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

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Date:   Tue, 19 Nov 2019 13:49:53 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     eberman@...eaurora.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

Quoting eberman@...eaurora.org (2019-11-15 17:29:03)
> 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.

So there will be a patch before this that makes
__qcom_scm_is_call_available use SMCCC? I still don't get how it won't
be recursive but I'll have to wait until v3 I guess.

> 
> >> +       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
> 

Ok. I'd prefer a WARN_ON() instead but it's not really up to me. At
least mention this in the commit text.