Date:   Mon, 29 Aug 2016 19:10:45 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Vaibhav Hiremath <vaibhav.hiremath@...aro.org>, robh+dt@...nel.org
Cc:     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 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.

-- 

Best Regards,
Peter Chen

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