linux-kernel - Re: [PATCH V1 RESEND 1/3] perf/imx_ddr: Add system PMU identifier for userspace

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Date:   Thu, 28 May 2020 09:35:13 +0800
From:   Shaokun Zhang <zhangshaokun@...ilicon.com>
To:     John Garry <john.garry@...wei.com>, Will Deacon <will@...nel.org>,
        "Rob Herring" <robh@...nel.org>
CC:     Mark Rutland <mark.rutland@....com>, <devicetree@...r.kernel.org>,
        "Joakim Zhang" <qiangqing.zhang@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        NXP Linux Team <linux-imx@....com>,
        Shawn Guo <shawnguo@...nel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V1 RESEND 1/3] perf/imx_ddr: Add system PMU identifier for
 userspace

Hi,

On 2020/5/27 22:34, John Garry wrote:
>>>>>
>>>>> I also really dislike this. What's the preferred way to identify the SoC
>>>>> from userspace?
>>>>
>>>> /proc/cpuinfo? ;)
>>>
>>> The *SoC*!
>>>
>>>> For an non-firmware specific case, I'd say soc_device should be. I'd
>>>> guess ACPI systems don't use it and for them it's dmidecode typically.
>>>> The other problem I have with soc_device is it is optional.
>>>
>>
>> Hi Will,
>>
>>> John -- what do you think about using soc_device to expose this information,
>>> with ACPI systems using DMI data instead?
>>
>> Generally I don't think that DMI is reliable, and I saw this as the least preferred choice. I'm looking at the sysfs DMI info for my dev board, and I don't even see anything like a SoC identifier.
>>
>> As for the event_source device sysfs identifier file, it would not always contain effectively the same as the SoC ID.
>>
>> Certain PMUs which I'm interested in plan to have probe-able identification info available in future.
>>
> 
> BTW, Shaokun now tells me that the HiSi uncore PMU HW have such registers to identify the implementation. I didn't know.
> 

Right, we have this register which shows the PMU version.

Thanks,
Shaokun


> So we could add that identifier file for those PMUs as proof-of-concept, exposing that register.
> 
> As for other PMUs which I'm interested in, again, future versions should have such registers to self-identify.
> 
> So using something derived from the DT compat string would hopefully be the uncommon case.
> 
> Cheers,
> John
> 
> .
>