[PATCH] ARM: OMAP2+: clockdomain: disabling unused clks

[Paul Walmsley]

On Fri, 9 Nov 2012, Paul Walmsley wrote:

> On Thu, 8 Nov 2012, Mike Turquette wrote:
> 
> > You're right.  In my rush I glossed over the clkdm decrement part.  In
> > light of the suspend/resume issues I'm not sure this approach is really
> > valid.  I think getting to the bottom of those issues will give the
> > final word.
> 
> What do you think about something like this?  It's still under test and 
> review here, but seems to avoid the warnings on 3530ES3 Beagle at least.
> 
> The usage of __clk_get_enable_count() in this code still seems like a hack 
> to me.  It would be better for the CCF to call a different clk_hw_ops 
> function pointer for the disable-unused-clocks case.  But if you agree, 
> and plan to fix this, or have some other cleaner fix in mind for the near 
> future, then something like this seems reasonable for the short term to 
> me.  What do you think?

Here's the patch.  The changes to clkdm_clk_disable() are the important 
ones, the rest can be ignored for the purposes of this review.


- Paul

From: Mike Turquette <mturquette at ti.com>
Date: Fri, 9 Nov 2012 11:28:42 -0700
Subject: [PATCH] ARM: OMAP2+: clockdomain: bypass clockdomain handling when
 disabling unused clks

The OMAP port to the common clk framework[1] resulted in spurious WARNs
while disable unused clocks.  This is due to _clkdm_clk_hwmod_disable
catching clkdm->usecount's with a value of zero.  Even less desirable it
would not allow the clkdm_clk_disable function pointer to get called due
to an early return of -ERANGE.

This patch adds a check for such a corner case by skipping the WARN and
early return in the event that clkdm->usecount and clk->enable_usecount
are both zero.  Presumably this could only happen during the check for
unused clocks at boot-time.

[1] http://article.gmane.org/gmane.linux.ports.arm.omap/88824

Signed-off-by: Mike Turquette <mturquette at ti.com>
[paul at pwsan.com: split the hwmod and clock disable cases; modified the
 code to skip the clockdomain handling during the disable-unused-clocks phase]
---
 arch/arm/mach-omap2/clockdomain.c |   91 ++++++++++++++++++++++---------------
 1 file changed, 54 insertions(+), 37 deletions(-)

diff --git a/arch/arm/mach-omap2/clockdomain.c b/arch/arm/mach-omap2/clockdomain.c
index 64e5046..1bd0ff0 100644
--- a/arch/arm/mach-omap2/clockdomain.c
+++ b/arch/arm/mach-omap2/clockdomain.c
@@ -22,6 +22,7 @@
 #include <linux/clk.h>
 #include <linux/limits.h>
 #include <linux/err.h>
+#include <linux/clk-private.h>
 
 #include <linux/io.h>
 
@@ -947,35 +948,6 @@ static int _clkdm_clk_hwmod_enable(struct clockdomain *clkdm)
 	return 0;
 }
 
-static int _clkdm_clk_hwmod_disable(struct clockdomain *clkdm)
-{
-	unsigned long flags;
-
-	if (!clkdm || !arch_clkdm || !arch_clkdm->clkdm_clk_disable)
-		return -EINVAL;
-
-	spin_lock_irqsave(&clkdm->lock, flags);
-
-	if (atomic_read(&clkdm->usecount) == 0) {
-		spin_unlock_irqrestore(&clkdm->lock, flags);
-		WARN_ON(1); /* underflow */
-		return -ERANGE;
-	}
-
-	if (atomic_dec_return(&clkdm->usecount) > 0) {
-		spin_unlock_irqrestore(&clkdm->lock, flags);
-		return 0;
-	}
-
-	arch_clkdm->clkdm_clk_disable(clkdm);
-	pwrdm_state_switch(clkdm->pwrdm.ptr);
-	spin_unlock_irqrestore(&clkdm->lock, flags);
-
-	pr_debug("clockdomain: %s: disabled\n", clkdm->name);
-
-	return 0;
-}
-
 /**
  * clkdm_clk_enable - add an enabled downstream clock to this clkdm
  * @clkdm: struct clockdomain *
@@ -1018,15 +990,39 @@ int clkdm_clk_enable(struct clockdomain *clkdm, struct clk *clk)
  */
 int clkdm_clk_disable(struct clockdomain *clkdm, struct clk *clk)
 {
-	/*
-	 * XXX Rewrite this code to maintain a list of enabled
-	 * downstream clocks for debugging purposes?
-	 */
+	unsigned long flags;
+	int force_disable = 0;
 
-	if (!clk)
+	if (!clkdm || !clk || !arch_clkdm || !arch_clkdm->clkdm_clk_disable)
 		return -EINVAL;
 
-	return _clkdm_clk_hwmod_disable(clkdm);
+	spin_lock_irqsave(&clkdm->lock, flags);
+
+	/* corner case: disabling unused clocks */
+	force_disable = (__clk_get_enable_count(clk) == 0) ? 1 : 0;
+	if (force_disable)
+		goto ccd_exit;
+
+	if (atomic_read(&clkdm->usecount) == 0) {
+		spin_unlock_irqrestore(&clkdm->lock, flags);
+		WARN_ON(1); /* underflow */
+		return -ERANGE;
+	}
+
+	if (atomic_dec_return(&clkdm->usecount) > 0) {
+		spin_unlock_irqrestore(&clkdm->lock, flags);
+		return 0;
+	}
+
+	arch_clkdm->clkdm_clk_disable(clkdm);
+	pwrdm_state_switch(clkdm->pwrdm.ptr);
+
+	pr_debug("clockdomain: %s: disabled\n", clkdm->name);
+
+ccd_exit:
+	spin_unlock_irqrestore(&clkdm->lock, flags);
+
+	return 0;
 }
 
 /**
@@ -1077,6 +1073,8 @@ int clkdm_hwmod_enable(struct clockdomain *clkdm, struct omap_hwmod *oh)
  */
 int clkdm_hwmod_disable(struct clockdomain *clkdm, struct omap_hwmod *oh)
 {
+	unsigned long flags;
+
 	/* The clkdm attribute does not exist yet prior OMAP4 */
 	if (cpu_is_omap24xx() || cpu_is_omap34xx())
 		return 0;
@@ -1086,9 +1084,28 @@ int clkdm_hwmod_disable(struct clockdomain *clkdm, struct omap_hwmod *oh)
 	 * downstream hwmods for debugging purposes?
 	 */
 
-	if (!oh)
+	if (!clkdm || !oh || !arch_clkdm || !arch_clkdm->clkdm_clk_disable)
 		return -EINVAL;
 
-	return _clkdm_clk_hwmod_disable(clkdm);
+	spin_lock_irqsave(&clkdm->lock, flags);
+
+	if (atomic_read(&clkdm->usecount) == 0) {
+		spin_unlock_irqrestore(&clkdm->lock, flags);
+		WARN_ON(1); /* underflow */
+		return -ERANGE;
+	}
+
+	if (atomic_dec_return(&clkdm->usecount) > 0) {
+		spin_unlock_irqrestore(&clkdm->lock, flags);
+		return 0;
+	}
+
+	arch_clkdm->clkdm_clk_disable(clkdm);
+	pwrdm_state_switch(clkdm->pwrdm.ptr);
+	spin_unlock_irqrestore(&clkdm->lock, flags);
+
+	pr_debug("clockdomain: %s: disabled\n", clkdm->name);
+
+	return 0;
 }
 
-- 
1.7.10.4