On Wed, Nov 30, 2011 at 06:20:50PM -0700, Paul Walmsley wrote: > 1. When a clock user calls clk_enable() on a clock, the clock framework > should prevent other users of the clock from changing the clock's rate. > This should persist until the clock user calls clk_disable() (but see also > #2 below). This will ensure that clock users can rely on the rate > returned by clk_get_rate(), as long as it's called between clk_enable() > and clk_disable(). And since the clock's rate is guaranteed to remain the > same during this time, code that cannot tolerate clock rate changes > without special handling (such as driver code for external I/O devices) > will work safely without further modification. So, if you have a PLL whose parent clock is not used by anything else. You want to program it to a certain rate. You call clk_disable() on the PLL clock. This walks up the tree and disables the parent. You then try to set the rate using clk_set_rate(). clk_set_rate() in this circumstance can't wait for the PLL to lock because it can't - there's no reference clock for it. You then call clk_enable(). The PLL now takes its time to lock. You can't sleep in clk_enable() because it might be called from atomic contexts, so you have to spin waiting for this. Overloading clk_disable/clk_enable in this way is a bad solution to this problem. -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
