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-rw-r--r--drivers/clk/clk-fractional-divider.c312
1 files changed, 312 insertions, 0 deletions
diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
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index 0000000000..479297763e
--- /dev/null
+++ b/drivers/clk/clk-fractional-divider.c
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+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2014 Intel Corporation
+ *
+ * Adjustable fractional divider clock implementation.
+ * Uses rational best approximation algorithm.
+ *
+ * Output is calculated as
+ *
+ * rate = (m / n) * parent_rate (1)
+ *
+ * This is useful when we have a prescaler block which asks for
+ * m (numerator) and n (denominator) values to be provided to satisfy
+ * the (1) as much as possible.
+ *
+ * Since m and n have the limitation by a range, e.g.
+ *
+ * n >= 1, n < N_width, where N_width = 2^nwidth (2)
+ *
+ * for some cases the output may be saturated. Hence, from (1) and (2),
+ * assuming the worst case when m = 1, the inequality
+ *
+ * floor(log2(parent_rate / rate)) <= nwidth (3)
+ *
+ * may be derived. Thus, in cases when
+ *
+ * (parent_rate / rate) >> N_width (4)
+ *
+ * we might scale up the rate by 2^scale (see the description of
+ * CLK_FRAC_DIVIDER_POWER_OF_TWO_PS for additional information), where
+ *
+ * scale = floor(log2(parent_rate / rate)) - nwidth (5)
+ *
+ * and assume that the IP, that needs m and n, has also its own
+ * prescaler, which is capable to divide by 2^scale. In this way
+ * we get the denominator to satisfy the desired range (2) and
+ * at the same time a much better result of m and n than simple
+ * saturated values.
+ */
+
+#include <linux/debugfs.h>
+#include <linux/device.h>
+#include <linux/io.h>
+#include <linux/math.h>
+#include <linux/module.h>
+#include <linux/rational.h>
+#include <linux/slab.h>
+
+#include <linux/clk-provider.h>
+
+#include "clk-fractional-divider.h"
+
+static inline u32 clk_fd_readl(struct clk_fractional_divider *fd)
+{
+ if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN)
+ return ioread32be(fd->reg);
+
+ return readl(fd->reg);
+}
+
+static inline void clk_fd_writel(struct clk_fractional_divider *fd, u32 val)
+{
+ if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN)
+ iowrite32be(val, fd->reg);
+ else
+ writel(val, fd->reg);
+}
+
+static void clk_fd_get_div(struct clk_hw *hw, struct u32_fract *fract)
+{
+ struct clk_fractional_divider *fd = to_clk_fd(hw);
+ unsigned long flags = 0;
+ unsigned long m, n;
+ u32 mmask, nmask;
+ u32 val;
+
+ if (fd->lock)
+ spin_lock_irqsave(fd->lock, flags);
+ else
+ __acquire(fd->lock);
+
+ val = clk_fd_readl(fd);
+
+ if (fd->lock)
+ spin_unlock_irqrestore(fd->lock, flags);
+ else
+ __release(fd->lock);
+
+ mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
+ nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
+
+ m = (val & mmask) >> fd->mshift;
+ n = (val & nmask) >> fd->nshift;
+
+ if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+ m++;
+ n++;
+ }
+
+ fract->numerator = m;
+ fract->denominator = n;
+}
+
+static unsigned long clk_fd_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
+{
+ struct u32_fract fract;
+ u64 ret;
+
+ clk_fd_get_div(hw, &fract);
+
+ if (!fract.numerator || !fract.denominator)
+ return parent_rate;
+
+ ret = (u64)parent_rate * fract.numerator;
+ do_div(ret, fract.denominator);
+
+ return ret;
+}
+
+void clk_fractional_divider_general_approximation(struct clk_hw *hw,
+ unsigned long rate,
+ unsigned long *parent_rate,
+ unsigned long *m, unsigned long *n)
+{
+ struct clk_fractional_divider *fd = to_clk_fd(hw);
+
+ /*
+ * Get rate closer to *parent_rate to guarantee there is no overflow
+ * for m and n. In the result it will be the nearest rate left shifted
+ * by (scale - fd->nwidth) bits.
+ *
+ * For the detailed explanation see the top comment in this file.
+ */
+ if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) {
+ unsigned long scale = fls_long(*parent_rate / rate - 1);
+
+ if (scale > fd->nwidth)
+ rate <<= scale - fd->nwidth;
+ }
+
+ rational_best_approximation(rate, *parent_rate,
+ GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
+ m, n);
+}
+
+static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
+ unsigned long *parent_rate)
+{
+ struct clk_fractional_divider *fd = to_clk_fd(hw);
+ unsigned long m, n;
+ u64 ret;
+
+ if (!rate || (!clk_hw_can_set_rate_parent(hw) && rate >= *parent_rate))
+ return *parent_rate;
+
+ if (fd->approximation)
+ fd->approximation(hw, rate, parent_rate, &m, &n);
+ else
+ clk_fractional_divider_general_approximation(hw, rate, parent_rate, &m, &n);
+
+ ret = (u64)*parent_rate * m;
+ do_div(ret, n);
+
+ return ret;
+}
+
+static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
+ unsigned long parent_rate)
+{
+ struct clk_fractional_divider *fd = to_clk_fd(hw);
+ unsigned long flags = 0;
+ unsigned long m, n;
+ u32 mmask, nmask;
+ u32 val;
+
+ rational_best_approximation(rate, parent_rate,
+ GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
+ &m, &n);
+
+ if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
+ m--;
+ n--;
+ }
+
+ if (fd->lock)
+ spin_lock_irqsave(fd->lock, flags);
+ else
+ __acquire(fd->lock);
+
+ mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
+ nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
+
+ val = clk_fd_readl(fd);
+ val &= ~(mmask | nmask);
+ val |= (m << fd->mshift) | (n << fd->nshift);
+ clk_fd_writel(fd, val);
+
+ if (fd->lock)
+ spin_unlock_irqrestore(fd->lock, flags);
+ else
+ __release(fd->lock);
+
+ return 0;
+}
+
+#ifdef CONFIG_DEBUG_FS
+static int clk_fd_numerator_get(void *hw, u64 *val)
+{
+ struct u32_fract fract;
+
+ clk_fd_get_div(hw, &fract);
+
+ *val = fract.numerator;
+
+ return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_numerator_fops, clk_fd_numerator_get, NULL, "%llu\n");
+
+static int clk_fd_denominator_get(void *hw, u64 *val)
+{
+ struct u32_fract fract;
+
+ clk_fd_get_div(hw, &fract);
+
+ *val = fract.denominator;
+
+ return 0;
+}
+DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_denominator_fops, clk_fd_denominator_get, NULL, "%llu\n");
+
+static void clk_fd_debug_init(struct clk_hw *hw, struct dentry *dentry)
+{
+ debugfs_create_file("numerator", 0444, dentry, hw, &clk_fd_numerator_fops);
+ debugfs_create_file("denominator", 0444, dentry, hw, &clk_fd_denominator_fops);
+}
+#endif
+
+const struct clk_ops clk_fractional_divider_ops = {
+ .recalc_rate = clk_fd_recalc_rate,
+ .round_rate = clk_fd_round_rate,
+ .set_rate = clk_fd_set_rate,
+#ifdef CONFIG_DEBUG_FS
+ .debug_init = clk_fd_debug_init,
+#endif
+};
+EXPORT_SYMBOL_GPL(clk_fractional_divider_ops);
+
+struct clk_hw *clk_hw_register_fractional_divider(struct device *dev,
+ const char *name, const char *parent_name, unsigned long flags,
+ void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
+ u8 clk_divider_flags, spinlock_t *lock)
+{
+ struct clk_fractional_divider *fd;
+ struct clk_init_data init;
+ struct clk_hw *hw;
+ int ret;
+
+ fd = kzalloc(sizeof(*fd), GFP_KERNEL);
+ if (!fd)
+ return ERR_PTR(-ENOMEM);
+
+ init.name = name;
+ init.ops = &clk_fractional_divider_ops;
+ init.flags = flags;
+ init.parent_names = parent_name ? &parent_name : NULL;
+ init.num_parents = parent_name ? 1 : 0;
+
+ fd->reg = reg;
+ fd->mshift = mshift;
+ fd->mwidth = mwidth;
+ fd->nshift = nshift;
+ fd->nwidth = nwidth;
+ fd->flags = clk_divider_flags;
+ fd->lock = lock;
+ fd->hw.init = &init;
+
+ hw = &fd->hw;
+ ret = clk_hw_register(dev, hw);
+ if (ret) {
+ kfree(fd);
+ hw = ERR_PTR(ret);
+ }
+
+ return hw;
+}
+EXPORT_SYMBOL_GPL(clk_hw_register_fractional_divider);
+
+struct clk *clk_register_fractional_divider(struct device *dev,
+ const char *name, const char *parent_name, unsigned long flags,
+ void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
+ u8 clk_divider_flags, spinlock_t *lock)
+{
+ struct clk_hw *hw;
+
+ hw = clk_hw_register_fractional_divider(dev, name, parent_name, flags,
+ reg, mshift, mwidth, nshift, nwidth, clk_divider_flags,
+ lock);
+ if (IS_ERR(hw))
+ return ERR_CAST(hw);
+ return hw->clk;
+}
+EXPORT_SYMBOL_GPL(clk_register_fractional_divider);
+
+void clk_hw_unregister_fractional_divider(struct clk_hw *hw)
+{
+ struct clk_fractional_divider *fd;
+
+ fd = to_clk_fd(hw);
+
+ clk_hw_unregister(hw);
+ kfree(fd);
+}