From mboxrd@z Thu Jan 1 00:00:00 1970 From: skannan@codeaurora.org (Saravana Kannan) Date: Thu, 27 Jan 2011 12:30:36 -0800 Subject: Locking in the clk API In-Reply-To: <20110127085438.GA25239@n2100.arm.linux.org.uk> References: <201101111016.42819.jeremy.kerr@canonical.com> <20110111091607.GI12552@n2100.arm.linux.org.uk> <201101111744.59712.jeremy.kerr@canonical.com> <20110111103929.GN24920@pengutronix.de> <4D386ABF.9060908@fluff.org> <20110120190822.GK6335@n2100.arm.linux.org.uk> <4D3932B4.8010904@codeaurora.org> <20110121094042.GD13235@n2100.arm.linux.org.uk> <4D40F5CC.6080809@codeaurora.org> <20110127085438.GA25239@n2100.arm.linux.org.uk> Message-ID: <4D41D5EC.6030405@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 01/27/2011 12:54 AM, Russell King - ARM Linux wrote: > On Wed, Jan 26, 2011 at 08:34:20PM -0800, Saravana Kannan wrote: >> I'm not too familiar with serial/tty, does anyone know if the >> .set_termios needs to be atmoic? If not, we could just change >> cpm_uart/cpm_uart_core.c to use mutex instead of spinlock. > > The locking is there to protect against the interrupt handler accessing > the port->* stuff (which seems to have been forgotten by the cpm driver). > > I don't see any reason why clk_set_rate() needs to be under the spinlock > there - we need the reprogramming of the baud rate within the spinlock > on 8250 because of DLAB bit hiding the data registers. It's also a good > idea that it _is_ within the spinlock along with uart_update_timeout() > to ensure timeouts and the baud rate are updated together. For internal tree purposes, does .set_termios need to be atomic? Can it grab mutexes instead of spinlock? Going back to the topic, how about CPU freq drivers possibly using clk_set_rate() to change freq? Do you think that's not the case or a concern? All, Do any one of your mach's control CPU freq using clk_set_rate() and does it need to be atomic? CPUfreq doesn't need it to be atomic. So, you will need clk_set_rate() to be atomic only if you try to use it to lower CPU freq very late during idle/suspend. -Saravana -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.