Re: [PATCH 0/5] Enhancements to twl4030 phy to support better charging - V2

[Kishon Vijay Abraham I]

+Extcon MAINTAINERS

Hi,

On Wednesday 01 April 2015 10:11 AM, NeilBrown wrote:
> On Thu, 26 Mar 2015 05:29:42 +0530 Kishon Vijay Abraham I <kishon@xxxxxx>
> wrote:
>
> > Hi NeilBrown,
> >
> > On Thursday 26 March 2015 02:52 AM, NeilBrown wrote:
> > > On Thu, 26 Mar 2015 02:46:32 +0530 Kishon Vijay Abraham I <kishon@xxxxxx>
> > > wrote:
> > >
> > > > Hi,
> > > >
> > > > On Monday 23 March 2015 04:05 AM, NeilBrown wrote:
> > > > > Hi Kishon,
> > > > >   I wonder if you could queue the following for the next merge window.
> > > > >   They allow the twl4030 phy to provide more information to the
> > > > >   twl4030 battery charger.
> > > > >   There are only minimal changes since the first version, particularly
> > > > >   documentation has been improved.
> > > >
> > > > There are quite a few things in this series which use the USB PHY library
> > > > interface which is kindof deprecated. We should try and use the Generic PHY
> > > > library for all of them. It would also be better to add features to the
> > > > PHY framework if the we can't achieve something with the existing PHY
> > > > framework.
> > >
> > > Hi,
> > >   are you able to more specific at all?  What is the "USB PHY library"?
> > > Where exactly is the "PHY framework"?
> >
> > There is a USB PHY library that exists in drivers/usb/phy/phy.c and there is
> > a Generic PHY framework that is present in drivers/phy/phy-core.c. twl4030
> > actually supports both the framework.
> >
> > In your patch whatever uses struct usb_phy uses the old USB PHY library and
> > whatever uses struct phy uses the generic PHY framework. (Actually your patch
> > does not use the PHY framework at all). We want to deprecate using the USB PHY
> > library and make everyone use the generic PHY framework. Adding features
> > to a driver using the USB PHY library will make the transition to generic PHY
> > framework a bit more difficult.
> >
> > Now all the features that is supported in the USB PHY library may not be
> > supported by the PHY framework. So we should start extending the PHY framework
> > instead of using the USB PHY library.
> >
> > One think I noticed in your driver is using atomic notifier chain. IMO extcon
> > framework should be used in twl4030 USB driver to notify the controller driver
> > instead of using USB PHY notifier. For all other things we have to see if it
> > can be added in the PHY framework.
>
> I've had a look at the code with these issues in mind, and there is one issue
> that I'm not sure about.
>
> In phy-twl4030-usb, the usb_phy is used to hold a reference to the
> 'struct otg', and for passing cable state changes to the notifier.

right now we directly call omap_musb_mailbox no? we don't use notifiers right?
> The former probably has to stay until musb can keep a reference to the otg,
> separate form the usb_phy.  The latter can be changed to use extcon - to
> some extent.  I actually have patches to do that from a couple of years back,
> but I never proceeded with them.
>
> The problem is that one thing that needs to be communicated to the charger is
> the max current that was negotiated by a "Standard Downstream Port".
> This could be 500mA from a powered hum, or much less from an unpowered hub.
> (Currently the usb gadget code does negotiated between different
> possibilities, but it could and hopefully will one day).
>
> With the notifier chain there is an easy way to communicate the allowed
> current once it is negotiated. e.g. ab8500_usb_set_power() does this.
>
> 'struct phy' has no equivalent of the 'set_power' callback  which 'struct
> usb_phy' provides, and extcon has no mechanism (that I can see) for
> communicating a number - just binary cable states.

Chanwoo Choi, Can this be modified so that we can communicate numbers like in
the case of EXTCON_CHARGE_DOWNSTREAM?
> Presumably a 'set_power' method could be added to 'struct phy' so the
> usb-core can communicate the number to the phy, but it is not clear to me how
> the 'phy' can communicate it to the charger.

Should the PHY be involved in all this? We can make the gadget driver
directly communicate the value to the charger no?
> The 'phy' could provide an API to request the current negotiated max current,
> but there still needs to be a way to let the charger know that this has
> changed.
> That could in theory be done via extcon, by having a secondary
> 'USB_connected' cable type, but it isn't really a cable type and pretending
> that it is seems wrong.

I think EXTCON_CHARGE_DOWNSTREAM was created for that purpose. Chanwoo?

Thanks
Kishon
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