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

Stephen Boyd
2019-11-19T21:49:58Z

Quoting eberman@codeaurora.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.