Messages in this thread | | | Subject | Re: [PATCHv2] usb: gadget: get rid of USB_GADGET_DUALSPEED and USB_GADGET_SUPERSPEED | Date | Thu, 18 Aug 2011 19:05:20 +0200 | From | "Michal Nazarewicz" <> |
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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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