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From:   Rob Herring <robh@kernel.org>
Date:   Thu, 24 May 2018 08:47:43 -0500
Message-ID: <CAL_JsqK0HRi1meN=Y8jxRHrvrBwH_bZj3WVcYwy9MS0ZBJt0gw@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 Wed, May 23, 2018 at 4:56 PM, Jae Hyun Yoo
<jae.hyun.yoo@linux.intel.com> wrote:
> 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";

These compatibles alone is not correct. There should be a specific
compatible for the device.

Also, I don't think "syscon" even makes sense in this case.

>                         reg = <0x30>;
>
>                         cputemp: cputemp {
>                                 compatible = "intel,peci-cputemp";
>                         };

There is no point in this node being in DT. It doesn't define any
resources. All it does is provide you a convenient way to bind your
driver, but that is not the purpose of DT. Put a specific compatible
in the parent and its driver can instantiate whatever child devices it
wants.

Rob