Russell King - ARM Linux [off-list ref] writes:

On Fri, Oct 09, 2015 at 10:57:35PM +0100, Mans Rullgard wrote:

quoted

This passes a data pointer specified in the sched_clock_register()
call to the read callback allowing simpler implementations thereof.

In this patch, existing uses of this interface are simply updated
with a null pointer.

This is a bad description.  It tells us what the patch is doing,
(which we can see by reading the patch) but not _why_.  Please include
information on why the change is necessary - describe what you are
trying to achieve.

Currently most of the callbacks use a global variable to store the
address of a counter register.  This has several downsides:

- Loading the address of a global variable can be more expensive than
  keeping a pointer next to the function pointer.

- It makes it impossible to have multiple instances of a driver call
  sched_clock_register() since the caller can't know which clock will
  win in the end.

- Many of the existing callbacks are practically identical and could be
  replaced with a common generic function if it had a pointer argument.

If I've missed something that makes this a stupid idea, please tell.

-- 
Måns Rullgård
mans@mansr.com