linux-kernel - Re: [PATCH v2] firmware: qcom_scm: Only compile legacy calls on ARM

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Date:   Wed, 31 Mar 2021 18:26:32 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Elliot Berman <eberman@...eaurora.org>,
        Brian Masney <masneyb@...tation.org>,
        Stephan Gerhold <stephan@...hold.net>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>
Subject: Re: [PATCH v2] firmware: qcom_scm: Only compile legacy calls on ARM

Quoting Stephen Boyd (2021-03-23 15:43:36)
> 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: 5/6 up/down: 509/-4401 (-3892)
>  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
>  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=66737606, After=66733714, 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.
> 
> Cc: Elliot Berman <eberman@...eaurora.org>
> Cc: Brian Masney <masneyb@...tation.org>
> Cc: Stephan Gerhold <stephan@...hold.net>
> Cc: Jeffrey Hugo <jhugo@...eaurora.org>
> Cc: Douglas Anderson <dianders@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
> 

Elliot, can you ack/review this?

> Followup to v1 (https://lore.kernel.org/r/20210223214539.1336155-7-swboyd@chromium.org):
>  * Don't change the legacy file to use legacy calls only
>  * Wrap more things in CONFIG_ARM checks
>