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Subject: Re: [v4 07/11] dt-bindings: hwmon: Add documents for PECI hwmon
 client drivers
From:   Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
To:     Rob Herring <robh@kernel.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Haiyue Wang <haiyue.wang@linux.intel.com>,
        Vernon Mauery <vernon.mauery@linux.intel.com>,
        James Feist <james.feist@linux.intel.com>,
        devicetree@vger.kernel.org,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Jeffery <andrew@aj.id.au>,
        Arnd Bergmann <arnd@arndb.de>,
        Jason M Biils <jason.m.bills@linux.intel.com>,
        Joel Stanley <joel@jms.id.au>
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 <a05b44a2-ecc8-b028-4308-47d88523a6f1@linux.intel.com>
 <CAL_JsqJ8rjRzaqasjbdq-jkYfWxdo72YnmKAVNxDwo6wtyv1xg@mail.gmail.com>
 <51752610-d2c1-7fbc-101e-e99346fa29e4@linux.intel.com>
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Message-ID: <8b56c103-fdab-fc98-f4d8-9bf435a9b59b@linux.intel.com>
Date:   Wed, 23 May 2018 14:56:43 -0700
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On 5/23/2018 1:03 PM, Jae Hyun Yoo wrote:
> On 5/23/2018 12:33 PM, Rob Herring wrote:
>> On Wed, May 23, 2018 at 11:37 AM, Jae Hyun Yoo
>> <jae.hyun.yoo@linux.intel.com> wrote:
>>> On 5/23/2018 8:11 AM, Rob Herring wrote:
>>>>
>>>> On Tue, May 22, 2018 at 12:18 PM, Jae Hyun Yoo
>>>> <jae.hyun.yoo@linux.intel.com> wrote:
>>>>>
>>>>> On 5/22/2018 9:42 AM, Rob Herring wrote:
>>>>>>
>>>>>>
>>>>>> On Mon, May 21, 2018 at 12:59:05PM -0700, Jae Hyun Yoo wrote:
>>>>>>>
>>>>>>>
>>>>>>> This commit adds dt-bindings documents for PECI hwmon client 
>>>>>>> drivers.
>>>>>>>
>>>>>>> Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
>>>>>>> Reviewed-by: Haiyue Wang <haiyue.wang@linux.intel.com>
>>>>>>> Reviewed-by: James Feist <james.feist@linux.intel.com>
>>>>>>> Reviewed-by: Vernon Mauery <vernon.mauery@linux.intel.com>
>>>>>>> Cc: Andrew Jeffery <andrew@aj.id.au>
>>>>>>> Cc: Arnd Bergmann <arnd@arndb.de>
>>>>>>> Cc: Jason M Biils <jason.m.bills@linux.intel.com>
>>>>>>> Cc: Joel Stanley <joel@jms.id.au>
>>>>>>> ---
>>>>>>>     .../bindings/hwmon/peci-cputemp.txt           | 23
>>>>>>> ++++++++++++++++++
>>>>>>>     .../bindings/hwmon/peci-dimmtemp.txt          | 24
>>>>>>> +++++++++++++++++++
>>>>>>>     2 files changed, 47 insertions(+)
>>>>>>>     create mode 100644
>>>>>>> Documentation/devicetree/bindings/hwmon/peci-cputemp.txt
>>>>>>>     create mode 100644
>>>>>>> Documentation/devicetree/bindings/hwmon/peci-dimmtemp.txt
>>>>>>>
>>>>>>> diff --git 
>>>>>>> a/Documentation/devicetree/bindings/hwmon/peci-cputemp.txt
>>>>>>> b/Documentation/devicetree/bindings/hwmon/peci-cputemp.txt
>>>>>>> new file mode 100644
>>>>>>> index 000000000000..2f59aee12d9e
>>>>>>> --- /dev/null
>>>>>>> +++ b/Documentation/devicetree/bindings/hwmon/peci-cputemp.txt
>>>>>>> @@ -0,0 +1,23 @@
>>>>>>> +Bindings for Intel PECI (Platform Environment Control Interface)
>>>>>>> cputemp
>>>>>>> driver.
>>>>>>> +
>>>>>>> +Required properties:
>>>>>>> +- compatible : Should be "intel,peci-cputemp".
>>>>>>> +- reg        : Should contain address of a client CPU. Address 
>>>>>>> range
>>>>>>> of
>>>>>>> CPU
>>>>>>> +              clients is starting from 0x30 based on PECI
>>>>>>> specification.
>>>>>>> +
>>>>>>> +Example:
>>>>>>> +       peci-bus@0 {
>>>>>>> +               #address-cells = <1>;
>>>>>>> +               #size-cells = <0>;
>>>>>>> +               < more properties >
>>>>>>> +
>>>>>>> +               peci-cputemp@30 {
>>>>>>> +                       compatible = "intel,peci-cputemp";
>>>>>>> +                       reg = <0x30>;
>>>>>>> +               };
>>>>>>
>>>>>>
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>>> +               peci-dimmtemp@30 {
>>>>>>> +                       compatible = "intel,peci-dimmtemp";
>>>>>>> +                       reg = <0x30>;
>>>>>>> +               };
>>>>>>
>>>>>>
>>>>>>
>>>>>> As I said in the prior version, 2 nodes at the same address is wrong.
>>>>>>
>>>>>> Rob
>>>>>>
>>>>>
>>>>> In PECI bus, there is one and only bus host (adapter) and multiple
>>>>> clients on a PECI bus, and PECI spec doesn't allow multiple 
>>>>> originators
>>>>> so only the host device can originate message.
>>>>
>>>>
>>>> Yes, I get that. A single host still has to address slave devices.
>>>>
>>>>> In this implementation,
>>>>> all message transactions on a bus from client driver modules and user
>>>>> space will be serialized well in the PECI core bus driver so bus
>>>>> occupation and traffic arbitration will be managed well in the PECI 
>>>>> core
>>>>> bus driver even in case of a bus has 2 client drivers at the same
>>>>> address. I'm sure that this implementation doesn't make that kind of
>>>>> problem to OS.
>>>>
>>>>
>>>> Multiple clients to a single device is common, but that is a software
>>>> problem and doesn't belong in DT.
>>>>
>>>> I don't think there is a single other case in the kernel where
>>>> multiple drivers can bind to the same device at a given bus address.
>>>> That is why we have things like MFD. Though in this case, why can't
>>>> one hwmon driver register multiple hwmon devices (cpu and dimm temps)?
>>>>
>>>
>>> It was implemented as a single driver until v2 but dimm temps need
>>> delayed creation unlikely the cpu temps on hwmon subsystem because of
>>> memory training behavior of remote x86 cpus. Since hwmon doesn't allow
>>> incremental creation, I had to divide it into two, cputemp and dimmtemp,
>>> so that cputemp can be registered immediately when the remote x86 cpu
>>> turns on and dimmtemp can be registered by delayed creation. It is the
>>> reason why I had to make the two hwmon driver modules that sharing a
>>> single device address.
>>
>> That all sounds like kernel problems to me. Stop designing your DT
>> binding around what the kernel can or can't *currently* support.
>>
>>> Additionally, PECI isn't limited for temperature
>>> monitoring feature but it can be used for other functions such as
>>> platform management, cpu interface tuning and diagnostics and failure
>>> analysis, so in case of adding a new driver for the functions, we should
>>> add an another DT node which is sharing the same cpu address.
>>
>> No, the driver should add support for those additional functions.
>> Perhaps you will need to use MFD.
>>
> 
> Do you mean that the device address sharing is acceptable if I make
> these nodes under "simple-mfd"?
> 
> Thanks,
> 
> -Jae

Hi Rob,

I'm planning to change the whole PECI node like below:

peci: peci@1e78b000 {
	compatible = "simple-bus";
	#address-cells = <1>;
	#size-cells = <1>;
	ranges = <0x0 0x1e78b000 0x60>;

	peci0: peci-bus@0 {
		compatible = "aspeed,ast2500-peci";
		reg = <0x0 0x60>;
		#address-cells = <1>;
		#size-cells = <0>;
		interrupts = <15>;
		clocks = <&syscon ASPEED_CLK_GATE_REFCLK>;
		resets = <&syscon ASPEED_RESET_PECI>;
		clock-frequency = <24000000>;
		msg-timing = <1>;
		addr-timing = <1>;
		rd-sampling-point = <8>;
		cmd-timeout-ms = <1000>;
		status = "disabled";

		peci-client@30 {
			compatible = "simple-mfd", "syscon";
			reg = <0x30>;

			cputemp: cputemp {
				compatible = "intel,peci-cputemp";
			};

			dimmtemp: dimmtemp {
				compatible = "intel,peci-dimmtemp";
			};
		};

		peci-client@31 {
			compatible = "simple-mfd", "syscon";
			reg = <0x31>;

			cputemp: cputemp {
				compatible = "intel,peci-cputemp";
			};

			dimmtemp: dimmtemp {
				compatible = "intel,peci-dimmtemp";
			};
		};
	};
};

Can you please check whether it is acceptable or not?

Thanks,

-Jae