Messages in this thread | | | Date | Fri, 19 Aug 2011 10:02:00 +0800 | From | Yang Rui Rui <> | Subject | Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and USB_GADGET_SUPERSPEED |
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On 08/19/2011 01:05 AM, Michal Nazarewicz wrote: > 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.
This is what I means in before reply, musb_gadget_start will check the speed set here. if it != USB_SPEED_HIGH it will return -EINVAL.
> > 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 original code, ifndef CONFIG_USB_GADGET_SUPERSPEED and max_speed = USB_SPEED_SUPER then the result will be:
composite_driver.speed = min(USB_SPEED_HIGH, USB_SPEED_SUPER)
For patched code, composite_driver.speed = USB_SPEED_SUPER
> >> 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. >
-- Thanks Yang Ruirui
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