linux-kernel - Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and USB_GADGET

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Date:	Thu, 18 Aug 2011 15:19:20 +0200
From:	"Michal Nazarewicz" <mnazarewicz@...gle.com>
To:	"Alan Stern" <stern@...land.harvard.edu>
Cc:	"Sergei Shtylyov" <sshtylyov@...sta.com>,
	"Felipe Balbi" <balbi@...com>,
	"Sebastian Andrzej Siewior" <bigeasy@...utronix.de>,
	"Yang Rui Rui" <ruirui.r.yang@...to.com>,
	"Greg Kroah-Hartman" <gregkh@...e.de>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and
 USB_GADGET_SUPERSPEED

> On Wed, 17 Aug 2011, Michal Nazarewicz wrote:
>> --- a/drivers/usb/gadget/composite.c
>> +++ b/drivers/usb/gadget/composite.c
>> @@ -1559,12 +1559,6 @@ composite_resume(struct usb_gadget *gadget)
>>  /*-------------------------------------------------------------------------*/
>>
>>  static struct usb_gadget_driver composite_driver = {
>> -#ifdef CONFIG_USB_GADGET_SUPERSPEED
>> -	.speed		= USB_SPEED_SUPER,
>> -#else
>> -	.speed		= USB_SPEED_HIGH,
>> -#endif
>> -
>>  	.unbind		= composite_unbind,
>>
>>  	.setup		= composite_setup,
>> @@ -1609,8 +1603,7 @@ int usb_composite_probe(struct  
>> usb_composite_driver *driver,
>>  		driver->iProduct = driver->name;
>>  	composite_driver.function =  (char *) driver->name;
>>  	composite_driver.driver.name = driver->name;
>> -	composite_driver.speed = min((u8)composite_driver.speed,
>> -				     (u8)driver->max_speed);
>> +	composite_driver.speed = driver->max_speed;
>>  	composite = driver;
>>  	composite_gadget_bind = bind;

On Wed, 17 Aug 2011 23:09:37 +0200, Alan Stern <stern@...land.harvard.edu>  
wrote:
> I see what's going on here.  Your original patch was wrong and then my
> correction was wrong as well.
>
> This line has to remain the way it was (although those (u8) typecasts
> don't seem to be necessary).  Above, you have to initialize
> composite_driver.speed to an appropriate value, probably
> USB_SPEED_SUPER.
>
> What you didn't realize in your original patch is that
> usb_composite_probe() gets called more than once.  Each time it is
> called, it has to adjust composite_driver.speed.

That's sneaky of composite.c...  But is it desired behaviour?  I cannot
came up with a situation where that's what we want.  I would imagine that
usb_composite_probe() should assume the same speed for given
usb_composite_driver regardless if some other slower usb_composite_driver
was loaded.

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michal "mina86" Nazarewicz    (o o)
ooo +-----<email/xmpp: mnazarewicz@...gle.com>-----ooO--(_)--Ooo--
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