SPEAr: clk: Add Fractional Synthesizer clock

All SPEAr SoC's contain Fractional Synthesizers. Their Fout is derived from
following equations:

Fout = Fin / (2 * div) (division factor)
div is 17 bits:-
     0-13 (fractional part)
     14-16 (integer part)
     div is (16-14 bits).(13-0 bits) (in binary)

     Fout = Fin/(2 * div)
     Fout = ((Fin / 10000)/(2 * div)) * 10000
     Fout = (2^14 * (Fin / 10000)/(2^14 * (2 * div))) * 10000
     Fout = (((Fin / 10000) << 14)/(2 * (div << 14))) * 10000

div << 14 is simply 17 bit value written at register.

This patch adds in support for this type of clock.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Reviewed-by: Mike Turquette <mturquette@linaro.org>

1 files changed, 165 insertions, 0 deletions

diff --git a/drivers/clk/spear/clk-frac-synth.c b/drivers/clk/spear/clk-frac-synth.c
new file mode 100644
index 000000000000..4dbdb3fe18e0
--- /dev/null
+++ b/drivers/clk/spear/clk-frac-synth.c
@@ -0,0 +1,165 @@
+/*
+ * Copyright (C) 2012 ST Microelectronics
+ * Viresh Kumar <viresh.kumar@st.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ *
+ * Fractional Synthesizer clock implementation
+ */
+
+#define pr_fmt(fmt) "clk-frac-synth: " fmt
+
+#include <linux/clk-provider.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+#include <linux/err.h>
+#include "clk.h"
+
+#define DIV_FACTOR_MASK		0x1FFFF
+
+/*
+ * DOC: Fractional Synthesizer clock
+ *
+ * Fout from synthesizer can be given from below equation:
+ *
+ * Fout= Fin/2*div (division factor)
+ * div is 17 bits:-
+ *	0-13 (fractional part)
+ *	14-16 (integer part)
+ *	div is (16-14 bits).(13-0 bits) (in binary)
+ *
+ *	Fout = Fin/(2 * div)
+ *	Fout = ((Fin / 10000)/(2 * div)) * 10000
+ *	Fout = (2^14 * (Fin / 10000)/(2^14 * (2 * div))) * 10000
+ *	Fout = (((Fin / 10000) << 14)/(2 * (div << 14))) * 10000
+ *
+ * div << 14 simply 17 bit value written at register.
+ * Max error due to scaling down by 10000 is 10 KHz
+ */
+
+#define to_clk_frac(_hw) container_of(_hw, struct clk_frac, hw)
+
+static unsigned long frac_calc_rate(struct clk_hw *hw, unsigned long prate,
+		int index)
+{
+	struct clk_frac *frac = to_clk_frac(hw);
+	struct frac_rate_tbl *rtbl = frac->rtbl;
+
+	prate /= 10000;
+	prate <<= 14;
+	prate /= (2 * rtbl[index].div);
+	prate *= 10000;
+
+	return prate;
+}
+
+static long clk_frac_round_rate(struct clk_hw *hw, unsigned long drate,
+		unsigned long *prate)
+{
+	struct clk_frac *frac = to_clk_frac(hw);
+	int unused;
+
+	return clk_round_rate_index(hw, drate, *prate, frac_calc_rate,
+			frac->rtbl_cnt, &unused);
+}
+
+static unsigned long clk_frac_recalc_rate(struct clk_hw *hw,
+		unsigned long parent_rate)
+{
+	struct clk_frac *frac = to_clk_frac(hw);
+	unsigned long flags = 0;
+	unsigned int div = 1, val;
+
+	if (frac->lock)
+		spin_lock_irqsave(frac->lock, flags);
+
+	val = readl_relaxed(frac->reg);
+
+	if (frac->lock)
+		spin_unlock_irqrestore(frac->lock, flags);
+
+	div = val & DIV_FACTOR_MASK;
+
+	if (!div)
+		return 0;
+
+	parent_rate = parent_rate / 10000;
+
+	parent_rate = (parent_rate << 14) / (2 * div);
+	return parent_rate * 10000;
+}
+
+/* Configures new clock rate of frac */
+static int clk_frac_set_rate(struct clk_hw *hw, unsigned long drate,
+				unsigned long prate)
+{
+	struct clk_frac *frac = to_clk_frac(hw);
+	struct frac_rate_tbl *rtbl = frac->rtbl;
+	unsigned long flags = 0, val;
+	int i;
+
+	clk_round_rate_index(hw, drate, prate, frac_calc_rate, frac->rtbl_cnt,
+			&i);
+
+	if (frac->lock)
+		spin_lock_irqsave(frac->lock, flags);
+
+	val = readl_relaxed(frac->reg) & ~DIV_FACTOR_MASK;
+	val |= rtbl[i].div & DIV_FACTOR_MASK;
+	writel_relaxed(val, frac->reg);
+
+	if (frac->lock)
+		spin_unlock_irqrestore(frac->lock, flags);
+
+	return 0;
+}
+
+struct clk_ops clk_frac_ops = {
+	.recalc_rate = clk_frac_recalc_rate,
+	.round_rate = clk_frac_round_rate,
+	.set_rate = clk_frac_set_rate,
+};
+
+struct clk *clk_register_frac(const char *name, const char *parent_name,
+		unsigned long flags, void __iomem *reg,
+		struct frac_rate_tbl *rtbl, u8 rtbl_cnt, spinlock_t *lock)
+{
+	struct clk_init_data init;
+	struct clk_frac *frac;
+	struct clk *clk;
+
+	if (!name || !parent_name || !reg || !rtbl || !rtbl_cnt) {
+		pr_err("Invalid arguments passed");
+		return ERR_PTR(-EINVAL);
+	}
+
+	frac = kzalloc(sizeof(*frac), GFP_KERNEL);
+	if (!frac) {
+		pr_err("could not allocate frac clk\n");
+		return ERR_PTR(-ENOMEM);
+	}
+
+	/* struct clk_frac assignments */
+	frac->reg = reg;
+	frac->rtbl = rtbl;
+	frac->rtbl_cnt = rtbl_cnt;
+	frac->lock = lock;
+	frac->hw.init = &init;
+
+	init.name = name;
+	init.ops = &clk_frac_ops;
+	init.flags = flags;
+	init.parent_names = &parent_name;
+	init.num_parents = 1;
+
+	clk = clk_register(NULL, &frac->hw);
+	if (!IS_ERR_OR_NULL(clk))
+		return clk;
+
+	pr_err("clk register failed\n");
+	kfree(frac);
+
+	return NULL;
+}