linux-kernel - Re: [PATCH v1 2/3] drivers/perf: add DesignWare PCIe PMU driver

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Message-ID: <ae249149-a17f-7652-729b-262a977080a5@arm.com>
Date:   Mon, 26 Sep 2022 15:32:47 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Bjorn Helgaas <helgaas@...nel.org>
Cc:     will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, rdunlap@...radead.org,
        mark.rutland@....com, baolin.wang@...ux.alibaba.com,
        zhuo.song@...ux.alibaba.com, linux-pci@...r.kernel.org
Subject: Re: [PATCH v1 2/3] drivers/perf: add DesignWare PCIe PMU driver

On 2022-09-26 14:31, Shuai Xue wrote:
> + Bjorn Helgaas
> 
> 在 2022/9/23 PM11:54, Jonathan Cameron 写道:
>>
>>>
>>>>    
>>>>> +#define RP_NUM_MAX				32 /* 2die * 4RC * 4Ctrol */
>>>>
>>>> This driver is 'almost' generic. So if you an avoid defines based on a particular
>>>> platform that's definitely good!
>>>
>>> Good idea. How about defining RP_NUM_MAX as 64? As fars as I know,
>>> some platfrom use 2 sockets, 2 die per socket.
>>> Then 2 sockets * 2 dies * 4 Root Complex * 4 root port.
>>
>> Setting a reasonable maximum is fine - but make sure the code then fails with
>> a suitable error message if there are more!
> 
> OK, I will add a discovery logic here and count PMU number at runtime.
> 
>>
>>
>>>>> +#define DWC_PCIE_LANE_SHIFT			4
>>>>> +#define DWC_PCIE_LANE_MASK			GENMASK(9, 4)
>>>>> +
>>>>> +#define DWC_PCIE_EVENT_CNT_CTRL			0x8
>>>>> +#define DWC_PCIE__CNT_EVENT_SELECT_SHIFT	16
>>>>
>>>> Why double __?  If point is , then
>>>> naming works better
>>>> DWC_PCIE_EVENT_CNT_CTRL_REG
>>>> DWC_PCIE_EVENT_CNT_CTRL_EV_SELECT_MSK etc
>>>
>>> Yes, I point to use double `__` to indicate it is a field of register,
>>> as CMN and CCN drivers do. I also considered naming with REG explicitly,
>>> but the macro is so long that I often have to wrap code into multilines.
>>> Any way, it's fine to rename if you still suggest to do so.
>>
>> I don't particularly mind.  This convention was new to me.
> 
> Haha, then I will leave the double `__` as CMN and CCN drivers do.

FWIW I'm not sure there's really any convention. CCN seems to use 
double-underscores as distinct separators in a consistent 
CCN_REG_NAME__FIELD_NAME__SUFFIX pattern. Conversely in CMN I used it as 
an indication of the usual CMN_REG_NAME_FIELD_NAME_VALUE pattern being 
abbreviated where it would have been uncomfortably long otherwise (and 
particularly where the field name reflects the register name anyway); it 
just seemed like a good visual cue to imply that something was missing.

Robin.