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SubjectRe: [PATCH v6 0/8] power: add power sequence library
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.

--

Best Regards,
Peter Chen

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