[PATCH 4/5] ARM: imx: clk-gate2: Use post decrement for share_count

[shawn.guo@freescale.com (Shawn Guo)]

On Wed, Jul 02, 2014 at 01:52:56PM -0300, Fabio Estevam wrote:
> Hi Mike,
> 
> On Wed, Jul 2, 2014 at 12:29 PM, Mike Turquette <mturquette@linaro.org> wrote:
> 
> >> If share_count is 1 it means that someone else is using the clock and
> >> we can't disable it.
> >
> > Why do you keep track of share_count at all? Is the enable_count
> > bookkeeping within the clock framework insufficient for your needs?
> 
> What we are trying to handle here is the case when two clocks share
> the same clock gating bit.
> 
> Let's say clocks clk1 and clk2 share the same clock gating bit.
> 
> What we want to achieve are:
> 
> Scenario 1:
> 
> clk2 is disabled
> clk1 is enabled --> clock gate bit is set to 1
> clk1 is disabled --> clock gate bit is set to 0. As clk2 is disabled,
> it is OK to gate off the clock here
> 
> Scenario 2:
> 
> clk1 is enabled -> clock gate bit is set to 1
> clk2 is disabled -> clock gate bit cannot be set to 0 because clk1 is enabled

This never happens.  If clk2 is disabled by clk_disable() without being
enabled by clk_enable() beforehand, it returns from __clk_disable()
immediately due to hitting of the WARN below.

	if (WARN_ON(clk->enable_count == 0))
		return;

Shawn

> 
> We currently have arch/arm/mach-imx/clk-gate2.c and we are trying to
> fix it because the scenario 2 is not working.
> 
> I am wondering if we should just extend drivers/clk/clk-gate.c to
> handle shared clock instead of doing this in arch/arm/mach-imx?
> 
> What do you think?
> 
> Thanks,
> 
> Fabio Estevam