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

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Message-ID: <58316fc3-1ee1-b530-e783-ccd8225e07d6@linaro.org>
Date:   Fri, 24 Mar 2023 09:56:15 +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 23/03/2023 14:45, Souradeep Chowdhury wrote:
> 
> 
> On 3/22/2023 8:23 PM, Krzysztof Kozlowski wrote:
>> 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?
> 
> This has no dependency on other resources except that it parses some 
> information from DT nodes, so deferred probe handling is not needed
> in this case.

Yes, I know, but if we would ever add it how this driver can handle it?
This is antipattern.

Best regards,
Krzysztof