Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753202AbbLNPr7 (ORCPT ); Mon, 14 Dec 2015 10:47:59 -0500 Received: from galahad.ideasonboard.com ([185.26.127.97]:40139 "EHLO galahad.ideasonboard.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753075AbbLNPrO (ORCPT ); Mon, 14 Dec 2015 10:47:14 -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: Mon, 14 Dec 2015 17:47:26 +0200 Message-ID: <6019540.MWUM70YBzM@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> <1466956.fL4LZVx6Ru@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: 4048 Lines: 93 Hi Geert, On Monday 14 December 2015 11:34:11 Geert Uytterhoeven wrote: > 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); Thank you for making me slightly wiser :-) -- 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/