On Thu, 18 Aug 2011 16:59:28 +0200, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
wrote:
On Thu, 18 Aug 2011, Michal Nazarewicz wrote:
On Wed, 17 Aug 2011 23:09:37 +0200, Alan Stern
<stern@xxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxx>-----ooO--(_)--Ooo--
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