduced.
>>>>>>
>>>>>>> Add a 64-bit version of the ARCH_SOC_ID FID macro, and use that 
>>>>>>> for the
>>>>>>> SoC name version of the call.
>>>>>>>
>>>>>>> Fixes: 5f9c23abc477 ("firmware: smccc: Support optional Arm SMCCC 
>>>>>>> SOC_ID name")
>>>>>>> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>>>>>>> ---
>>>>>>> Hi,
>>>>>>>
>>>>>>> as somewhat expected, this now fails on an Ampere machine, which
>>>>>>> reported a string in /sys/devices/soc0/machine before, but is now 
>>>>>>> missing
>>>>>>> this file.
>>>>>>> Any idea what's the best way to handle this? Let the code try the 
>>>>>>> 32-bit
>>>>>>> FID, when the 64-bit one fails? Or handle this as some kind of 
>>>>>>> erratum?
>>>>>>>
>>>>>>
>>>>>> Not sure about it yet. Erratum seems good option so that we can avoid
>>>>>> others getting it wrong too as they might just run the kernel and 
>>>>>> be happy
>>>>>> if the machine sysfs shows up as we decided to do fallback to 32b 
>>>>>> FID.
>>>>>>
>>>>>> I will start a discussion to get the spec updated and pushed out 
>>>>>> and see
>>>>>> how that goes.
>>>>>>
>>>>>> The change itself looks good and happy to get it merged once we know
>>>>>> what is the best approach(erratum vs fallback).
>>>>>>
>>>>>
>>>>> Looking at the SMCCC spec(DEN0028 v1.6 G Edition) ->
>>>>> Section 7.4.6 Implementation responsibilities
>>>>>
>>>>> If implemented, the firmware:
>>>>> ...
>>>>> • must not implement SoC_ID_type == 2 for SMC32.
>>>>> • can optionally implement SoC_ID_type == 2 for SMC64 (Function ID 
>>>>> 0xC000_0002),
>>>>> ...
>>>>>
>>>>> So Ampere is not spec conformant here and hence I prefer to handle 
>>>>> it as
>>>>> erratum. Hopefully we can use SOC_ID version and revision to keep 
>>>>> the scope
>>>>> of erratum confined to smallest set of platforms.
>>>>>
>>>>> Paul,
>>>>>
>>>>> Thoughts ?
>>>>>
>>>>
>>>> Am I correctly understanding that, if the SMC64 SOC_ID Name call fails,
>>>> rather than an unconditional fallback to the SMC32 call, the SMC32
>>>> fallback would only be occurring under the proposed erratum?
>>>>
>>>
>>> Correct, if we have unconditional fallback to the SMC32 call, then there
>>> is a chance that this issue gets carried into newer Ampere systems as 
>>> f/w
>>> gets copied as well as other vendors will also not notice the issue if
>>> they make similar mistake as the kernel silent makes a SMC32 call.
>>>
>>> We do need details of  the SoC revision and version for which we need to
>>> apply this workaround/erratum.
>>
>> So this looks more like a firmware erratum than a SoC specific one,
>> right? So I wonder if any SoC specific IDs are really appropriate here.
>> Is there some firmware version we can read via DMI or so to identify
>> affected systems?
>> Or shall we use a probably much easier SoC or even MIDR check anyway,
>> since it's just a fallback? As in: try smc64, if that fails and if it's
>> a core that ever shipped with that affected firmware, try smc32? I think
>> there is not much harm in trying those FIDs, so we just limit the scope
>> to Ampere cores - even though that's technically not the right method by
>> the book?
>>
>> Cheers,
>> Andre
>>
>>
>>
>>>
>>>> I brought this issue up at a weekly team meeting today, and I'll 
>>>> also be
>>>> communicating with the Ampere Computing firmware team regarding this
>>>> issue.
>>>
>>> Thanks!
>>>
>>
>