linux-kernel - Re: [PATCH v3 2/7] bus: mhi: core: Introduce independent voting mechanism

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Date:   Wed, 20 May 2020 13:06:50 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     bbhatt@...eaurora.org
Cc:     manivannan.sadhasivam@...aro.org, linux-arm-msm@...r.kernel.org,
        hemantk@...eaurora.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/7] bus: mhi: core: Introduce independent voting
 mechanism

On 5/20/2020 12:43 PM, bbhatt@...eaurora.org wrote:
> On 2020-05-20 09:54, Jeffrey Hugo wrote:
>> On 5/18/2020 2:03 PM, Bhaumik Bhatt wrote:
>>> Allow independent votes from clients such that they can choose to vote
>>> for either the device or the bus or both. This helps in cases where the
>>> device supports autonomous low power mode wherein it can move to M2
>>> state without the need to notify the host. Clients can also vote only to
>>> keep the underlying bus active without having the device in M0 state to
>>> support offload use cases.
>>>
>>> Signed-off-by: Bhaumik Bhatt <bbhatt@...eaurora.org>
>>> ---
>>
>> I wonder, why doesn't this fit with runtimePM?
> Hi Jeff,
> 
> Can you elaborate?
> 
> In short, with this patch, MHI just wants to give controller the option to
> choose the vote type so we can implement autonomous low power mode entries
> on both host and device.

So, you are attempting to manage the power mode of the device.  The 
standard mechanism to do so in Linux is runtime pm.

https://elixir.bootlin.com/linux/latest/source/Documentation/driver-api/pm/devices.rst

I'm no runtime pm expert, but it feels like your whole voting mechanism, 
etc is just reimplemeting that.  Reimplementing the wheel, when its been 
a standard thing that the majority of the kernel uses is not usually 
acceptable.

IMO, you need some sort of justification why runtime pm is not 
applicable for you, because I'm willing to bet Mani/Greg are going to 
ask the same.

-- 
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.