Subject: RE: [PATCH] extcon : callback function to read cable property
From: anish kumar <anish198519851985@gmail.com>
To: "Tc, Jenny" <jenny.tc@intel.com>
Cc: Chanwoo Choi <cw00.choi@samsung.com>,
        "myungjoo.ham@samsung.com" <myungjoo.ham@samsung.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "myunjoo.ham@gmail.com" <myunjoo.ham@gmail.com>, lockwood@android.com,
        peterhuewe@gmx.de, broonie@opensource.wolfsonmicro.com,
        gregkh@linuxfoundation.org, lars@metafoo.de, jic23@kernel.org
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Date: Sat, 10 Nov 2012 13:18:02 +0900
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On Fri, 2012-11-09 at 14:05 +0000, Tc, Jenny wrote:
> > I think that the role of extcon subsystem notify changed
> > state(attached/detached) of cable to notifiee, but if you want to add
> > property feature of cable, you should solve ambiguous issues.
> > 
> > First,
> > This patch only support the properties of charger cable but, never support
> > property of other cable. The following structure depend on only charger
> > cable. We can check it the following structure:
> > 	struct extcon_chrg_cbl_props {
> > 		enum extcon_chrgr_cbl_stat cable_state;
> > 		unsigned long mA;
> > 	};
> > 
> > I think that the patch have to support all of cables for property feature.
> 
> My suggestion is to have a structure like this 
> 
> struct  extcon_cablel_props {
> 	unsigned int cable_state;
>     	unsigned int data; 
Why can't it be float/long/double??
> }
> Not all cables will have more than two states. If any cable has more than two states,
> the above structure makes it flexible to represent additional state and the data associated
> 
> > 
> > Second,
> > Certainly, you should define common properties of all cables and specific
> > properties of each cable. The properties of charger cable should never be
> > defined only.
IMHO the extcon doesn't know anything about the cable except the state
which is currently it is in and which also is set by the provider.I am
unable to understand why should extcon provide more than what it
knows?It should just limit itself to broadcasting the cable state and
exploiting it for any other information would only lead to more
un-necessary code.
It should be same as IIO subsystem where the consumer and provider knows
before hand what information they are going to share and with what
precision and IIO core is just a way to do that.It doesn't know anything
beyond what is given by the provider.
Same is the case with driver core where individual driver sets it's own
private data and the driver core just gives that private data back to
the driver as and when it needs but parsing the private data in the
right way is up to the individual driver.

I fail to understand why is not the case here. 
> 
> Hope above structure would be enough to represent the common cable state and
> it's data. If a cable has more than two states, then extcon_update_state can be used to
> notify the consumer
> 1)Provider can just toggle the "state" argument to notify the consumer that cable state is 
> changed
> OR
> 2) Add one more argument  like  extcon_update_state(struct extcon_dev *edev, u32 mask, u32 state1, u32 sate2)
This will cause other drivers to change such as arizona.
> If the state2 is set, then consumers can use get_cable_properties() to query the cable properties. State2 need to be
> used only if the cable need to represent more than two state
> 
> > 
> > Third,
> > If we finish to decide the properties for all cables, I'd like to see a example
Why do we think that state and property is the only thing which the
consumer want to know?I am sure there would be some more properties
which would be of some interest to consumers and there is quite a
possibility that in future we might get a patch for that also.So instead
of that limiting it to just state is a good idea.
> > code.
> 
> Agreed. If we  agree on the above structure, I can modify the charging subsystem patch
> to use the same structure. (https://lkml.org/lkml/2012/10/18/219). This would give a reference
> for the new feature.
> 
> > 
> > You explained following changed state of USB according to Host state on
> > other patch.
> > ---------------------------
> > For USB2.0
> > 1) CONNECT (100mA)->UPDATE(500mA)->DISCONNECT(0mA)
> > 2) CONNECT (100mA)->UPDATE(500mA)->HOST SUSPEND(2.5mA/500mA)-
> > >DISCONNECT(0mA)
> > 3) CONNECT (100mA)->UPDATE(500mA)->HOST SUSPEND(2.5mA/500mA)-
> > >HOST RESUME(500mA)->DISCONNECT(0mA)
> > 
> > For USB 3.0
> > 4) CONNECT (150mA)->UPDATE(900mA)->DISCONNECT(0mA)
> > 5) CONNECT (150mA)->UPDATE(900mA)-> HOST SUSPEND(2.5mA/900mA)-
> > >DISCONNECT(0mA)
> > 6) CONNECT (100mA)->UPDATE(900mA)->HOST SUSPEND(2.5mA/900mA)-
> > >HOST RESUME(900mA)->DISCONNECT(0mA)
> > ---------------------------
> > 
> > I have a question. Can the provider device driver(e.g., extcon-max77693.c/
> > extcon-max8997.c) detect the changed state of host? I'd like to see the
> > example device driver that the provider device driver detect changed state
> > of host.
> > Could you provide example device driver?
> 
> Good question. The OTG drivers are capable of identifying the SUSPEND event.
> System cannot setup SDP (USB host) charging with maximum charging current - 500mA
> (USB2.0/ 900mA(USB 3)) without enumerating the USB. The USB enumeration can be
> done only with a USB/OTG driver. IMHO the above extcon drivers
> (extcon-max77693.c/ extcon-max8997.c) are not capable of doing the USB enumeration
> and identifying the charge current. They can just identify the charger type - 
> SDP/DCP/CDP/ACA/AC. The intelligence for USB enumeration 
> should be inside USB/OTG driver.
> 


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