linux-kernel - Re: [PATCH V6 2/3] soc: qcom: boot_stat: Add Driver Support for Boot Stats

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Message-Id: <3faa9bf7-b42c-4951-8103-9ea2fe02eac1@app.fastmail.com>
Date:   Tue, 16 May 2023 10:19:38 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Souradeep Chowdhury" <quic_schowdhu@...cinc.com>,
        "Andy Gross" <agross@...nel.org>,
        "Konrad Dybcio" <konrad.dybcio@...ainline.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        "Bjorn Andersson" <andersson@...nel.org>,
        "Rob Herring" <robh+dt@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        "Sibi Sankar" <quic_sibis@...cinc.com>,
        "Rajendra Nayak" <quic_rjendra@...cinc.com>
Subject: Re: [PATCH V6 2/3] soc: qcom: boot_stat: Add Driver Support for Boot Stats

On Tue, May 9, 2023, at 12:52, Souradeep Chowdhury wrote:
> All of Qualcomm's proprietary Android boot-loaders capture boot time
> stats, like the time when the bootloader started execution and at what
> point the bootloader handed over control to the kernel etc. in the IMEM
> region. This information is captured in a specific format by this driver
> by mapping a structure to the IMEM memory region and then accessing the
> members of the structure to show the information within debugfs file.
> This information is useful in verifying if the existing boot KPIs have
> regressed or not. The information is shown in milliseconds, a sample
> log from sm8450(waipio) device is as follows:-
>
> /sys/kernel/debug/qcom_boot_stats # cat abl_time
> 17898 ms
> /sys/kernel/debug/qcom_boot_stats # cat pre_abl_time
> 2879 ms
>
> The Module Power Manager(MPM) sleep counter starts ticking at the PBL
> stage and the timestamp generated by the sleep counter is logged by
> the Qualcomm proprietary bootloader(ABL) at two points-> First when it
> starts execution which is logged here as "pre_abl_time" and the second
> when it is about to load the kernel logged as "abl_time". Documentation
> details are also added in Documentation/ABI/testing/debugfs-driver-bootstat
>
> Signed-off-by: Souradeep Chowdhury <quic_schowdhu@...cinc.com>
> ---
>  .../ABI/testing/debugfs-driver-bootstat       |  17 +++
>  drivers/soc/qcom/Kconfig                      |  10 ++
>  drivers/soc/qcom/Makefile                     |   1 +
>  drivers/soc/qcom/boot_stats.c                 | 100 ++++++++++++++++++

As mentioned in my reply to the binding, I don't think this should
be a driver at all. On top of that, even if it was a driver, it is
clearly not a "soc" driver since nothing in it has any relevance to
the hardware, rather than the first-stage loader, and drivers/soc/
drivers should never have their own user space interface either.

       Arnd