[PATCH 1/5] clk: sunxi-ng: prevent NKMP clocks from temporarily get higher freq

[Icenowy Zheng]

It seems that on newer SoCs (already observed on A33, H3), when setting
all NKMP factors at the same time, the multiplier get applied first,
then the divider get applied. In some situations (e.g. the multiplier
increased but the divider decreased), this will make the clock
frequency temporarily higher than both the original frequency and the
target frequency, which may lead to system hang due to PLL_CPU(X) clock
usually being a NKMP clock.

A comparsion between the old divider (M*P) and the new one is added, and
if the divider get smaller when changing clock, the multiplier will be
applied first, so that the clock won't go to a frequency higher than
normal.

The interval between applying the first group of factors and the second
group is based on experiments results on an Orange Pi Zero board.

Signed-off-by: Icenowy Zheng <icenowy@xxxxxxx>
---
 drivers/clk/sunxi-ng/ccu_nkmp.c | 76 +++++++++++++++++++++++++++++++++++------
 1 file changed, 65 insertions(+), 11 deletions(-)

diff --git a/drivers/clk/sunxi-ng/ccu_nkmp.c b/drivers/clk/sunxi-ng/ccu_nkmp.c
index e58c95787f94..5da77eb60335 100644
--- a/drivers/clk/sunxi-ng/ccu_nkmp.c
+++ b/drivers/clk/sunxi-ng/ccu_nkmp.c
@@ -9,6 +9,7 @@
  */
 
 #include <linux/clk-provider.h>
+#include <linux/delay.h>
 
 #include "ccu_gate.h"
 #include "ccu_nkmp.h"
@@ -130,12 +131,49 @@ static long ccu_nkmp_round_rate(struct clk_hw *hw, unsigned long rate,
 	return *parent_rate * _nkmp.n * _nkmp.k / (_nkmp.m * _nkmp.p);
 }
 
+static void ccu_nkmp_extract_factors(const struct ccu_nkmp *nkmp,
+				     struct _ccu_nkmp *_nkmp, u32 reg)
+{
+	_nkmp->n = ((reg >> nkmp->n.shift) & GENMASK(nkmp->n.width - 1, 0))
+		   + nkmp->n.offset;
+	_nkmp->k = ((reg >> nkmp->k.shift) & GENMASK(nkmp->k.width - 1, 0))
+		   + nkmp->k.offset;
+	_nkmp->m = ((reg >> nkmp->m.shift) & GENMASK(nkmp->m.width - 1, 0))
+		   + nkmp->m.offset;
+	_nkmp->p = 1 <<
+		   ((reg >> nkmp->p.shift) & GENMASK(nkmp->p.width - 1, 0));
+}
+
+static u32 ccu_nkmp_apply_multiplier(const struct ccu_nkmp *nkmp,
+				     const struct _ccu_nkmp *_nkmp, u32 reg)
+{
+	reg &= ~GENMASK(nkmp->n.width + nkmp->n.shift - 1, nkmp->n.shift);
+	reg &= ~GENMASK(nkmp->k.width + nkmp->k.shift - 1, nkmp->k.shift);
+
+	reg |= (_nkmp->n - nkmp->n.offset) << nkmp->n.shift;
+	reg |= (_nkmp->k - nkmp->k.offset) << nkmp->k.shift;
+
+	return reg;
+}
+
+static u32 ccu_nkmp_apply_divider(const struct ccu_nkmp *nkmp,
+				  const struct _ccu_nkmp *_nkmp, u32 reg)
+{
+	reg &= ~GENMASK(nkmp->m.width + nkmp->m.shift - 1, nkmp->m.shift);
+	reg &= ~GENMASK(nkmp->p.width + nkmp->p.shift - 1, nkmp->p.shift);
+
+	reg |= (_nkmp->m - nkmp->m.offset) << nkmp->m.shift;
+	reg |= ilog2(_nkmp->p) << nkmp->p.shift;
+
+	return reg;
+}
+
 static int ccu_nkmp_set_rate(struct clk_hw *hw, unsigned long rate,
 			   unsigned long parent_rate)
 {
 	struct ccu_nkmp *nkmp = hw_to_ccu_nkmp(hw);
-	struct _ccu_nkmp _nkmp;
-	unsigned long flags;
+	struct _ccu_nkmp _nkmp, _nkmp_old;
+	unsigned long flags, old_mp, mp;
 	u32 reg;
 
 	_nkmp.min_n = nkmp->n.min ?: 1;
@@ -152,17 +190,33 @@ static int ccu_nkmp_set_rate(struct clk_hw *hw, unsigned long rate,
 	spin_lock_irqsave(nkmp->common.lock, flags);
 
 	reg = readl(nkmp->common.base + nkmp->common.reg);
-	reg &= ~GENMASK(nkmp->n.width + nkmp->n.shift - 1, nkmp->n.shift);
-	reg &= ~GENMASK(nkmp->k.width + nkmp->k.shift - 1, nkmp->k.shift);
-	reg &= ~GENMASK(nkmp->m.width + nkmp->m.shift - 1, nkmp->m.shift);
-	reg &= ~GENMASK(nkmp->p.width + nkmp->p.shift - 1, nkmp->p.shift);
 
-	reg |= (_nkmp.n - nkmp->n.offset) << nkmp->n.shift;
-	reg |= (_nkmp.k - nkmp->k.offset) << nkmp->k.shift;
-	reg |= (_nkmp.m - nkmp->m.offset) << nkmp->m.shift;
-	reg |= ilog2(_nkmp.p) << nkmp->p.shift;
+	ccu_nkmp_extract_factors(nkmp, &_nkmp_old, reg);
+
+	old_mp = _nkmp_old.m * _nkmp_old.p;
+	mp = _nkmp.m * _nkmp.p;
+
+	if (mp > old_mp) {
+		reg = ccu_nkmp_apply_divider(nkmp, &_nkmp, reg);
+		writel(reg, nkmp->common.base + nkmp->common.reg);
+
+		/*
+		 * This value is decided by experiment results on an
+		 * Allwinner H2+ board (Orange Pi Zero).
+		 */
+		udelay(500);
 
-	writel(reg, nkmp->common.base + nkmp->common.reg);
+		reg = ccu_nkmp_apply_multiplier(nkmp, &_nkmp, reg);
+		writel(reg, nkmp->common.base + nkmp->common.reg);
+	} else {
+		reg = ccu_nkmp_apply_multiplier(nkmp, &_nkmp, reg);
+		writel(reg, nkmp->common.base + nkmp->common.reg);
+
+		udelay(500);
+
+		reg = ccu_nkmp_apply_divider(nkmp, &_nkmp, reg);
+		writel(reg, nkmp->common.base + nkmp->common.reg);
+	}
 
 	spin_unlock_irqrestore(nkmp->common.lock, flags);
 
-- 
2.12.2