linux-kernel - Re: [PATCH] drivers/perf: hisi: Add identifier sysfs file

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Message-ID: <086e0fd0-590b-8a95-5ac9-9d585e8a3342@huawei.com>
Date:   Thu, 18 Jun 2020 10:18:42 +0100
From:   John Garry <john.garry@...wei.com>
To:     Shaokun Zhang <zhangshaokun@...ilicon.com>, <will@...nel.org>,
        <mark.rutland@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <qiangqing.zhang@....com>,
        <jolsa@...hat.com>, <linuxarm@...wei.com>
Subject: Re: [PATCH] drivers/perf: hisi: Add identifier sysfs file

On 18/06/2020 02:40, Shaokun Zhang wrote:
>> }
>>   
>> +	hha_pmu->identifier = readl(hha_pmu->base + HHA_VERSION);
> Since we are now refactoring the PMU framework, the PMU version offset
> is always the same except DDRC PMU and other uncore PMU modules will
> also use this, how about we do it as the common code:
> 
> #define HISI_PMU_VERSION_REG   0x1CF0
> int hisi_uncore_pmu_version(struct hisi_pmu *hisi_pmu)
> {
>         return readl(hisi_pmu->base + HISI_PMU_VERSION_REG);
> }
> EXPORT_SYMBOL_GPL(hisi_uncore_pmu_version);

Hi Shaokun,

Some points to make:

- It's hardly worth having a separate function to do this 1-line readl() 
call, especially since it not even generic (DDRC is different)

- We would have to export it (or put in a common header file with static 
inline keywords) - less exports are good

- with factoring out common code, it's good to reduce total code - this 
change would increase it, AFAICS

- This is HW specific. The driver is currently layered such that all HW 
specific stuff is in the HW driver (like hisi_uncore_ddrc_pmu.c), and 
not library code (hisi_uncore_pmu.c). I don't see why you want to mix 
that, like you're proposing in the framework revision you proposed 
internally.

Thanks,
John

> 
> hha_pmu->identifier = hisi_uncore_pmu_version(hha_pmu);
> we can remove the duplicated PMU version register definition in each module.
> 
> Thanks,
> Shaokun
> 
>> +
>>   	return 0;
>>   }
>>   
>> @@ -320,10 +323,23 @@ static const struct attribute_group hisi_hha_pmu_cpumask_attr_group = {
>>   	.attrs = hisi_hha_pmu_cpumask_attrs,
>>   };