linux-kernel - Re: [PATCH v3 04/10] Documentations: dt-bindings: Add a document of PECI adapter driver for Aspeed AST24xx/25xx SoCs

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Date:   Wed, 18 Apr 2018 09:45:56 -0700
From:   Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Alan Cox <alan@...ux.intel.com>, Andrew Jeffery <andrew@...id.au>,
        Andrew Lunn <andrew@...n.ch>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Fengguang Wu <fengguang.wu@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Haiyue Wang <haiyue.wang@...ux.intel.com>,
        James Feist <james.feist@...ux.intel.com>,
        Jason M Biils <jason.m.bills@...ux.intel.com>,
        Jean Delvare <jdelvare@...e.com>,
        Joel Stanley <joel@....id.au>,
        Julia Cartwright <juliac@....teric.us>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Milton Miller II <miltonm@...ibm.com>,
        Pavel Machek <pavel@....cz>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stef van Os <stef.van.os@...drive-technologies.com>,
        Sumeet R Pawnikar <sumeet.r.pawnikar@...el.com>,
        Vernon Mauery <vernon.mauery@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org, devicetree@...r.kernel.org,
        Linux HWMON List <linux-hwmon@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        OpenBMC Maillist <openbmc@...ts.ozlabs.org>
Subject: Re: [PATCH v3 04/10] Documentations: dt-bindings: Add a document of
 PECI adapter driver for Aspeed AST24xx/25xx SoCs

On 4/18/2018 6:59 AM, Rob Herring wrote:
> On Tue, Apr 17, 2018 at 5:06 PM, Jae Hyun Yoo
> <jae.hyun.yoo@...ux.intel.com> wrote:
>> On 4/17/2018 11:16 AM, Jae Hyun Yoo wrote:
>>>
>>> On 4/17/2018 6:16 AM, Rob Herring wrote:
>>>>
>>>> On Mon, Apr 16, 2018 at 6:12 PM, Jae Hyun Yoo
>>>> <jae.hyun.yoo@...ux.intel.com> wrote:
>>>>>
>>>>> On 4/16/2018 11:10 AM, Rob Herring wrote:
>>>>>>
>>>>>>
>>>>>> On Tue, Apr 10, 2018 at 11:32:06AM -0700, Jae Hyun Yoo wrote:
>>>>>>>
>>>>>>>
>>>>>>> This commit adds a dt-bindings document of PECI adapter driver for
>>>>>>> Aspeed
>>>>>>> AST24xx/25xx SoCs.
>>>>
>>>>
>>>> [...]
>>>>
>>>>>>> +- clocks            : Should contain clock source for PECI
>>>>>>> controller.
>>>>>>> +                     Should reference clkin.
>>>>>>> +- clock_frequency   : Should contain the operation frequency of PECI
>>>>>>> controller
>>>>>>> +                     in units of Hz.
>>>>>>> +                     187500 ~ 24000000
>>>>>>
>>>>>>
>>>>>>
>>>>>> This is the frequency of the bus or used to derive it? It would be
>>>>>> better to specify the bus frequency instead and have the driver
>>>>>> calculate its internal freq. And then use "bus-frequency" instead.
>>>>>>
>>>>>
>>>>> I agree with you. Actually, it is being used for operation frequency
>>>>> setting
>>>>> of PECI controller module in SoC so it's different from the meaning of
>>>>> "bus-frequency". I'll change it to "operation-frequency".
>>>>
>>>>
>>>> No, now you've gone from a standard property name to something custom.
>>>> Why do you need to set the frequency in DT if it is not related to the
>>>> interface frequency?
>>>>
>>>> Rob
>>>>
>>>
>>> Actually, the interface frequency is affected by the operation frequency
>>> but there is no description of its relationship in datasheet. I'll check
>>> again about the detail to ASPEED chip vendor and will use
>>> 'bus-frequency' if available.
>>>
>>
>> I investigated it more deeply. Basically, by the spec, PECI bus speed
>> cannot be set as a fixed speed. A PECI bus can have a wide speed range
>> from 2Kbps to 2Mbps which is dynamically set by a handshaking sequence
>> between an originator and clients called 'timing negotiation' in spec.
>> This timing negotiation behavior happens on every single transaction so the
>> bus speed also can vary on every transactions. So I'm thinking a custom
>> property name for it, 'peci-clk-frequency' if it is acceptable.
> 
> Okay, seems bus-frequency is not appropriate here. So use
> 'clock-frequency' (note the '-' not '_' as that is the standard
> property).
> 
> Rob
> 

Thanks! I'll use 'clock-frequency' for it.

Jae