linux-kernel - Re: [PATCH v7 1/4] gadget: Introduce the usb charger framework

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Date:	Thu, 31 Mar 2016 11:18:06 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Baolin Wang <baolin.wang@...aro.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Sebastian Reichel <sre@...nel.org>,
	Dmitry Eremin-Solenikov <dbaryshkov@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Peter Chen <peter.chen@...escale.com>,
	Alan Stern <stern@...land.harvard.edu>, r.baldyga@...sung.com,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Lee Jones <lee.jones@...aro.org>,
	Mark Brown <broonie@...nel.org>,
	Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>,
	patches@...nsource.wolfsonmicro.com,
	Linux PM list <linux-pm@...r.kernel.org>,
	USB <linux-usb@...r.kernel.org>,
	device-mainlining@...ts.linuxfoundation.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 1/4] gadget: Introduce the usb charger framework


Hi,

Baolin Wang <baolin.wang@...aro.org> writes:
>>>>> +#define DEFAULT_SDP_CUR_LIMIT        (500 - DEFAULT_CUR_PROTECT)
>>>>
>>>> According to the spec we should always be talking about unit loads (1
>>>> unit load is 100mA for HS/FS/LS and 150mA for SS). Also, this will not
>>>> work for SS capable ports and SS gadgets (we have quite a few of them,
>>>> actually). You're missing the opportunity of charging at 900mA.
>>>
>>> I follow the DCP/SDP/CDP/ACA type's default current limitation and
>>> user can set them what they want.
>>
>> no, the user CANNOT set it to what they want. If you get enumerated
>> @100mA and the user just decides to set it to 2000mA, s/he could even
>> melt the USB connector. The kernel _must_ prevent such cases.
>>
>> In any case, DEFAULT_SDP_CUR_LIMIT shouldn't be a constant, it should be
>> variable because if you enumerate in SS, you _can_ get up to 900mA.
>
> Make sense. But these are just default values. They can be changed
> safely by power driver with 'usb_charger_set_cur_limit_by_type()'
> function to set 900mA.

oh okay. Still, the default value should be a function of gadget->speed,
IMO ;-)

>>>>> +
>>>>> +/* USB charger state */
>>>>> +enum usb_charger_state {
>>>>> +     USB_CHARGER_DEFAULT,
>>>>> +     USB_CHARGER_PRESENT,
>>>>> +     USB_CHARGER_REMOVE,
>>>>> +};
>>>>
>>>> userland really doesn't need these two ?
>>>
>>> We've reported to userspace by kobject_uevent in
>>> 'usb_charger_notify_others()' function.
>>
>> I mean as a type ;-) So userspace doesn't have to redefine these for
>> their applications.
>
> Make sense. I can introduce some sysfs files for userspace. Thanks for
> your comments.

okay, my reply was a bit cryptic, but what I mean here is that enum
usb_charger_state could be moved your include/uapi header. My question
is, then, does userland need to have knowledge of enum
usb_charger_state ?

-- 
balbi

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