Messages in this thread | | | Date | Sat, 8 Jan 2011 14:15:21 +0100 | From | Sascha Hauer <> | Subject | Re: [PATCH 1/2] Add a common struct clk |
| |
Hi Jeremy,
On Wed, Jan 05, 2011 at 11:51:02AM +0800, Jeremy Kerr wrote: > We currently have ~21 definitions of struct clk in the ARM architecture, > each defined on a per-platform basis. This makes it difficult to define > platform- (or architecture-) independent clock sources without making > assumptions about struct clk, and impossible to compile two > platforms with different struct clks into a single image. > > This change is an effort to unify struct clk where possible, by defining > a common struct clk, containing a set of clock operations. Different > clock implementations can set their own operations, and have a standard > interface for generic code. The callback interface is exposed to the > kernel proper, while the clock implementations only need to be seen by > the platform internals. > > This allows us to share clock code among platforms, and makes it > possible to dynamically create clock devices in platform-independent > code. > > Platforms can enable the generic struct clock through > CONFIG_USE_COMMON_STRUCT_CLK. In this case, the clock infrastructure > consists of a common struct clk: > > struct clk { > const struct clk_ops *ops; > unsigned int enable_count; > int flags; > union { > struct mutex mutex; > spinlock_t spinlock; > } lock; > };
I'm currently thinking about how to get the locking right with this approach. In the current i.MX implementation we have a global lock which protects the clock enable counter and also the register accesses in the clock code. With the common struct clock we have a lock per clock which only protects the enable counter, so we have to introduce a second lock to protect the register accesses. The problem comes with nested calls to for example clk_enable which happens when the parent clock gets enabled. currently we do this with clk->enable(clk->parent) which results in an unlocked clk_enable of the parent. With common struct clk we would have to call clk_enable(clk_get_parent(clk) which results in taking the lock a second time. Any ideas how to solve this?
Sascha
-- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
| |