Message-ID: <eb032ff2-dac4-5efe-dda0-96404f290aa8@linaro.org>
Date:   Tue, 6 Sep 2016 15:48:34 +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

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On Friday 02 September 2016 06:40 AM, Peter Chen wrote:
> On Wed, Aug 31, 2016 at 10:28:20PM +0530, Vaibhav Hiremath wrote:
>>
>> 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:
>>>>>>> veOn 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.
> According to compatible string at device's of_node, we will have a list
> for power sequence libraries which has index (or name), and matches
> compatible string.
>
>>>>   - 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 :)
> How the new kernel compatibles old dts? If we do not need to
> consider this problem, the mmc can try to use power sequence library
> too in future.

I think we should attempt to get both MMC and USB power seq
come on one agreement, so that it can be reused.

MMC Power Seq :
  It is based on platform_device/platform_driver approach,

USB Power seq :
  We are trying to propose library approach, with compatible string match.

We should try to have one approach.
>
>>>>   - 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.
>>
> Ok, I will have API for suspend/resume. You can implement it at your own
> library or generic one.
>

Yeup. Sure.

-- 
Thanks,
Vaibhav

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