linux-kernel - Re: [PATCH v2] irqchip/gicv3: Workaround for NVIDIA erratum T241-FABRIC-4

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Message-ID: <bf9f8763f0116c3f05c008923edfbedb@kernel.org>
Date:   Thu, 16 Mar 2023 16:00:04 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Shanker Donthineni <sdonthineni@...dia.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vikram Sethi <vsethi@...dia.com>,
        Thierry Reding <treding@...dia.com>
Subject: Re: [PATCH v2] irqchip/gicv3: Workaround for NVIDIA erratum
 T241-FABRIC-4

On 2023-03-16 15:10, Sudeep Holla wrote:
> On Wed, Mar 15, 2023 at 07:27:14AM -0500, Shanker Donthineni wrote:
>> Hi Marc,
>> 
>> On 3/15/23 03:34, Marc Zyngier wrote:
>> > Please don't duplicate existing code. There is already the required
>> > infrastructure in drivers/firmware/smccc/soc_id.c. All you need to do
>> > is:
>> >
>> > - disassociate the SMCCC probing from the device registration
>> >
>> > - probe the SOC_ID early
>> >
>> > - add accessors for the relevant data
>> >
>> > - select ARM_SMCCC_SOD_ID/ARM_SMCCC_DISCOVERY from the GICv3 Kconfig
>> 
>> 
>> I have not modified soc_id.c as it expects to be loaded as a module 
>> with
>> the use of module_init() and module_exit() functions. The exported 
>> symbols
>> in soc_id driver cannot be accessed from the built-in code.
>> 
>> Agree, the SOD-ID discovery code was duplicated.
>> 
>> Please guide me if the below approach is okay?
>> 
>> 1) Probe the SOC-ID in arm_smccc_version_init() and export two 
>> functions
>> arm_smccc_get_soc_id_version() and arm_smccc_get_soc_id_revision().
>> 
>> --- a/drivers/firmware/smccc/smccc.c
>> +++ b/drivers/firmware/smccc/smccc.c
>> @@ -17,9 +17,13 @@ static enum arm_smccc_conduit smccc_conduit = 
>> SMCCC_CONDUIT_NONE;
>> 
>>  bool __ro_after_init smccc_trng_available = false;
>>  u64 __ro_after_init smccc_has_sve_hint = false;
>> +s32 __ro_after_init smccc_soc_id_version = SMCCC_RET_NOT_SUPPORTED;
>> +s32 __ro_after_init smccc_soc_id_revision = SMCCC_RET_NOT_SUPPORTED;
>> 
>>  void __init arm_smccc_version_init(u32 version, enum 
>> arm_smccc_conduit conduit)
>>  {
>> +       struct arm_smccc_res res;
>> +
>>         smccc_version = version;
>>         smccc_conduit = conduit;
>> 
>> @@ -27,6 +31,18 @@ void __init arm_smccc_version_init(u32 version, 
>> enum arm_smccc_conduit conduit)
>>         if (IS_ENABLED(CONFIG_ARM64_SVE) &&
>>             smccc_version >= ARM_SMCCC_VERSION_1_3)
>>                 smccc_has_sve_hint = true;
>> +
>> +       if ((smccc_version >= ARM_SMCCC_VERSION_1_2) &&
>> +           (smccc_conduit != SMCCC_CONDUIT_NONE)) {
>> +               arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
>> +                                    ARM_SMCCC_ARCH_SOC_ID, &res);
>> +               if ((s32)res.a0 >= 0) {
>> +                       arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_SOC_ID, 0, 
>> &res);
>> +                       smccc_soc_id_version = (s32)res.a0;
>> +                       arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_SOC_ID, 1, 
>> &res);
>> +                       smccc_soc_id_revision = (s32)res.a0;
>> +               }
>> +       }
>>  }
>> 
>> 
>> +s32 arm_smccc_get_soc_id_version(void)
>> +{
>> +       return smccc_soc_id_version;
>> +}
>> +EXPORT_SYMBOL_GPL(arm_smccc_get_soc_id_version);
>> +
>> +s32 arm_smccc_get_soc_id_revision(void)
>> +{
>> +       return smccc_soc_id_revision;
>> +}
>> +EXPORT_SYMBOL_GPL(arm_smccc_get_soc_id_revision);
>> 
>> 
> 
> Overall, it looks OK to me. However I see neither the gic nor the 
> soc_id
> can be build as module atm. So do we really need the export symbols if 
> no
> other modules are using it ?

It really shouldn't be exported. Having accessors should be enough.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...