Re: [PATCH] power:power_supply_syfs : Treat PROP_TYPE as a regularattribute first

From: Philippe De Swert
Date: Fri Oct 25 2013 - 19:10:17 EST


On 26/10/13 01:15, Anton Vorontsov wrote:
On Thu, Aug 15, 2013 at 02:09:58AM +0300, Philippe De Swert wrote:
These days we often have USB powered devices. This means that often the
type is variable. Common examples are smartphones which can be charged
through a normal USB port on a PC/laptop, a dedicated charger, etc...
I would guess that a lot of userland code assumes that the type is fixed.
We can't break this assumption. Plus I don't think we really need the
changing types.

That is a fair assumption, but that does not work anymore with smartphones, GPS devices, tablets etc.. Moreover why is it the only property that would be fixed? Also we have the power supply name to identify it, and I expect most userland code uses that.

Userspace sometimes needs to behave differently based on the type of charger
connected to such devices.

A system with several charger should either:

1. Register all of them (mains, usb, etc.) as a separate power supply
device, and then use PROP_ONLINE to specify whether something is connected
to the port or not.
2. Register only the charger type that is currently connected to the

I think I did not make myself very clear. Well there are actually no different chargers here. It is one USB charger input, however its properties are different depending on the actual connected "charger device/type". It is the same charging controller however when a usb cable is connected and power comes from a PC it is very different
from when it is a dedicated USB charger.

Constantly register/unregister the current "charger type" makes it very difficult to monitor. Having a separate power_supply device per possible connected charger type is pretty tedious. We are talking USB_DCP, USB_ACA, USB_CDP, USB already, and new ones probably in the future. Not to mention that at some point we would have to deal with OTG also were we might actually supply power. In any case a lot harder than having a changing type property.

One of the main reasons to monitor this is to have the device react differently depending on what gets plugged in. Pure charging when charger gets connected or mass-storage gadget mode, mtp, ... when a cable is connected. Or eventually switch to a totally different device mode to support things like terminal mode (in cars).

This is how we've been doing things from the very start.

Well a number of upstream charging drivers and non-upstreamed android drivers already change the charger type like for example the isp1704. The patch I proposed just changes the inconsistency with the charger type property as it is the only one that gets treated differently, to
avoid confusion with it.

But I am sure open to better ideas for handling this.



To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at