clk: Add a bypass clock for K210

This is a small driver to do a software bypass of a clock if hardware
bypass is not working. I have tried to write this in a generic fashion, so
that it could be potentially broken out of the kendryte code at some future
date. For the K210, it is used to have aclk bypass pll0 and use in0 instead
so that the CPU keeps on working.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
CC: Lukasz Majewski <lukma@denx.de>

drivers/clk/kendryte/Makefile

@@ -1 +1 @@
-obj-y += pll.o
+obj-y += bypass.o pll.o

drivers/clk/kendryte/bypass.c

@@ -0,0 +1,270 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020 Sean Anderson <seanga2@gmail.com>
+ */
+
+#define LOG_CATEGORY UCLASS_CLK
+#include <kendryte/bypass.h>
+
+#include <clk-uclass.h>
+#include <linux/clk-provider.h>
+#include <linux/err.h>
+#include <log.h>
+
+#define CLK_K210_BYPASS "k210_clk_bypass"
+
+/*
+ * This is a small driver to do a software bypass of a clock if hardware bypass
+ * is not working. I have tried to write this in a generic fashion, so that it
+ * could be potentially broken out of the kendryte code at some future date.
+ *
+ * Say you have the following clock configuration
+ *
+ * +---+ +---+
+ * |osc| |pll|
+ * +---+ +---+
+ *         ^
+ *        /|
+ *       / |
+ *      /  |
+ *     /   |
+ *    /    |
+ * +---+ +---+
+ * |clk| |clk|
+ * +---+ +---+
+ *
+ * But the pll does not have a bypass, so when you configure the pll, the
+ * configuration needs to change to look like
+ *
+ * +---+ +---+
+ * |osc| |pll|
+ * +---+ +---+
+ *   ^
+ *   |\
+ *   | \
+ *   |  \
+ *   |   \
+ *   |    \
+ * +---+ +---+
+ * |clk| |clk|
+ * +---+ +---+
+ *
+ * To set this up, create a bypass clock with bypassee=pll and alt=osc. When
+ * creating the child clocks, set their parent to the bypass clock. After
+ * creating all the children, call k210_bypass_setchildren().
+ */
+
+static int k210_bypass_dobypass(struct k210_bypass *bypass)
+{
+	int ret, i;
+
+	/*
+	 * If we already have saved parents, then the children are already
+	 * bypassed
+	 */
+	if (bypass->child_count && bypass->saved_parents[0])
+		return 0;
+
+	for (i = 0; i < bypass->child_count; i++) {
+		struct clk *child = bypass->children[i];
+		struct clk *parent = clk_get_parent(child);
+
+		if (IS_ERR(parent)) {
+			for (; i; i--)
+				bypass->saved_parents[i] = NULL;
+			return PTR_ERR(parent);
+		}
+		bypass->saved_parents[i] = parent;
+	}
+
+	for (i = 0; i < bypass->child_count; i++) {
+		struct clk *child = bypass->children[i];
+
+		ret = clk_set_parent(child, bypass->alt);
+		if (ret) {
+			for (; i; i--)
+				clk_set_parent(bypass->children[i],
+					       bypass->saved_parents[i]);
+			for (i = 0; i < bypass->child_count; i++)
+				bypass->saved_parents[i] = NULL;
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int k210_bypass_unbypass(struct k210_bypass *bypass)
+{
+	int err, ret, i;
+
+	if (!bypass->child_count && !bypass->saved_parents[0]) {
+		log_warning("Cannot unbypass children; dobypass not called first\n");
+		return 0;
+	}
+
+	ret = 0;
+	for (i = 0; i < bypass->child_count; i++) {
+		err = clk_set_parent(bypass->children[i],
+				     bypass->saved_parents[i]);
+		if (err)
+			ret = err;
+		bypass->saved_parents[i] = NULL;
+	}
+	return ret;
+}
+
+static ulong k210_bypass_get_rate(struct clk *clk)
+{
+	struct k210_bypass *bypass = to_k210_bypass(clk);
+	const struct clk_ops *ops = bypass->bypassee_ops;
+
+	if (ops->get_rate)
+		return ops->get_rate(bypass->bypassee);
+	else
+		return clk_get_parent_rate(bypass->bypassee);
+}
+
+static ulong k210_bypass_set_rate(struct clk *clk, unsigned long rate)
+{
+	int ret;
+	struct k210_bypass *bypass = to_k210_bypass(clk);
+	const struct clk_ops *ops = bypass->bypassee_ops;
+
+	/* Don't bother bypassing if we aren't going to set the rate */
+	if (!ops->set_rate)
+		return k210_bypass_get_rate(clk);
+
+	ret = k210_bypass_dobypass(bypass);
+	if (ret)
+		return ret;
+
+	ret = ops->set_rate(bypass->bypassee, rate);
+	if (ret < 0)
+		return ret;
+
+	return k210_bypass_unbypass(bypass);
+}
+
+static int k210_bypass_set_parent(struct clk *clk, struct clk *parent)
+{
+	struct k210_bypass *bypass = to_k210_bypass(clk);
+	const struct clk_ops *ops = bypass->bypassee_ops;
+
+	if (ops->set_parent)
+		return ops->set_parent(bypass->bypassee, parent);
+	else
+		return -ENOTSUPP;
+}
+
+/*
+ * For these next two functions, do the bypassing even if there is no
+ * en-/-disable function, since the bypassing itself can be observed in between
+ * calls.
+ */
+static int k210_bypass_enable(struct clk *clk)
+{
+	int ret;
+	struct k210_bypass *bypass = to_k210_bypass(clk);
+	const struct clk_ops *ops = bypass->bypassee_ops;
+
+	ret = k210_bypass_dobypass(bypass);
+	if (ret)
+		return ret;
+
+	if (ops->enable)
+		ret = ops->enable(bypass->bypassee);
+	else
+		ret = 0;
+	if (ret)
+		return ret;
+
+	return k210_bypass_unbypass(bypass);
+}
+
+static int k210_bypass_disable(struct clk *clk)
+{
+	int ret;
+	struct k210_bypass *bypass = to_k210_bypass(clk);
+	const struct clk_ops *ops = bypass->bypassee_ops;
+
+	ret = k210_bypass_dobypass(bypass);
+	if (ret)
+		return ret;
+
+	if (ops->disable)
+		return ops->disable(bypass->bypassee);
+	else
+		return 0;
+}
+
+static const struct clk_ops k210_bypass_ops = {
+	.get_rate = k210_bypass_get_rate,
+	.set_rate = k210_bypass_set_rate,
+	.set_parent = k210_bypass_set_parent,
+	.enable = k210_bypass_enable,
+	.disable = k210_bypass_disable,
+};
+
+int k210_bypass_set_children(struct clk *clk, struct clk **children,
+			     size_t child_count)
+{
+	struct k210_bypass *bypass = to_k210_bypass(clk);
+
+	kfree(bypass->saved_parents);
+	if (child_count) {
+		bypass->saved_parents =
+			kcalloc(child_count, sizeof(struct clk *), GFP_KERNEL);
+		if (!bypass->saved_parents)
+			return -ENOMEM;
+	}
+	bypass->child_count = child_count;
+	bypass->children = children;
+
+	return 0;
+}
+
+struct clk *k210_register_bypass_struct(const char *name,
+					const char *parent_name,
+					struct k210_bypass *bypass)
+{
+	int ret;
+	struct clk *clk;
+
+	clk = &bypass->clk;
+
+	ret = clk_register(clk, CLK_K210_BYPASS, name, parent_name);
+	if (ret)
+		return ERR_PTR(ret);
+
+	bypass->bypassee->dev = clk->dev;
+	return clk;
+}
+
+struct clk *k210_register_bypass(const char *name, const char *parent_name,
+				 struct clk *bypassee,
+				 const struct clk_ops *bypassee_ops,
+				 struct clk *alt)
+{
+	struct clk *clk;
+	struct k210_bypass *bypass;
+
+	bypass = kzalloc(sizeof(*bypass), GFP_KERNEL);
+	if (!bypass)
+		return ERR_PTR(-ENOMEM);
+
+	bypass->bypassee = bypassee;
+	bypass->bypassee_ops = bypassee_ops;
+	bypass->alt = alt;
+
+	clk = k210_register_bypass_struct(name, parent_name, bypass);
+	if (IS_ERR(clk))
+		kfree(bypass);
+	return clk;
+}
+
+U_BOOT_DRIVER(k210_bypass) = {
+	.name	= CLK_K210_BYPASS,
+	.id	= UCLASS_CLK,
+	.ops	= &k210_bypass_ops,
+};

include/kendryte/bypass.h

@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2020 Sean Anderson <seanga2@gmail.com>
+ */
+#ifndef K210_BYPASS_H
+#define K210_BYPASS_H
+
+#include <clk.h>
+
+struct k210_bypass {
+	struct clk clk;
+	struct clk **children; /* Clocks to reparent */
+	struct clk **saved_parents; /* Parents saved over en-/dis-able */
+	struct clk *bypassee; /* Clock to bypass */
+	const struct clk_ops *bypassee_ops; /* Ops of the bypass clock */
+	struct clk *alt; /* Clock to set children to when bypassing */
+	size_t child_count;
+};
+
+#define to_k210_bypass(_clk) container_of(_clk, struct k210_bypass, clk)
+
+int k210_bypass_set_children(struct clk *clk, struct clk **children,
+			     size_t child_count);
+struct clk *k210_register_bypass_struct(const char *name,
+					const char *parent_name,
+					struct k210_bypass *bypass);
+struct clk *k210_register_bypass(const char *name, const char *parent_name,
+				 struct clk *bypassee,
+				 const struct clk_ops *bypassee_ops,
+				 struct clk *alt);
+#endif /* K210_BYPASS_H */