linux-kernel - Re: [PATCH 6/6] firmware: qcom_scm: Only compile legacy calls on ARM

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Date:   Sun, 7 Mar 2021 11:42:45 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Andy Gross <agross@...nel.org>,
        Elliot Berman <eberman@...eaurora.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Brian Masney <masneyb@...tation.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH 6/6] firmware: qcom_scm: Only compile legacy calls on ARM

On Sat 06 Mar 00:18 CST 2021, Stephen Boyd wrote:

> Quoting Elliot Berman (2021-03-05 10:18:09)
> > On 3/3/2021 10:14 PM, Stephen Boyd wrote:
> > > Quoting Elliot Berman (2021-03-03 19:35:08)
> > >>
> > >> On 2/23/2021 1:45 PM, Stephen Boyd wrote:
> > >>> These scm calls are never used outside of legacy ARMv7 based platforms.
> > >>> That's because PSCI, mandated on arm64, implements them for modern SoCs
> > >>> via the PSCI spec. Let's move them to the legacy file and only compile
> > >>> the legacy file into the kernel when CONFIG_ARM=y. Otherwise provide
> > >>> stubs and fail the calls. This saves a little bit of space in an
> > >>> arm64 allmodconfig >
> > >>>    $ ./scripts/bloat-o-meter vmlinux.before vmlinux.after
> > >>>    add/remove: 0/8 grow/shrink: 5/7 up/down: 509/-4405 (-3896)
> > >>>    Function                                     old     new   delta
> > >>>    __qcom_scm_set_dload_mode.constprop          312     452    +140
> > >>>    qcom_scm_qsmmu500_wait_safe_toggle           288     416    +128
> > >>>    qcom_scm_io_writel                           288     408    +120
> > >>>    qcom_scm_io_readl                            376     492    +116
> > >>>    __param_str_download_mode                     23      28      +5
> > >>>    __warned                                    4327    4326      -1
> > >>>    qcom_iommu_init                              272     268      -4
> > >>>    e843419@...f_00010432_324                      8       -      -8
> > >>>    qcom_scm_call                                228     208     -20
> > >>>    CSWTCH                                      5925    5877     -48
> > >>>    _sub_I_65535_1                            163100  163040     -60
> > >>>    _sub_D_65535_0                            163100  163040     -60
> > >>>    qcom_scm_wb                                   64       -     -64
> > >>>    qcom_scm_lock                                320     160    -160
> > >>>    qcom_scm_call_atomic                         212       -    -212
> > >>>    qcom_scm_cpu_power_down                      308       -    -308
> > >>>    scm_legacy_call_atomic                       520       -    -520
> > >>>    qcom_scm_set_warm_boot_addr                  720       -    -720
> > >>>    qcom_scm_set_cold_boot_addr                  728       -    -728
> > >>>    scm_legacy_call                             1492       -   -1492
> > >>>    Total: Before=66737642, After=66733746, chg -0.01%
> > >>>
> > >>> Commit 9a434cee773a ("firmware: qcom_scm: Dynamically support SMCCC and
> > >>> legacy conventions") didn't mention any motivating factors for keeping
> > >>> the legacy code around on arm64 kernels, i.e. presumably that commit
> > >>> wasn't trying to support these legacy APIs on arm64 kernels.
> > >>
> > >> There are arm targets which support SMCCC convention and use some of
> > >> these removed functions. Can these functions be kept in qcom-scm.c and
> > >> wrapped with #if IS_ENABLED(CONFIG_ARM)?
> > >>
> > > 
> > > It can be wrapped in qcom-scm.c, but why? It's all the same object file
> > > so I'm lost why it matters. I suppose it would make it so the struct
> > > doesn't have to be moved around and declared in the header? Any other
> > > reason? I moved it to the legacy file so that it was very obvious that
> > > the API wasn't to be used except for "legacy" platforms that don't use
> > > PSCI.
> > > 
> > 
> > There are "legacy" arm platforms that use the SMCCC (scm_smc_call) and 
> > use the qcom_scm_set_{warm,cold}_boot_addr and qcom_scm_cpu_power_down 
> > functions.
> 
> Ah ok. Weird, but I get it. Amazing that SMCCC was adopted there but
> PSCI wasn't!
> 
> > 
> >  > +    desc.args[0] = flags;
> >  > +    desc.args[1] = virt_to_phys(entry);
> >  > +
> >  > +    return scm_legacy_call_atomic(NULL, &desc, NULL);
> >  > +}
> >  > +EXPORT_SYMBOL(qcom_scm_set_cold_boot_addr);
> > 
> > This should still be qcom_scm_call.
> 
> You mean s/scm_legacy_call_atomic/qcom_scm_call/ right?
> 
> I don't really want to resend the rest of the patches if this last one
> is the only one that needs an update. This was a semi-RFC anyway so
> maybe it's fine if the first 5 patches get merged and then I can resend
> this one? Otherwise I will resend this again next week or so with less
> diff for this patch.

I'm fine with merging the first 5, but was hoping that Elliot could
provide either a "Reviewed-by" or at least an "Acked-by" on these.

Regards,
Bjorn