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

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Date:	Thu, 31 Mar 2016 19:12:32 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Felipe Balbi <balbi@...nel.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

On 31 March 2016 at 18:06, Felipe Balbi <balbi@...nel.org> wrote:
> 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;

Make sense.

>
>>>>>>>> +
>>>>>>>> +/* 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.

OK. Thanks.

>
> --
> balbi



-- 
Baolin.wang
Best Regards