[PATCH] clk: fix apss cpu overclocking

[John Crispin <john@phrozen.org>]

From: Christian Lamparter <chunkeey@googlemail.com>

There's an interaction issue between the clk changes:"
clk: qcom: ipq4019: Add the apss cpu pll divider clock node
clk: qcom: ipq4019: remove fixed clocks and add pll clocks
" and the cpufreq-dt.

cpufreq-dt is now spamming the kernel-log with the following:

[ 1099.190658] cpu cpu0: dev_pm_opp_set_rate: failed to find current OPP
for freq 761142857 (-34)

This only happens on certain devices like the Compex WPJ428
and AVM FritzBox!4040. However, other devices like the Asus
RT-AC58U and Meraki MR33 work just fine.

The issue stem from the fact that all higher CPU-Clocks
are achieved by switching the clock-parent to the P_DDRPLLAPSS
(ddrpllapss). Which is set by Qualcomm's proprietary bootcode
as part of the DDR calibration.

For example, the FB4040 uses 256 MiB Nanya NT5CC128M16IP clocked
at round 533 MHz (ddrpllsdcc = 190285714 Hz).

whereas the 128 MiB Nanya NT5CC64M16GP-DI in the ASUS RT-AC58U is
clocked at a slightly higher 537 MHz ( ddrpllsdcc = 192000000 Hz).

This patch attempts to fix the issue by modifying
clk_cpu_div_round_rate(), clk_cpu_div_set_rate(), clk_cpu_div_recalc_rate()
to use a new qcom_find_freq_close() function, which returns the closest
matching frequency, instead of the next higher. This way, the SoC in
the FB4040 (with its max clock speed of 710.4 MHz) will no longer
try to overclock to 761 MHz.

Fixes: d83dcacea18 ("clk: qcom: ipq4019: Add the apss cpu pll divider clock node")
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: John Crispin <john@phrozen.org>
---
 drivers/clk/qcom/gcc-ipq4019.c | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/qcom/gcc-ipq4019.c b/drivers/clk/qcom/gcc-ipq4019.c
index 46cb256b4aa2..4ec43f7d2e52 100644
--- a/drivers/clk/qcom/gcc-ipq4019.c
+++ b/drivers/clk/qcom/gcc-ipq4019.c
@@ -1253,6 +1253,29 @@ static const struct clk_fepll_vco gcc_fepll_vco = {
 	.reg = 0x2f020,
 };
 
+
+const struct freq_tbl *qcom_find_freq_close(const struct freq_tbl *f,
+					     unsigned long rate)
+{
+	const struct freq_tbl *last = NULL;
+
+	for ( ; f->freq; f++) {
+		if (rate == f->freq)
+			return f;
+
+		if (f->freq > rate) {
+			if (!last ||
+			   (f->freq - rate) < (rate - last->freq))
+				return f;
+			else
+				return last;
+		}
+		last = f;
+	}
+
+	return last;
+}
+
 /*
  * Round rate function for APSS CPU PLL Clock divider.
  * It looks up the frequency table and returns the next higher frequency
@@ -1265,7 +1288,7 @@ static long clk_cpu_div_round_rate(struct clk_hw *hw, unsigned long rate,
 	struct clk_hw *p_hw;
 	const struct freq_tbl *f;
 
-	f = qcom_find_freq(pll->freq_tbl, rate);
+	f = qcom_find_freq_close(pll->freq_tbl, rate);
 	if (!f)
 		return -EINVAL;
 
@@ -1288,7 +1311,7 @@ static int clk_cpu_div_set_rate(struct clk_hw *hw, unsigned long rate,
 	u32 mask;
 	int ret;
 
-	f = qcom_find_freq(pll->freq_tbl, rate);
+	f = qcom_find_freq_close(pll->freq_tbl, rate);
 	if (!f)
 		return -EINVAL;
 
@@ -1315,6 +1338,7 @@ static unsigned long
 clk_cpu_div_recalc_rate(struct clk_hw *hw,
 			unsigned long parent_rate)
 {
+	const struct freq_tbl *f;
 	struct clk_fepll *pll = to_clk_fepll(hw);
 	u32 cdiv, pre_div;
 	u64 rate;
@@ -1335,7 +1359,11 @@ clk_cpu_div_recalc_rate(struct clk_hw *hw,
 	rate = clk_fepll_vco_calc_rate(pll, parent_rate) * 2;
 	do_div(rate, pre_div);
 
-	return rate;
+	f = qcom_find_freq_close(pll->freq_tbl, rate);
+	if (!f)
+		return rate;
+
+	return f->freq;
 };
 
 static const struct clk_ops clk_regmap_cpu_div_ops = {
-- 
2.11.0