Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752514AbcDZJYx (ORCPT ); Tue, 26 Apr 2016 05:24:53 -0400 Received: from mail.kernel.org ([198.145.29.136]:49089 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752055AbcDZJYt (ORCPT ); Tue, 26 Apr 2016 05:24:49 -0400 Date: Tue, 26 Apr 2016 17:24:15 +0800 From: Shawn Guo To: Dong Aisheng Cc: Stefan Agner , "kernel@pengutronix.de" , Michael Turquette , Stephen Boyd , "linux-arm-kernel@lists.infradead.org" , linux-clk@vger.kernel.org, "linux-kernel@vger.kernel.org" , mingo@redhat.com, tglx@linutronix.de Subject: Re: [PATCH 1/2] clk: imx: do not sleep if IRQ's are still disabled Message-ID: <20160426092414.GH8870@tiger> References: <1454107764-19876-1-git-send-email-stefan@agner.ch> <20160421034520.GA19965@shlinux2.ap.freescale.net> <20160426012341.GB8870@tiger> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2914 Lines: 74 On Tue, Apr 26, 2016 at 01:51:13PM +0800, Dong Aisheng wrote: > Hi Shawn, > > On Tue, Apr 26, 2016 at 9:23 AM, Shawn Guo wrote: > > On Thu, Apr 21, 2016 at 11:45:20AM +0800, Dong Aisheng wrote: > >> On Fri, Jan 29, 2016 at 02:49:23PM -0800, Stefan Agner wrote: > >> > If a clock gets enabled early during boot time, it can lead to a PLL > >> > startup. The wait_lock function makes sure that the PLL is really > >> > stareted up before it gets used. However, the function sleeps which > >> > leads to scheduling and an error: > >> > bad: scheduling from the idle thread! > >> > ... > >> > > >> > Use udelay in case IRQ's are still disabled. > >> > > >> > Signed-off-by: Stefan Agner > >> > --- > >> > drivers/clk/imx/clk-pllv3.c | 5 ++++- > >> > 1 file changed, 4 insertions(+), 1 deletion(-) > >> > > >> > diff --git a/drivers/clk/imx/clk-pllv3.c b/drivers/clk/imx/clk-pllv3.c > >> > index c05c43d..b5ff561 100644 > >> > --- a/drivers/clk/imx/clk-pllv3.c > >> > +++ b/drivers/clk/imx/clk-pllv3.c > >> > @@ -63,7 +63,10 @@ static int clk_pllv3_wait_lock(struct clk_pllv3 *pll) > >> > break; > >> > if (time_after(jiffies, timeout)) > >> > break; > >> > - usleep_range(50, 500); > >> > + if (unlikely(irqs_disabled())) > >> > >> This causes a bit confusion that clk_pllv3_prepare is sleepable. > >> But this line indicates it's possible to be called in irq context. > >> Although it's only happened during kernel boot phase where irq is > >> still not enabled. > >> It seems schedule_debug() somehow did not catch it during early boot > >> phase. Maybe schedule guys can help explain. > >> > >> My question is if it's really worthy to introduce this confusion > >> to fix the issue since the delay is minor? > > > > I do not understand why it's confusing. The code already obviously > > indicates this is a special handling for cases where irq is still not > > enabled, rather than for irq context. > > > > The code itself has nothing telling it's a special handling for the > case where irq is > still not enabled. I think the following if-clause is telling that. if (unlikely(irqs_disabled())) > Even it tells, it may still cause confusing by adding complexity in > clk_pllv3_prepare() > which actually should be called in non-atomic context as it could sleep. I agree with you on that. > > The patch is to fix the "bad: scheduling from the idle thread!" warning > > rather than minimize the delay. Do you have an opinion on how to fix > > the warning? > > > > I just wonder maybe we could simply just using udelay(50) instead of > usleep_range(50, 500) to eliminate the confusing since it's minor cast. > What do you think of it? I'm fine with it. Since I haven't sent the patch to clk maintainers, I could replace Stefan's patch with yours, if you can send me a patch quickly. Shawn