linux-kernel - Re: [PATCH 3/5] usb: gadget: gmidi: remove bus powered requirement on bmAttributes

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Message-ID: <270D9ECD-1810-48BC-BBE9-9C9DD5E44D4F@felipetonello.com>
Date:	Fri, 04 Mar 2016 18:46:18 +0000
From:	Felipe Ferreri Tonello <eu@...ipetonello.com>
To:	Felipe Balbi <balbi@...nel.org>, linux-usb@...r.kernel.org
CC:	linux-kernel@...r.kernel.org,
	Michal Nazarewicz <mina86@...a86.com>,
	Clemens Ladisch <clemens@...isch.de>
Subject: Re: [PATCH 3/5] usb: gadget: gmidi: remove bus powered requirement on bmAttributes

Hi Balbi, 

On March 4, 2016 7:16:42 AM GMT+00:00, Felipe Balbi <balbi@...nel.org> wrote:
>
>Hi,
>
>"Felipe F. Tonello" <eu@...ipetonello.com> writes:
>> [ text/plain ]
>> This gadget uses a bmAttributes and MaxPower that requires the USB
>bus to be
>> powered from the host, which is not correct because this
>configuration is device
>> specific, not a USB-MIDI requirement.
>>
>> This patch adds two modules parameters, bmAttributes and MaxPower,
>that allows
>> the user to set those flags. The default values are what the gadget
>used to use
>> for backward compatibility.
>>
>> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
>> ---
>>  drivers/usb/gadget/legacy/gmidi.c | 14 ++++++++++++--
>>  1 file changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/legacy/gmidi.c
>b/drivers/usb/gadget/legacy/gmidi.c
>> index fc2ac150f5ff..0553435cc360 100644
>> --- a/drivers/usb/gadget/legacy/gmidi.c
>> +++ b/drivers/usb/gadget/legacy/gmidi.c
>> @@ -63,6 +63,14 @@ static unsigned int out_ports = 1;
>>  module_param(out_ports, uint, S_IRUGO);
>>  MODULE_PARM_DESC(out_ports, "Number of MIDI output ports");
>>  
>> +static unsigned int bmAttributes = USB_CONFIG_ATT_ONE;
>> +module_param(bmAttributes, uint, S_IRUGO);
>> +MODULE_PARM_DESC(bmAttributes, "Configuration Descriptor's
>bmAttributes parameter");
>> +
>> +static unsigned int MaxPower = CONFIG_USB_GADGET_VBUS_DRAW;
>> +module_param(MaxPower, uint, S_IRUGO);
>> +MODULE_PARM_DESC(MaxPower, "Used to calculate Configuration
>Descriptor's bMaxPower parameter");
>
>you didn't run checkpatch, did you ? Also, are you sure you will need
>to
>change this by simply reloading the module ? I'm not convinced.

Yes I always run checkpatch :) 

What do you mean by reloading the module? 

>
>> @@ -119,8 +127,8 @@ static struct usb_configuration midi_config = {
>>  	.label		= "MIDI Gadget",
>>  	.bConfigurationValue = 1,
>>  	/* .iConfiguration = DYNAMIC */
>> -	.bmAttributes	= USB_CONFIG_ATT_ONE,
>
>nack, nackety nack nack nack :-)
>
>USB_CONFIG_ATT_ONE *must* always be set. With your module parameter you
>give users the oportunity to violate USB spec.

You are right. It needs to check the value before it assigns to bmAttributes. 

Felipe 

-- 
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