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From:   Rob Herring <robh@kernel.org>
Date:   Wed, 23 May 2018 10:11:47 -0500
Message-ID: <CAL_JsqJ8rjRzaqasjbdq-jkYfWxdo72YnmKAVNxDwo6wtyv1xg@mail.gmail.com>
Subject: Re: [v4 07/11] dt-bindings: hwmon: Add documents for PECI hwmon
 client drivers
To:     Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
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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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)?

Rob