Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932323AbbLNKeQ (ORCPT ); Mon, 14 Dec 2015 05:34:16 -0500 Received: from mail-ob0-f169.google.com ([209.85.214.169]:36106 "EHLO mail-ob0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932193AbbLNKeM (ORCPT ); Mon, 14 Dec 2015 05:34:12 -0500 MIME-Version: 1.0 In-Reply-To: <1466956.fL4LZVx6Ru@avalon> References: <1447958344-836-1-git-send-email-geert+renesas@glider.be> <3399561.8ERHTtILhO@avalon> <1466956.fL4LZVx6Ru@avalon> Date: Mon, 14 Dec 2015 11:34:11 +0100 X-Google-Sender-Auth: 5Yfj3HXruJmSIZ7TucDPRZR3pVg Message-ID: Subject: Re: [PATCH 07/25] serial: sh-sci: Convert from clk_get() to devm_clk_get() From: Geert Uytterhoeven To: Laurent Pinchart 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 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4143 Lines: 98 Hi Laurent, On Sun, Dec 13, 2015 at 8:39 PM, Laurent Pinchart wrote: > 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 ? Both questions are answered by uart_hangup(): - uart_hangup() sets port->count to zero, hence uart_close() returns early (second return statement), long before it would call the uart pm handler. - uart_hangup() calls uart_change_pm(state, UART_PM_STATE_OFF); Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds -- 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/