Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752826Ab0FLFOY (ORCPT ); Sat, 12 Jun 2010 01:14:24 -0400 Received: from gate.crashing.org ([63.228.1.57]:35787 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751642Ab0FLFOX (ORCPT ); Sat, 12 Jun 2010 01:14:23 -0400 Subject: Re: [RFC,PATCH 1/2] Add a common struct clk From: Benjamin Herrenschmidt To: Lothar =?ISO-8859-1?Q?Wa=DFmann?= Cc: Uwe =?ISO-8859-1?Q?Kleine-K=F6nig?= , Jeremy Kerr , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Ben Dooks In-Reply-To: <19474.2817.333749.485028@ipc1.ka-ro> References: <1275636608.606606.450179637764.0.gpush@pororo> <201006111557.12249.jeremy.kerr@canonical.com> <19473.61547.684572.647641@ipc1.ka-ro> <201006111718.47426.jeremy.kerr@canonical.com> <19474.172.742782.972629@ipc1.ka-ro> <20100611095839.GC10894@pengutronix.de> <19474.2817.333749.485028@ipc1.ka-ro> Content-Type: text/plain; charset="UTF-8" Date: Sat, 12 Jun 2010 15:14:03 +1000 Message-ID: <1276319643.1962.181.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1142 Lines: 27 On Fri, 2010-06-11 at 12:08 +0200, Lothar Waßmann wrote: > Hi, > > > > > > Using a mutex in clk_enable()/clk_disable() is a bad idea, since that > > > > > makes it impossible to call those functions in interrupt context. > > IMHO if a device generates an irq its clock should already be on. This > > way you don't need to enable or disable a clock in irq context. > > > You may want to disable a clock in the IRQ handler. The VPU driver in > the Freescale BSP for i.MX51 does exactly this. > Anyway I don't see any reason for using a mutex here instead of > spin_lock_irq_save() as all other implementations do. Because you suddenly make it impossible to sleep inside enable/disable unless I'm mistaken about the implementation details. Some PLLs can need milliseconds to stabilize (especially if they need to be powered up first). Doing that with a lock held is a BAD IDEA. Cheers, Ben. -- 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/