Messages in this thread |  | | | Date | Wed, 25 May 2011 10:08:51 +0800 | | From | Richard Zhao <> | | Subject | Re: [PATCH 0/4] Add a generic struct clk |
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On Tue, May 24, 2011 at 10:52:53AM -0700, Colin Cross wrote: > On Tue, May 24, 2011 at 10:22 AM, Richard Zhao <linuxzsc@gmail.com> wrote: > > On Mon, May 23, 2011 at 04:12:24PM -0700, Colin Cross wrote: > >> On Fri, May 20, 2011 at 12:27 AM, Jeremy Kerr <jeremy.kerr@canonical.com> wrote: > >> > [This series was originally titled 'Add a common struct clk', but > >> > the goals have changed since that first set of patches. We're now aiming > >> > for a more complete generic clock infrastructure, rather than just > >> > abstracting struct clk] > >> > > >> > [This series still needs work, see the TODO section below] > >> > > >> > [Totally RFC at the moment] > >> > > >> > Hi all, > >> > > >> > These patches are an attempt to allow platforms to share clock code. At > >> > present, the definitions of 'struct clk' are local to platform code, > >> > which makes allocating and initialising cross-platform clock sources > >> > difficult, and makes it impossible to compile a single image containing > >> > support for two ARM platforms with different struct clks. > >> > > >> > The three patches are for the architecture-independent kernel code, > >> > introducing the common clk infrastructure. The changelog for the first > >> > patch includes details about the new clock definitions. > >> > > >> > The second patch implements clk_set_rate, and in doing so adds > >> > functionality to walk the clock tree in both directions. > >> > > >> > clk_set_parent is left unimplemented, see TODO below for why. > >> > > >> > The third and fourth patches provide some basic clocks (fixed-rate and > >> > gated), mostly to serve as an example of the hardware implementation. > >> > I'm intending to later provide similar base clocks for mux and divider > >> > hardware clocks. > >> > > >> > Many thanks to the following for their input: > >> > * Benjamin Herrenschmidt <benh@kernel.crashing.org> > >> > * Thomas Gleixner <tglx@linutronix.de> > >> > * Ben Dooks <ben-linux@fluff.org> > >> > * Baruch Siach <baruch@tkos.co.il> > >> > * Russell King <linux@arm.linux.org.uk> > >> > * Uwe Kleine-König <u.kleine-koenig@pengutronix.de> > >> > * Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com> > >> > * Vincent Guittot <vincent.guittot@linaro.org> > >> > * Sascha Hauer <s.hauer@pengutronix.de> > >> > * Ryan Mallon <ryan@bluewatersys.com> > >> > * Colin Cross <ccross@google.com> > >> > * Jassi Brar <jassisinghbrar@gmail.com> > >> > * Saravana Kannan <skannan@codeaurora.org> > >> > >> I have a similar set of patches I was working on that handles a little > >> more of the common code than these. I can post them if you want, but > >> for now I'll just point out where I had different ideas, and not muddy > >> the waters with conflicting patches. > >> > >> > TODO: > >> > > >> > * Need to figure out the locking around clk_set_parent. Changing the in-kernel > >> > clock topology requires acquiring both the mutex (to prevent against races > >> > with clk_prepare, which may propagate to the parent clock) and the spinlock > >> > (to prevent the same race with clk_enable). > >> > > >> > However, we should also be changing the hardware clock topology in sync with > >> > the in-kernel clock topology, which would imply that both locks *also* need > >> > to be held while updating the parent in the hardware (ie, in > >> > clk_hw_ops->set_parent) too. However, I believe some platform clock > >> > implementations may require this callback to be able to sleep. Comments? > >> > >> This sequence is the best I could come up with without adding a > >> temporary 2nd parent: > >> 1. lock prepare mutex > > Maybe tell child clocks "I'm going to change clock rate, please stop work if needed" > >> 2. call prepare on the new parent if prepare_count > 0 > >> 3. lock the enable spinlock > >> 4. call enable on the new parent if enable_count > 0 > >> 5. change the parent pointer to the new parent > >> 6. unlock the spinlock > >> 7. call the set_parent callback > > Why do it need to sleep if it only set some hw registers? > > Most implementations don't, and I would be fine with saying > clk_set_parent sleeps, but the set_parent op does not, but that > prevents clock chips on sleeping busses like i2c. So it worth to involve a flag here, which says hw_ops may sleep. At least for on-SoC clocks, we don't need to take risk. > > >> 8. lock the enable spinlock > >> 9. call disable on the old parent iff you called enable on the new > >> parent (enable_count may have changed) > >> 10. unlock the enable spinlock > >> 11. call unprepare on the old parent if prepare_count > > propagate rate here and also tell child clocks "rate changed already, change your > > parameters and go on to work". > > Yes, propagate rate is needed. > > >> 12. unlock prepare mutex > >> > >> The only possible problem I see is that if a clock starts disabled at > >> step 1., and clk_enable is called on it between steps 6 and 7, > >> clk_enable will return having enabled the new parent, but the clock is > >> still running off the old parent. As soon as the clock gets switched > >> to the new parent, the clock will be properly enabled. I don't see > >> this as a huge problem - calling clk_set_parent on a clock while it is > >> enabled may not even work without causing glitches on some platforms. > > some do be glitch free, especially for cpu clock parents. > >> > >> I guess the only way around it would be to store a temporary > >> "new_parent" pointer between steps 5 and 9, and have > >> clk_enable/disable operate on both the current parent and the new > >> parent. They would also need to refcount the extra enables separately > >> to undo on the old parent. > >> > >> > * tglx and I have been discussing different ways of passing clock information > >> > to the clock hardware implementation. I'm proposing providing a base 'struct > >> > clk_hw', which implementations subclass by wrapping in their own structure > >> > (or one of a set of simple 'library' structures, like clk_hw_mux or > >> > clk_hw_gate). The clk_hw base is passed as the first argument to all > >> > clk_hw_ops callbacks. > >> > > >> > tglx's plan is to create a separate struct clk_hwdata, which contains a > >> > union of base data structures for common clocks: div, mux, gate, etc. The > >> > ops callbacks are passed a clk_hw, plus a clk_hwdata, and most of the base > >> > hwdata fields are handled within the core clock code. This means less > >> > encapsulation of clock implementation logic, but more coverage of > >> > clock basics through the core code. > >> > >> I don't think they should be a union, I think there should be 3 > >> separate private datas, and three sets of clock ops, for the three > >> different types of clock blocks: rate changers (dividers and plls), > >> muxes, and gates. These blocks are very often combined - a device > >> clock often has a mux and a divider, and clk_set_parent and > >> clk_set_rate on the same struct clk both need to work. > >> > >> > tglx, could you send some details about your approach? I'm aiming to refine > >> > this series with the good bits from each technique. > >> > > >> > * The clock registration code probably needs work. This is the domain > >> > of the platform/board maintainers, any wishes here? > > When clock init, data in struct clk may not be synced with hw registers. After > > enabled minimal needed clk (cpu, core bus etc), we need sync the whole tree, > > disable zero enable_count clocks, set correct .rate ... . The sync function > > is also common code, right? but not have to be called all times I think. > > I believe each clock is synced with its hardware during clk_register > by calling the recalc_rate and get_parent callbacks. so how to sync gate bits? Let subarch to set registers directly or clk_enable and clk_disable to make sure clk is disabled? Neither way is good I think.
Thanks Richard > > > Thanks > > Richard > >> > > >> > Cheers, > >> > > >> > > >> > Jeremy > >> > > >> > -- > >> > > >> > --- > >> > Jeremy Kerr (4): > >> > clk: Add a generic clock infrastructure > >> > clk: Implement clk_set_rate > >> > clk: Add fixed-rate clock > >> > clk: Add simple gated clock > >> > > >> > -- > >> > 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/ > >> > > >> > >> _______________________________________________ > >> linux-arm-kernel mailing list > >> linux-arm-kernel@lists.infradead.org > >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > -- 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/
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