Messages in this thread |  | | | Date | Sat, 22 Jan 2011 14:30:51 +0900 | | Subject | Re: Locking in the clk API | | From | Jassi Brar <> |
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On Sat, Jan 22, 2011 at 1:08 PM, Richard Zhao <linuxzsc@gmail.com> wrote: > On Fri, Jan 21, 2011 at 01:47:29PM +0900, Jassi Brar wrote: >> On Fri, Jan 21, 2011 at 9:09 AM, Jassi Brar <jassisinghbrar@gmail.com> wrote: >> > On Fri, Jan 21, 2011 at 4:08 AM, Russell King - ARM Linux >> > <linux@arm.linux.org.uk> wrote: >> >> On Thu, Jan 20, 2011 at 05:02:55PM +0000, Ben Dooks wrote: >> >>> If you want to make it so that each low-power mode has to work >> >>> out what PLLs need to be disabled and then re-enabled makes me >> >>> want to be sick. Hiding this stuff behind specific implementations >> >>> is a recipe for disaster. >> >> >> >> Why should systems which don't suffer from such problems be prevented >> >> from gaining power saving from turning off their clocks when devices >> >> are not being used (eg, the console serial port.) >> >> >> >> One solution to your root PLL issue would be to have a separate set of >> >> enable/disable API calls which get called at setup/release time (or >> >> whatever you'd like to call it) which can only be called from non-atomic >> >> context. Maybe clk_prepare() and clk_unprepare(). These functions >> >> should perform whatever is necessary to ensure that the clock source >> >> is available for use atomically when clk_enable() is called. >> >> >> >> So, in your case, clk_prepare() ensures that the root PLL is enabled, >> >> clk_unprepare() allows it to be turned off. >> >> >> >> In the case of a console driver, clk_prepare() can be called when we >> >> know the port will be used as a console. clk_enable() is then called >> >> before writing out the string, and clk_disable() after we've completely >> >> sent the last character. >> >> >> >> This allows the best of both worlds. We now have a clk_enable() which >> >> can be used to turn the clocks off through the clock tree up to the first >> >> non-atomic clock, and we also have a way to deal with those which need >> >> to sleep. So not only do "sleeping clock" implementations become possible >> >> but these "sleeping clock" implementations also get the opportunity to >> >> shutdown some of their clock tree with minimal latency for doing so. >> > >> > This is exactly what I suggested in my last post, except the console example. >> > Only to be a part of common clock api because it's not very safe to assume >> > future SoCs will have the same simple clock topologies that they have today. >> > >> > Not to mean to teach, but I hope you realize with more and more >> > device controller being crammed into ever shrinking SoCs, >> > clock would eventually have to be flexible in functionality >> > and complicated in hierarchy. Ben already gave examples >> > of Audio, MFC and Video controllers of latest Samsung SoCs. >> >> plus >> >> a) If only Samsung bsp implements the api, it would be impossible to >> share drivers, those that can be, with other platforms without nasty ifdef's. >> b) If the task of unification starts with only a particular platform made to >> implement a new api, the attempt kills its own purpose. > I'm not clear. Why does Samsung SoC go against clk_prepare/unprepare? > If its clock tree has many plls and device clock is not far away from plls and > may sleep, we may use prepare/unprepare to do actually clock enable/disable.
I am not against clk_prepare/unprepare. I rather suggest make it part of common clock API. Please read my last two posts again. -- 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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