lkml.org 
[lkml]   [2011]   [Jan]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [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 |


\
 
 \ /
  Last update: 2011-01-08 14:17    [W:0.640 / U:0.272 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site