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

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Date:   Thu, 23 Mar 2023 19:15:54 +0530
From:   Souradeep Chowdhury <quic_schowdhu@...cinc.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...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 V1 3/4] soc: qcom: boot_stat: Add Driver Support for Boot
 Stats



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.

> 
> Best regards,
> Krzysztof
>