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SubjectRe: [PATCH/RFC 2.6.17-rc4-git] clk_must_disable()
Date
On Tuesday 16 May 2006 5:39 pm, David Brownell wrote:
> This defines a new optional clock API ... comments?

Well, nobody reported any down-side to this, and the up-side is that
having this kind of API (and a platform's implementation thereof)
finally makes it possible to let USB controllers properly issue
wakeup events on typical embedded hardware.

So I'll be submitting this for 2.6.18 soon, and at91rm9200 platform
updates to make clk_must_disable(clk32k) replace the current platform
private at91_suspend_entering_slow_clock() call in the USB and serial
drivers. When other platforms add support for more of their different
hardware sleep states, and implement, their USB host and peripheral
controller drivers can be updated accordingly.

- Dave



> In implementation terms, the platform's pm_ops.prepare() can record the
> target system state, and its implementation of this method would know
> thinks like "STR turns off those two PLLs and their derived clocks",
> while "standby leaves those PLLs on".
>
> Alternate PM approaches -- DPM, operating points, whatever -- could have
> their own internal representations of these constraints, but drivers would
> only need this one API call to check them from suspend() callbacks.
>
> - Dave
>
>
> ------------------------- SNIP!
>
> This patch adds a clk_must_disable() operation, exposing clock constraints
> that often distinguish system power states. Systems with such constraints
> include ones using ARM-based AT91, OMAP, and PXA chips. The new operation
> lets driver methods check those constraints.
>
> A common benefit to leaving some device clocks enabled is that a suspended
> device may then be able to issue system wakeup events. RS232, USB, Ethernet,
> and other drivers can use driver model wakeup flags to trade off between the
> lowest power "full off" states and more functional wakeup-enabled states,
> as configured through sysfs.
>
> Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
>
>
> --- at91-pre2.orig/include/linux/clk.h 2006-05-15 10:07:24.000000000 -0700
> +++ at91-pre2/include/linux/clk.h 2006-05-15 10:41:15.000000000 -0700
> @@ -121,4 +121,24 @@ int clk_set_parent(struct clk *clk, stru
> */
> struct clk *clk_get_parent(struct clk *clk);
>
> +/**
> + * clk_must_disable - report whether a clock's users must disable it
> + * @clk: one node in the clock tree
> + *
> + * This routine returns true only if the upcoming system state requires
> + * disabling the specified clock.
> + *
> + * It's common for platform power states to constrain certain clocks (and
> + * their descendants) to be unavailable, while other states allow that
> + * clock to be active. A platform's power states often include an "all on"
> + * mode; system wide sleep states like "standby" or "suspend-to-RAM"; and
> + * operating states which sacrifice functionality for lower power usage.
> + *
> + * The constraint value is commonly tested in device driver suspend(), to
> + * leave clocks active if they are needed for features like wakeup events.
> + * On platforms that support reduced functionality operating states, the
> + * constraint may also need to be tested during resume() and probe() calls.
> + */
> +int clk_must_disable(struct clk *clk);
> +
> #endif
>
-
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