From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [PATCH 1/2] serial: samsung: Move uart_register_driver call to device probe Date: Mon, 20 Jan 2014 15:11:41 -0800 Message-ID: <20140120231141.GA2355@kroah.com> References: <1390208555-27770-1-git-send-email-tushar.behera@linaro.org> <1390208555-27770-2-git-send-email-tushar.behera@linaro.org> <20140120100530.GY15937@n2100.arm.linux.org.uk> <20140120211601.GB634@kroah.com> <20140120213206.GJ15937@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140120213206.GJ15937@n2100.arm.linux.org.uk> Sender: linux-serial-owner@vger.kernel.org To: Russell King - ARM Linux Cc: Tushar Behera , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-samsung-soc@vger.kernel.org, jslaby@suse.cz, ben.dooks@codethink.co.uk, broonie@kernel.org List-Id: linux-samsung-soc@vger.kernel.org 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... thanks, greg k-h