linux-kernel - Re: [PATCH v1 2/2] usb: gadget: composite: Draw 100mA current if not configured

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Message-ID: <699d0d70-4d83-7bc6-e152-0a352a016e71@quicinc.com>
Date:   Thu, 23 Feb 2023 13:52:22 +0530
From:   Prashanth K <quic_prashk@...cinc.com>
To:     Jack Pham <quic_jackp@...cinc.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Jakob Koschel <jakobkoschel@...il.com>,
        Jó Ágila Bitsch <jgilab@...il.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Pratham Pratap <quic_ppratap@...cinc.com>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] usb: gadget: composite: Draw 100mA current if not
 configured



On 23-02-23 01:03 pm, Jack Pham wrote:
> Hi Prashanth,
> 
> On Thu, Feb 23, 2023 at 10:48:30AM +0530, Prashanth K wrote:
>> Currently we don't change the current value if device isn't in
>> configured state. But the battery charging specification says,
>> the device can draw upto 100mA of current if its in unconfigured
> 
> Here you say spec says "up to" (BTW you have a typo) 100mA...
> 
Will fix it in v2
>> state. Hence add a Vbus_draw work in composite_resume to draw
>> 100mA if the device isn't configured.
> 
> But here and in the patch you are calling the function to draw exactly
> 100mA.  Consider the possibility that a gadget could be configured to
> draw less current than that or not anything at all, we should make sure
> to honor that as an absolute maximum.
That's right
> 
>> Signed-off-by: Prashanth K <quic_prashk@...cinc.com>
>> ---
>>   drivers/usb/gadget/composite.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
>> index fa7dd6c..147d278 100644
>> --- a/drivers/usb/gadget/composite.c
>> +++ b/drivers/usb/gadget/composite.c
>> @@ -2531,6 +2531,8 @@ void composite_resume(struct usb_gadget *gadget)
>>   			usb_gadget_clear_selfpowered(gadget);
>>   
>>   		usb_gadget_vbus_draw(gadget, maxpower);
>> +	} else {
>> +		usb_gadget_vbus_draw(gadget, 100);
> 
> Similar to the configured case, maybe you can perform a min()
> calculation against either or both the config->MaxPower or
> CONFIG_USB_GADGET_VBUS_DRAW.
> 
Thanks for the suggestion, will update it in v2 patch
> Thanks,
> Jack