Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752225AbbLNBgs (ORCPT ); Sun, 13 Dec 2015 20:36:48 -0500 Received: from galahad.ideasonboard.com ([185.26.127.97]:39109 "EHLO galahad.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751996AbbLNBgk (ORCPT ); Sun, 13 Dec 2015 20:36:40 -0500 From: Laurent Pinchart To: Geert Uytterhoeven Cc: Geert Uytterhoeven , Greg Kroah-Hartman , Simon Horman , Magnus Damm , Yoshinori Sato , "linux-serial@vger.kernel.org" , Linux-sh list , "linux-kernel@vger.kernel.org" , Linux PM list Subject: Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() Date: Sun, 13 Dec 2015 21:39:02 +0200 Message-ID: <1466956.fL4LZVx6Ru@avalon> User-Agent: KMail/4.14.8 (Linux/4.1.12-gentoo; KDE/4.14.8; x86_64; ; ) In-Reply-To: References: <1447958344-836-1-git-send-email-geert+renesas@glider.be> <3399561.8ERHTtILhO@avalon> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3409 Lines: 86 Hi Geert, On Thursday 10 December 2015 13:30:18 Geert Uytterhoeven wrote: > On Thu, Nov 19, 2015 at 9:38 PM, Laurent Pinchart wrote: > > On Thursday 19 November 2015 19:38:46 Geert Uytterhoeven wrote: > >> Transfer clock cleanup handling to the core device management code. > >> > >> Signed-off-by: Geert Uytterhoeven > >> --- > >> > >> drivers/tty/serial/sh-sci.c | 8 +++----- > >> 1 file changed, 3 insertions(+), 5 deletions(-) > >> > >> diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c > >> index cba51da604253db6..9442961a198378c7 100644 > >> --- a/drivers/tty/serial/sh-sci.c > >> +++ b/drivers/tty/serial/sh-sci.c > >> @@ -2216,7 +2216,7 @@ static struct uart_ops sci_uart_ops = { > >> > >> static int sci_init_clocks(struct sci_port *sci_port, struct device > >> *dev) > >> { > >> > >> /* Get the SCI functional clock. It's called "fck" on ARM. */ > >> > >> - sci_port->fclk = clk_get(dev, "fck"); > >> + sci_port->fclk = devm_clk_get(dev, "fck"); > > > > Have you tested what happens if you unbind the device from the driver > > while userspace has the serial port open ? > > Yes I have. And I didn't notice any user-visible behavioral differences. > > There is a small ordering difference, though: with clk_get() and clk_put(), > the explicit clk_put() is done before removing the device from its PM > Domain (which involces another call to clk_put() on the module clock): > > device_release_driver > __device_release_driver > platform_drv_remove > sci_remove > sci_cleanup_single > __clk_put > genpd_dev_pm_detach > pm_genpd_remove_device > pm_clk_destroy > __pm_clk_remove > __clk_put > > When using devm_clk_get(), the managed cleanup is done after the device has > been removed from its PM Domain: > > device_release_driver > __device_release_driver > platform_drv_remove > genpd_dev_pm_detach > pm_genpd_remove_device > pm_clk_destroy > __pm_clk_remove > __clk_put > release_nodes > __clk_put > > This shouldn't make a difference, and applies to all other drivers using > devm_*(), and devices that are part of a PM Domain. I was more concerned about the clk_disable_unprepare() calls. The function is called through the uart pm handler which is called when closing the uart (uart_close()). It's a bit difficult to follow the dynamic code paths as I'm not very familiar with the framework, but I was concerned that the would end up calling clk_disable_unprepare() on a clock for which we have no reference anymore. What prevents clk_disable_unprepare() from being called in the close path after the device has been unbound ? And what ensures that the clocks get unprepared when unbinding the device if the port is held open by a userspace process ? -- Regards, Laurent Pinchart -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/