linux-kernel - Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

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Date:   Wed, 05 Oct 2016 21:44:39 +1100
From:   NeilBrown <neilb@...e.com>
To:     Felipe Balbi <balbi@...nel.org>,
        Baolin Wang <baolin.wang@...aro.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Sebastian Reichel <sre@...nel.org>,
        Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
        David Woodhouse <dwmw2@...radead.org>, robh@...nel.org,
        Jun Li <jun.li@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Ruslan Bilovol <ruslan.bilovol@...il.com>,
        Peter Chen <peter.chen@...escale.com>,
        Alan Stern <stern@...land.harvard.edu>, r.baldyga@...sung.com,
        grygorii.strashko@...com,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Lee Jones <lee.jones@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
        patches@...nsource.wolfsonmicro.com,
        Linux PM list <linux-pm@...r.kernel.org>,
        USB <linux-usb@...r.kernel.org>,
        device-mainlining@...ts.linuxfoundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        "Bird\, Timothy" <Tim.Bird@...sony.com>
Subject: Re: [PATCH v16 0/4] Introduce usb charger framework to deal with the usb gadget power negotation

On Wed, Oct 05 2016, Felipe Balbi wrote:

> Hi Baolin,
>
> Baolin Wang <baolin.wang@...aro.org> writes:
>>>> But you do!
>>>> The mA number from the USB configuration is passed to usb_gadget_vbus_draw.
>>>> Your patch passes that to usb_charger_set_cur_limit_by_type()
>>>> which calls __usb_charger_set_cur_limit_by_type() which will set the
>>>> cur_limit for whichever type uchger->type currently is.
>>>>
>>>> So when it is not relevant, your code *does* set some current limit.
>>>
>>> Suppose the charger type is DCP(it is not relevant to the mA number
>>> from the USB configuration ), it will not do the USB enumeration, then
>>> no USB configuration from host to set current.
>>
>> From the talking, there are some issues (thanks for Neil's comments)
>> need to be fixed as below:
>> 1. Need to add the method getting charger type from extcon subsystem.
>> 2. Need to remove the method getting charger type from power supply.
>> 3. There are still some different views about reporting the maximum
>> current or minimum current to power driver.
>>
>> Now the current v16 patchset can work well on my Spreadtrum platform
>> and Jun's NXP platform, if you like to apply this patchset then I can

I'm really curious how much testing this has had.  Have you actually
plugged in different cable types (SDP DCP DCP ACA) and has each one been
detected correctly?  Because I cannot see how that could happen with the
code you have posted.

>> send out new patches to fix above issues. If you don't like that, I
>> can send out new version patchset to fix above issues. Could you  give
>> me some suggestions what should I do next step? Thanks.
>
> Merge window just opened, nothing will happen for about 2 weeks. How
> about you send a new version after merge window closes and we go from
> there? Fixing 1 and 2 is needed. 3 we need to consider more
> carefully. Perhaps report both minimum and maximum somehow?
>
> Neil, comments?

This probably seems a bit harsh, but I really think the current patchset
should be discarded and the the project started again with a clear
vision of what is required.  What we currently have is too confused.

To respond to the points:
>> 1. Need to add the method getting charger type from extcon subsystem.

Yes.  This should be the only way to get the charger type.

>> 2. Need to remove the method getting charger type from power supply.

Also need to remove the ->get_charger_type() method as there is no
credible use-case for this.

>> 3. There are still some different views about reporting the maximum
>> current or minimum current to power driver.

I think those were resolved.  There was some confusion over whether a
particular power manager wanted to be told the maximum or the minimum,
but I think both have a clear use case in different hardware.

Also: We don't want another notifier_chain.  The usb_notifier combined
with the extcon notifier are sufficient.  Possibly it would be sensible
to replace the usb notifier with a new new notifier chain, but don't add
something without first cleaning up what is there.

Also: resolve the question of whether it could ever make sense to have
 more than one "usb_charger" in a system.  If it doesn't, make it an
 obvious singleton.  If it does, make it clear how the correct
 usb_charger is chosen.

Also: think very carefully before exposing any details through sysfs.
  Some of the details are already visible, either in sys/class/extcon
  or sys/class/power_supply.  Don't duplicate without good reason.

NeilBrown

>
> -- 
> balbi

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