1 files changed, 86 insertions, 0 deletions
diff --git a/drivers/clk/spacemit/ccu_ddn.c b/drivers/clk/spacemit/ccu_ddn.c
new file mode 100644
index 000000000000..5b16e273bee5
--- /dev/null
+++ b/drivers/clk/spacemit/ccu_ddn.c
@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2024 SpacemiT Technology Co. Ltd
+ * Copyright (c) 2024-2025 Haylen Chu <heylenay@4d2.org>
+ *
+ * DDN stands for "Divider Denominator Numerator", it's M/N clock with a
+ * constant x2 factor. This clock hardware follows the equation below,
+ *
+ *	      numerator       Fin
+ *	2 * ------------- = -------
+ *	     denominator      Fout
+ *
+ * Thus, Fout could be calculated with,
+ *
+ *		Fin	denominator
+ *	Fout = ----- * -------------
+ *		 2	 numerator
+ */
+
+#include <linux/clk-provider.h>
+#include <linux/rational.h>
+
+#include "ccu_ddn.h"
+
+static unsigned long ccu_ddn_calc_rate(unsigned long prate, unsigned long num,
+				       unsigned long den, unsigned int pre_div)
+{
+	return prate * den / pre_div / num;
+}
+
+static unsigned long ccu_ddn_calc_best_rate(struct ccu_ddn *ddn,
+					    unsigned long rate, unsigned long prate,
+					    unsigned long *num, unsigned long *den)
+{
+	rational_best_approximation(rate, prate / ddn->pre_div,
+				    ddn->den_mask >> ddn->den_shift,
+				    ddn->num_mask >> ddn->num_shift,
+				    den, num);
+	return ccu_ddn_calc_rate(prate, *num, *den, ddn->pre_div);
+}
+
+static int ccu_ddn_determine_rate(struct clk_hw *hw,
+				  struct clk_rate_request *req)
+{
+	struct ccu_ddn *ddn = hw_to_ccu_ddn(hw);
+	unsigned long num, den;
+
+	req->rate = ccu_ddn_calc_best_rate(ddn, req->rate,
+					   req->best_parent_rate, &num, &den);
+
+	return 0;
+}
+
+static unsigned long ccu_ddn_recalc_rate(struct clk_hw *hw, unsigned long prate)
+{
+	struct ccu_ddn *ddn = hw_to_ccu_ddn(hw);
+	unsigned int val, num, den;
+
+	val = ccu_read(&ddn->common, ctrl);
+
+	num = (val & ddn->num_mask) >> ddn->num_shift;
+	den = (val & ddn->den_mask) >> ddn->den_shift;
+
+	return ccu_ddn_calc_rate(prate, num, den, ddn->pre_div);
+}
+
+static int ccu_ddn_set_rate(struct clk_hw *hw, unsigned long rate,
+			    unsigned long prate)
+{
+	struct ccu_ddn *ddn = hw_to_ccu_ddn(hw);
+	unsigned long num, den;
+
+	ccu_ddn_calc_best_rate(ddn, rate, prate, &num, &den);
+
+	ccu_update(&ddn->common, ctrl,
+		   ddn->num_mask | ddn->den_mask,
+		   (num << ddn->num_shift) | (den << ddn->den_shift));
+
+	return 0;
+}
+
+const struct clk_ops spacemit_ccu_ddn_ops = {
+	.recalc_rate	= ccu_ddn_recalc_rate,
+	.determine_rate = ccu_ddn_determine_rate,
+	.set_rate	= ccu_ddn_set_rate,
+};