On Fri, 18 May 2012, Alan Stern wrote: > On Fri, 18 May 2012, Chen Peter-B29397 wrote: > > > Hi Ming, > > > > I have debugged it at this afternoon, your description for this problem > > is correct, the ehci_reset override the ehci->command which is assigned > > at ehci_init, and ehci->command at ehci_init is correct. > > > > My opinion for this fix is just remove the > > " ehci->command = ehci_readl(ehci, &ehci->regs->command);" at ehci_reset. > > Even someone called ehci_reset to reset controller, it can still use command > > value assigned at ehci_init. > > Yes, I see the problem. And you are right; the value assigned during > ehci_init() should not be overridden. > > However... The value assigned in ehci_init() is not fully correct. > That routine does not examine the default value in the USBCMD register > before making its own settings. (It can't -- the USBCMD register may > contain random garbage because the controller hasn't been reset at this > point.) > > This means that ehci_init() can't handle hardware updates. New > versions of the hardware may define bits in USBCMD that the code > doesn't know about. Those bits would be set properly by default when a > hardware reset occurs, but then ehci_init() would wipe them out. > > It looks like a bunch of code needs to be moved from ehci_init() to > ehci_reset() -- everything involved in computing ehci->command. The > idea is that once the controller has been reset, we first set > ehci->command to the value in the USBCMD register (as is done now). > Then we can modify the bits we know about (as the code in ehci_init() > does) while leaving the other bits alone. A simpler idea just occurred to me. All we need to do is change the line in ehci_reset() that assigns ehci->command. What it should do is mask out the bits that were set up in ehci_init(). Those bits should be kept unchanged in ehci->command. The remaining bits should be set according to the value read from the USBCMD register. Would anyone like to code that up? Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
