On Mon, Jan 20, 2014 at 11:16:03PM +0000, Russell King - ARM Linux wrote: > On Mon, Jan 20, 2014 at 03:11:41PM -0800, Greg KH wrote: > > On Mon, Jan 20, 2014 at 09:32:06PM +0000, Russell King - ARM Linux wrote: > > > On Mon, Jan 20, 2014 at 01:16:01PM -0800, Greg KH wrote: > > > > On Mon, Jan 20, 2014 at 10:05:30AM +0000, Russell King - ARM Linux wrote: > > > > > On Mon, Jan 20, 2014 at 02:32:34PM +0530, Tushar Behera wrote: > > > > > > uart_register_driver call binds the driver to a specific device > > > > > > node through tty_register_driver call. This should typically happen > > > > > > during device probe call. > > > > > > > > > > > > In a multiplatform scenario, it is possible that multiple serial > > > > > > drivers are part of the kernel. Currently the driver registration fails > > > > > > if multiple serial drivers with same default major/minor numbers are > > > > > > included in the kernel. > > > > > > > > > > > > A typical case is observed with amba-pl011 and samsung-uart drivers. > > > > > > > > > > The samsung-uart driver is at fault here - the major/minor numbers were > > > > > officially registered to amba-pl011. Samsung needs to be fixed properly. > > > > > > > > I agree, the Samsung driver is "broken" here, but that's no reason why > > > > these two drivers can't register with the tty layer _after_ the hardware > > > > is detected, and not before. > > > > > > > > That saves resources on systems that build the drivers in, yet do not > > > > have the hardware present, which is always a good thing. > > > > > > Great, so what you're saying is that we need to wait until the first > > > device calls into the probe function. What about removal... how does > > > a driver know when it's last device has been removed to de-register > > > that? > > > > The "bus" that the device is on handles that, right? > > > > > I guess it needs the driver model to provide some way to know when a > > > driver is completely unbound - but isn't that racy? > > > > How is it racy? That's how the driver model works... > > Think about what happens when the last device unregisters, but a new > device comes along and is probed. > > I don't believe the driver model has any locking to prevent a drivers > ->probe function running concurrently with it's ->remove function for > two (or more) devices. The bus prevents this from happening. > The locking against this is done on a per-device basis, not a per-driver > basis. No, on a per-bus basis. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
