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

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Date:	Thu, 31 Mar 2016 13:06:24 +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

Baolin Wang <baolin.wang@...aro.org> writes:
> [ text/plain ]
> On 31 March 2016 at 16:18, Felipe Balbi <balbi@...nel.org> wrote:
>>
>> 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,
>
> Sorry, I did not get your suggestion, could you give me an example? Thanks.

int default_current_limit = 500;

if (gadget->speed >= USB_SPEED_SUPER)
	default_current_limit = 900;

>>>>>>> +
>>>>>>> +/* 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 ?
>
> I am not sure if userland need the enum usb_charger_state. But I
> remember you want to report the charger state to userland in previous
> email.

right, which means this enumeration definition could be placed in the
UAPI header. Unless, of course, we're reporting strings, rather than
integers, in the sysfs file.

-- 
balbi

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