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

From: Kishon Vijay Abraham I
Date: Fri Apr 03 2015 - 09:38:53 EST



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>

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>


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

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

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
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?

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