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Subject: Re: [Phishing Risk] [External] Re: Does it make sense to create a
 centralized fan control module?
To: John Wang <wangzhiqiang.bj@bytedance.com>
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From: Heyi Guo <guoheyi@linux.alibaba.com>
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Date: Wed, 16 Jun 2021 19:03:49 +0800
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Cc: Zhikui Ren <zhikui.ren@intel.com>,
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 <openbmc-bounces+openbmc=archiver.kernel.org@lists.ozlabs.org>

Hi John,

Thanks for your reply. Please see my comments inline.

On 2021/6/16 上午10:49, John Wang wrote:
> On Wed, Jun 16, 2021 at 10:02 AM Heyi Guo <guoheyi@linux.alibaba.com> wrote:
>> Hi All,
>>
>> Any comments for my questions at the top of this thread?
>>
>> Thanks,
>>
>> Heyi
>>
>>
>> On 2021/6/11 上午9:23, Heyi Guo wrote:
>>> Please ignore my early emails; only this one is the final version. I
>>> must have misused some shortcut key to send the unfinished versions
>>> while I wanted to save it locally...
>>>
>>> Sorry for the noise.
>>>
>>> Heyi
>>>
>>> On 2021/6/11 上午9:14, Heyi Guo wrote:
>>>> Hi All,
>>>>
>>>> Right now fan related data like tacho and PWM is fetched in
>>>> dbus-sensors, and published to d-bus as sensor data, while fan
>>>> control is made in another module like pid-control, which can fetch
>>>> data and set value via d-bus.
>>>>
>>>> In some common sense, we may think about putting all fan related work
>>>> into one single module (which may be based on pid-control), i.e. it
>>>> can read tacho and PWM from hardware directly, calculate the required
> As I understand it, if you just want to bypass dbus and read pwm/tach
> directly you can refer to this.
> https://github.com/openbmc/openbmc/blob/master/meta-quanta/meta-gsj/recipes-phosphor/fans/phosphor-pid-control/config-2ssd.json#L6-L7

Do you suggest to use sysfs interface to access pwm/tach? However, we 
are using a I2C centralized fan controller and we don't have 
corresponding kernel driver for it. We propose to access this device by 
using /dev/i2c-<bus> interface directly in user mode.


>
>>>> PWM by some algorithm like PID, and then write to PWM hardware
>>>> directly; the data will also be published to d-bus for other modules
>>>> to consume, like fansensor from dbus-sensors.
>>>>
>>>> Does it make sense to do that? Or is there any reason for the current
>>>> design?
> I don't know why it's designed this way, but are you experiencing any problems?
Not really.
> According to our past experience, pid-control reads/writes pwm/tach
> quite smoothly,
> but pid-control has some trouble reading the temperature of some
> sensors via dbus.(eg psusensors).
> That's another topic...

As I mentioned above, there is no sysfs interface for fan pwm/tach on 
our platform. We can only rely on dbus interfaces if using the upstream 
phosphor-pid-control. Then we think about centralizing all fan related 
hardware access into one module (like pid-control), but not sure if 
there's any problem for this idea.

Thanks,

Heyi

>
>>>> I'm new to OpenBMC and some of my understanding may be totally wrong.
>>>>
>>>> Looking forward to your expert advice.
>>>>
>>>> Thanks,
>>>>
>>>> Heyi