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

[Baolin Wang <baolin.wang@linaro.org>]

Hi Neil,

On 5 October 2016 at 18:44, NeilBrown <neilb@suse.com> wrote:
> On Wed, Oct 05 2016, Felipe Balbi wrote:
>
>> Hi Baolin,
>>
>> Baolin Wang <baolin.wang@linaro.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.

I transplanted the USB charger framework to our Spreadtrum platform
with implementing the 'get_charger_type' callback to get the charger
type in power driver. Cause we get the charger type from accessing the
PMIC registers not from USB PHY.

>
>>> 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.

Probably not. Now the USB charger framework tried to integrate all
different charger plugged/unplugged events, and all different charger
type getting methods, then noticed the plugged/unplugged events and
charger current to power driver, which I think that is what USB
charger should really do. Moreover, this patchset is reviewed and
helped by many people (thanks Felipe, Greg, Mark, Peter and Jun), I
really hope I can make it better to upstream.

>
> 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.

Not really. Like I said, some platform's charger detection is done by
hardware not USB PHY, thus we can get the charger type from PMIC
hardware registers.

>
>>> 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.

No. User can implement the get_charger_type() method to access the
PMIC registers to get the charger type, which is one very common
method.

>
>>> 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.

So, seems I should report both minimum and maximum.

>
> 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.

USB charger is one virtual device not one actual hardware device, we
should not mess it together with usb_notifier or extcon notifier.

>
> 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.

Usually only one USB charger in one system, I have not seen more than
one charger in a system.

>
> 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.

I think now the current/state/type attributes are enough, which are
USB chargger needed. Thanks.

-- 
Baolin.wang
Best Regards