linux-kernel - Re: [PATCH v2 10/18] firmware: qcom_scm-64: Improve SMC convention detection

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Date:   Fri, 15 Nov 2019 17:29:03 -0800
From:   eberman@...eaurora.org
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org,
        saiprakash.ranjan@...eaurora.org, tsoni@...eaurora.org,
        sidgup@...eaurora.org, psodagud@...eaurora.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 10/18] firmware: qcom_scm-64: Improve SMC convention
 detection

On 2019-11-15 16:21, Stephen Boyd wrote:
> Quoting Elliot Berman (2019-11-12 13:22:46)
>> diff --git a/drivers/firmware/qcom_scm-64.c 
>> b/drivers/firmware/qcom_scm-64.c
>> index 977654bb..b82b450 100644
>> --- a/drivers/firmware/qcom_scm-64.c
>> +++ b/drivers/firmware/qcom_scm-64.c
>> @@ -302,21 +302,20 @@ int __qcom_scm_hdcp_req(struct device *dev, 
>> struct qcom_scm_hdcp_req *req,
>> 
>>  void __qcom_scm_init(void)
>>  {
>> -       u64 cmd;
>> -       struct arm_smccc_res res;
>> -       u32 function = SMCCC_FUNCNUM(QCOM_SCM_SVC_INFO, 
>> QCOM_SCM_INFO_IS_CALL_AVAIL);
>> -
>> -       /* First try a SMC64 call */
>> -       cmd = ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL, 
>> ARM_SMCCC_SMC_64,
>> -                                ARM_SMCCC_OWNER_SIP, function);
>> -
>> -       arm_smccc_smc(cmd, QCOM_SCM_ARGS(1), cmd & 
>> (~BIT(ARM_SMCCC_TYPE_SHIFT)),
>> -                     0, 0, 0, 0, 0, &res);
>> -
>> -       if (!res.a0 && res.a1)
>> -               qcom_smccc_convention = ARM_SMCCC_SMC_64;
>> -       else
>> -               qcom_smccc_convention = ARM_SMCCC_SMC_32;
>> +       qcom_smccc_convention = ARM_SMCCC_SMC_64;
>> +       if (__qcom_scm_is_call_available(NULL, QCOM_SCM_SVC_INFO,
>> +                       QCOM_SCM_INFO_IS_CALL_AVAIL) == 1)
> 
> Is this asking if the "is call available function" is available by 
> using
> the is call available function? That is recursive. Isn't that why we
> make a manually open coded SMC call to see if it works? If this isn't
> going to work we may want to just have a property in DT that tells us
> what to do.

Yes. The reason the open coded SMC call was made was because a fast call
works better here. __qcom_scm_is_call_available uses standard call, and
I'll address this in v3.

>> +       BUG();
> 
> This BUG() is new and not mentioned in the commit text. Why can't we
> just start failing all scm calls if we can't detect the calling
> convention?

Bjorn has requested that the BUG was introduced in v1:
https://lore.kernel.org/patchwork/patch/1148619/#1350062


>> +out:
>> +       pr_debug("QCOM SCM SMC Convention: %llu\n", 
>> qcom_smccc_convention);
> 
> Maybe pr_info() is more appropriate. PSCI currently prints out the
> version info so maybe printing something like "QCOM SCM SMC_64 calling
> convention" will be useful for early debugging.

Sure, will do.

Thanks,

Elliot

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