linux-kernel - Re: [PATCH V1 3/4] soc: qcom: boot_stat: Add Driver Support for Boot Stats

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Message-ID: <7b939818-993a-e849-e7e0-ae9ea74ea52b@linaro.org>
Date:   Wed, 22 Mar 2023 15:53:21 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
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 V1 3/4] soc: qcom: boot_stat: Add Driver Support for Boot
 Stats

On 22/03/2023 14:54, Souradeep Chowdhury wrote:
> 
> 
> On 3/21/2023 11:07 PM, Krzysztof Kozlowski wrote:
>> On 21/03/2023 14:51, 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 print the information. This information is
>>> useful in verifying if the existing boot KPIs have regre
>>
>>
>>> +/**
>>> + *  struct boot_stats - timestamp information related to boot stats
>>> + *  @bootloader_start:	Time for the starting point of the abl bootloader
>>> + *  @bootloader_end:	Time when the kernel starts loading from abl bootloader
>>> + */
>>> +struct boot_stats {
>>> +	u32 bootloader_start;
>>> +	u32 bootloader_end;
>>> +} __packed;
>>> +
>>> +static struct boot_stats __iomem *boot_stats;
>>> +static void __iomem *mpm_counter_base;
>>> +static u32 mpm_counter_freq;
>>
>> No file-scope variables. Does not scale, not easy for review and
>> maintenance. Avoid such code.
> 
> Ack
>>
>>> +
>>> +static int mpm_parse_dt(void)
>>> +{
>>> +	struct device_node *np_imem, *np_mpm2;
>>> +
>>> +	np_imem = of_find_compatible_node(NULL, NULL,
>>> +					  "qcom,imem-boot_stats");
>>> +	if (!np_imem) {
>>> +		pr_err("can't find qcom,imem node\n");
>>
>> So you are printing errors everywhere, on every soc and with compile
>> test on every platform there is in the world... sorry, it does not work
>> like that.
> 
> Ack
>>
>>> +		return -ENODEV;
>>> +	}
>>> +	boot_stats = of_iomap(np_imem, 0);
>>> +	if (!boot_stats) {
>>> +		pr_err("boot_stats: Can't map imem\n");
>>> +		goto err1;
>>> +	}
>>
>>
>>> +
>>> +static void __exit boot_stats_exit(void)
>>> +{
>>> +}
>>> +module_exit(boot_stats_exit)
>>
>>
>> I don't think this is some special code which deserves init calls. Make
>> it module_platform_driver().
> 
> Since this just reads some values from the Imem region and prints it to 
> the user and doesn't have a specific device associated with it, a 

Which is not really an argument for such antipattern, but okay...

> generic module code is written for it and not a module_platform_driver().

... so how do you handle deferred probe?

Best regards,
Krzysztof