linux-kernel - Re: [PATCH V4 2/3] soc: qcom: boot_stat: Add Driver Support for Boot Stats

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Message-ID: <35ac64ab-512d-1425-7a1b-6e8d3806c8a8@linaro.org>
Date:   Thu, 4 May 2023 19:19:18 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Souradeep Chowdhury <quic_schowdhu@...cinc.com>,
        Caleb Connolly <caleb.connolly@...aro.org>,
        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 V4 2/3] soc: qcom: boot_stat: Add Driver Support for Boot
 Stats

On 04/05/2023 09:35, Souradeep Chowdhury wrote:
> 
> 
> On 5/4/2023 4:23 AM, Caleb Connolly wrote:
>>
>>
>> On 17/04/2023 16:08, 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/146aa6b0.boot_stats # cat abl_time
>>> 17898 ms
>>> /sys/kernel/debug/146aa6b0.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>
>>
>> Hi,
>>
>> [...]
>>> +
>>> +static int boot_stats_probe(struct platform_device *pdev)
>>> +{
>>> +    struct device *bootstat_dev = &pdev->dev;
>>> +    struct bs_data *drvdata;
>>> +
>>> +    drvdata = devm_kzalloc(bootstat_dev, sizeof(*drvdata), GFP_KERNEL);
>>> +    platform_set_drvdata(pdev, drvdata);
>>> +
>>> +    drvdata->dbg_dir = debugfs_create_dir(dev_name(bootstat_dev), 
>>> NULL);
>>
>> This might be better as just "qcom_boot_stats", rather than including
>> the address.
> 
> We usually use the dev_name to represent the one to one correspondence 

Who is "we"?

> of the debugfs file with the device. Will create the root dir as
> "qcom_boot_stats" and push the dev_name dir inside it.

No, this doesn't sound logical. Please use just the "qcom_boot_stats" as 
Caleb suggested.

> 
>>
>> [...]
>>> +
>>> +static const struct of_device_id boot_stats_dt_match[] = {
>>> +    { .compatible = "qcom,sm8450-bootstats" },
>>
>> This driver doesn't only support sm8450, I've tested this on sdm845 and
>> it works just fine. Can we use a generic compatible here instead?
> 
> We can add soc specific compatibles here to extend support for other 
> socs. This also captures the SoCs for which the driver is supported 
> which won't be the case if we use a generic compatible.

No. If there is no difference between SoCs, please don't add 
soc-specific compatibles. They pollute the kernel and provide no 
additional benefits. Please use generic compatible and add 
platform-specific ones only if you have something to override.

> 
> 
>>> +    { }
>>> +};
>>> +MODULE_DEVICE_TABLE(of, boot_stats_dt_match);
>>> +
>>> +static struct platform_driver boot_stat_driver = {
>>> +    .probe  = boot_stats_probe,
>>> +    .remove_new = boot_stats_remove,
>>> +    .driver = {
>>> +        .name = "qcom-boot-stats",
>>> +        .of_match_table = boot_stats_dt_match,
>>> +    },
>>> +};
>>> +module_platform_driver(boot_stat_driver);
>>> +
>>> +MODULE_DESCRIPTION("Qualcomm Technologies Inc. Boot Stat driver");
>>> +MODULE_LICENSE("GPL");
>>> -- 
>>> 2.7.4
>>>
>>

-- 
With best wishes
Dmitry