From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mundt Date: Thu, 28 May 2009 19:34:58 +0000 Subject: Re: [PATCH] sched: Support current clocksource handling in fallback sched_clock(). Message-Id: <20090528193458.GA1122@linux-sh.org> List-Id: References: <1243527218.28705.35.camel@desktop> <1243528329.6645.77.camel@laptop> <20090528164011.GA30104@linux-sh.org> <1243529547.28705.43.camel@desktop> <20090528165816.GA31688@linux-sh.org> <1243532324.28705.75.camel@desktop> <20090528175341.GA32118@linux-sh.org> <1243534252.28705.86.camel@desktop> <20090528182730.GA32767@linux-sh.org> <1243537463.28705.94.camel@desktop> In-Reply-To: <1243537463.28705.94.camel@desktop> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Daniel Walker Cc: Peter Zijlstra , Thomas Gleixner , Linus Walleij , Ingo Molnar , Andrew Victor , Haavard Skinnemoen , Andrew Morton , linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, linux-arm-kernel@lists.arm.linux.org.uk, John Stultz On Thu, May 28, 2009 at 12:04:23PM -0700, Daniel Walker wrote: > On Fri, 2009-05-29 at 03:27 +0900, Paul Mundt wrote: > > > Ah, ok, I suppose I could have explained that better. There are a couple > > of different considerations really. The timer blocks are often in > > different clock and power domains, meaning that only certain ones can be > > used for wakeups. These tend not to be ideal for general use, and so we > > only switch to them when we have to. > > > > To make matters more convoluted, the availability of different timer > > channels on different CPUs will depend on current pin state, and more > > importantly, what sort of states we are able to achieve. It is not > > uncommon to have some of the pins required by these channels locked down > > by other drivers during regular operation, which we in turn need to > > unload before the pin state can be reconfigured and the timer can > > succeed, all which needs to happen before certain power state transitions > > can take place. We implement dynamic pinmux for most of the SH CPUs > > precisely to deal with these sorts of problems. In the case of some of > > the microcontrollers that are timer heavy and low on pincount, it is not > > uncommon to have upwards of 16 different functions per pin. > > I'm still a little confused how kernel modules fit in here.. Are you > saying a user would unload some certain driver which has a pin locked > down and prevents the clocksource from working. Then the user would load > the clocksource module which would now function, and that all would have > to happen in order to enter a certain power state? > Yes.