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SubjectRe: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and USB_GADGET_SUPERSPEED
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On Thu, 18 Aug 2011 16:59:28 +0200, Alan Stern <stern@rowland.harvard.edu>  
wrote:

> On Thu, 18 Aug 2011, Michal Nazarewicz wrote:
>
>> On Wed, 17 Aug 2011 23:09:37 +0200, Alan Stern
>> <stern@rowland.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?
>
> Yes, it is.
>
>> 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.
>
> The speed being calculated isn't the speed of the usb_composite_driver;
> it's the speed of the usb_gadget_driver. The gadget itself cannot be
> allowed to run faster than its internal drivers can handle.

Yeah, that's why you set usb_gadget_driver's speed to the speed declared
in usb_composite_driver.

For the most part, usb_composite_probe() is called only once in module's
init function. As far as I know, only g_ffs calls it several times. So
in all cases expect for g_ffs, composite_driver.speed =
min(composite_driver.speed,
driver->max_speed) should have the same effect as composite_driver.speed
= driver->max_speed.

> For example, if you have a composite gadget where one of the function
> drivers can handle SuperSpeed and the other can't go beyond high speed,
> the overall gadget must never run faster than high speed.

Shouldn't that be dealt in usb_add_function()? I cannot see any code that
would do that here atm though.

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


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