Message-ID: <fd94340b-1c1d-2307-7e57-5b05f1655d2c@linaro.org>
Date:   Wed, 31 Aug 2016 22:28:20 +0530
From:   Vaibhav Hiremath <vaibhav.hiremath@...aro.org>
To:     Peter Chen <hzpeterchen@...il.com>
Cc:     robh+dt@...nel.org, Peter Chen <peter.chen@....com>,
        gregkh@...uxfoundation.org, stern@...land.harvard.edu,
        ulf.hansson@...aro.org, broonie@...nel.org, sre@...nel.org,
        shawnguo@...nel.org, dbaryshkov@...il.com, dwmw3@...radead.org,
        mark.rutland@....com, devicetree@...r.kernel.org,
        k.kozlowski@...sung.com, linux-usb@...r.kernel.org,
        oscar@...andei.net, pawel.moll@....com, arnd@...db.de,
        linux-pm@...r.kernel.org, festevam@...il.com,
        s.hauer@...gutronix.de, stephen.boyd@...aro.org,
        linux-kernel@...r.kernel.org, troy.kisky@...ndarydevices.com,
        stillcompiling@...il.com, p.zabel@...gutronix.de,
        mail@...iej.szmigiero.name, mka@...omium.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 0/8] power: add power sequence library



On Wednesday 31 August 2016 03:22 PM, Peter Chen wrote:
> On Wed, Aug 31, 2016 at 01:46:30PM +0530, Vaibhav Hiremath wrote:
>>
>> On Monday 29 August 2016 04:40 PM, Peter Chen wrote:
>>> On Wed, Aug 24, 2016 at 04:53:35PM +0800, Peter Chen wrote:
>>>> On Tue, Aug 23, 2016 at 04:02:48PM +0530, Vaibhav Hiremath wrote:
>>>>> On Monday 15 August 2016 02:43 PM, Peter Chen wrote:
>>>>>> Hi all,
>>>>>>
>>>>>> This is a follow-up for my last power sequence framework patch set [1].
>>>>>> According to Rob Herring and Ulf Hansson's comments[2], I use a generic
>>>>>> power sequence library for parsing the power sequence elements on DT,
>>>>>> and implement generic power sequence on library. The host driver
>>>>>> can allocate power sequence instance, and calls pwrseq APIs accordingly.
>>>>>>
>>>>>> In future, if there are special power sequence requirements, the special
>>>>>> power sequence library can be created.
>>>>>>
>>>>>> This patch set is tested on i.mx6 sabresx evk using a dts change, I use
>>>>>> two hot-plug devices to simulate this use case, the related binding
>>>>>> change is updated at patch [1/6], The udoo board changes were tested
>>>>>> using my last power sequence patch set.[3]
>>>>>>
>>>>>> Except for hard-wired MMC and USB devices, I find the USB ULPI PHY also
>>>>>> need to power on itself before it can be found by ULPI bus.
>>>>>>
>>>>>> [1]http://www.spinics.net/lists/linux-usb/msg142755.html
>>>>>> [2]http://www.spinics.net/lists/linux-usb/msg143106.html
>>>>>> [3]http://www.spinics.net/lists/linux-usb/msg142815.html
>>>>> (Please ignore my response on V2)
>>>>>
>>>>> Sorry being so late in the discussion...
>>>>>
>>>>> If I am not missing anything, then I am afraid to say that the
>>>>> generic library
>>>>> implementation in this patch series is not going to solve many of
>>>>> the custom
>>>>> requirement of power on, off, etc...
>>>>> I know you mentioned about adding another library when we come
>>>>> across such platforms, but should we not keep provision (or easy
>>>>> hooks/path)
>>>>> to enable that ?
>>>>>
>>>>> Let me bring in the use case I am dealing with,
>>>>>
>>>>>
>>>>>                                Host
>>>>>                                 |
>>>>>                                 V
>>>>>                             USB port
>>>>> ------------------------------------------------------------
>>>>>                                 |
>>>>>                                 V
>>>>>                        USB HUB device (May need custom on/off seq)
>>>>>                                 |
>>>>>                                 V
>>>>>                =============================
>>>>>               |                             |
>>>>>               V                             V
>>>>>           Device-1                       Device-2
>>>>> (Needs special power               (Needs special power
>>>>>   on/off sequence.                   on/off sequence.
>>>>>   Also may need custom               Also, may need custom
>>>>>   sequence for                       sequence for
>>>>>   suspend/resume)                    suspend/resume)
>>>>>
>>>>>
>>>>> Note: Both Devices are connected to HUB via HSIC and may differ
>>>>>            in terms of functionality, features they support.
>>>>>
>>>>> In the above case, both Device-1 and Device-2, need separate
>>>>> power on/off sequence. So generic library currently we have in this
>>>>> patch series is not going to satisfy the need here.
>>>>>
>>>>> I looked at all 6 revisions of this patch-series, went through the
>>>>> review comments, and looked at MMC power sequence code;
>>>>> what I can say here is, we need something similar to
>>>>> MMC power sequence here, where every device can have its own
>>>>> power sequence (if needed).
>>>>>
>>>>> I know Rob is not in favor of creating platform device for
>>>>> this, and I understand his comment.
>>>>> If not platform device, but atleast we need mechanism to
>>>>> connect each device back to its of_node and its respective
>>>>> driver/library fns. For example, the Devices may support different
>>>>> boot modes, and platform driver needs to make sure that
>>>>> the right sequence is followed for booting.
>>>>>
>>>>> Peter, My apologies for taking you back again on this series.
>>>>> I am OK, if you wish to address this in incremental addition,
>>>>> but my point is, we know that the current generic way is not
>>>>> enough for us, so I think we should try to fix it in initial phase only.
>>>>>
>>>> Rob, it seems generic power sequence can't cover all cases.
>>>> Without information from DT, we can't know which power sequence
>>>> for which device.
>>>>
>>> Vaibhav, do you agree that I create pwrseq library list using postcore_initcall
>>> for each library, and choose pwrseq library according to compatible
>>> string first, if there is no compatible string for this library, just
>>> use generic pwrseq library.
>>>
>> Lets hear from MMC folks. Ulf, do you agree on approach
>> for pwr seq ??
>>
>>
>> With above approach, I kind of agree on it, but I have couple
>> of comments,
>>
>>   - How DTS looks like now ?? Can you put example here ?
> The dts is the same with current version.

How would consumer driver get the power sequence ?
You must point to right power sequence driver.
For example, in the above example, Device-1, should
get handle to pwrseq-1, and Device-2 to pwrseq-2.

>>   - Should we merge MMC power sequence in next series ?
>>     We also can take this as an incremental change, to avoid further
>>     delay :)
> We had an agreement that keep mmc's pwrseq framework unchanging.
> Unless Ulf and rob both agree to change.

Why 2 separate approach for same problem ?
And I see this as possible duplication of code/functionality :)

Rob ??? Ulf ???

>>   - Lets also add suspend/resume callback to struct pwrseq
>>
> Why suspend/resume can't do at related driver's suspend/resume API?

Nope...
The pwrseq library would have taken ownership of resources, so
related driver cannot suspend the device. Again it is architecture
specific, but we should have provision to handle this.

The system I am dealing with today, does need suspend/resume
callback. To be precise, suspend is close to off state for some devices or
they could enter standby or different low power state, but to do that,
we need same resource as used for ON/OFF functionality.


Thanks,
Vaibhav
>> There are some comments I have on the patches,
>> I will respond directly on respective patches, it would be useful
>> for next series.
>>
> Thanks.
>

-- 
Thanks,
Vaibhav

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