diff options
Diffstat (limited to 'drivers/clk/clk-apple-nco.c')
| -rw-r--r-- | drivers/clk/clk-apple-nco.c | 334 |
1 files changed, 334 insertions, 0 deletions
diff --git a/drivers/clk/clk-apple-nco.c b/drivers/clk/clk-apple-nco.c new file mode 100644 index 000000000000..39472a51530a --- /dev/null +++ b/drivers/clk/clk-apple-nco.c @@ -0,0 +1,334 @@ +// SPDX-License-Identifier: GPL-2.0-only OR MIT +/* + * Driver for an SoC block (Numerically Controlled Oscillator) + * found on t8103 (M1) and other Apple chips + * + * Copyright (C) The Asahi Linux Contributors + */ + +#include <linux/bits.h> +#include <linux/bitfield.h> +#include <linux/clk-provider.h> +#include <linux/io.h> +#include <linux/kernel.h> +#include <linux/math64.h> +#include <linux/module.h> +#include <linux/of.h> +#include <linux/platform_device.h> +#include <linux/spinlock.h> + +#define NCO_CHANNEL_STRIDE 0x4000 +#define NCO_CHANNEL_REGSIZE 20 + +#define REG_CTRL 0 +#define CTRL_ENABLE BIT(31) +#define REG_DIV 4 +#define DIV_FINE GENMASK(1, 0) +#define DIV_COARSE GENMASK(12, 2) +#define REG_INC1 8 +#define REG_INC2 12 +#define REG_ACCINIT 16 + +/* + * Theory of operation (postulated) + * + * The REG_DIV register indirectly expresses a base integer divisor, roughly + * corresponding to twice the desired ratio of input to output clock. This + * base divisor is adjusted on a cycle-by-cycle basis based on the state of a + * 32-bit phase accumulator to achieve a desired precise clock ratio over the + * long term. + * + * Specifically an output clock cycle is produced after (REG_DIV divisor)/2 + * or (REG_DIV divisor + 1)/2 input cycles, the latter taking effect when top + * bit of the 32-bit accumulator is set. The accumulator is incremented each + * produced output cycle, by the value from either REG_INC1 or REG_INC2, which + * of the two is selected depending again on the accumulator's current top bit. + * + * Because the NCO hardware implements counting of input clock cycles in part + * in a Galois linear-feedback shift register, the higher bits of divisor + * are programmed into REG_DIV by picking an appropriate LFSR state. See + * applnco_compute_tables/applnco_div_translate for details on this. + */ + +#define LFSR_POLY 0xa01 +#define LFSR_INIT 0x7ff +#define LFSR_LEN 11 +#define LFSR_PERIOD ((1 << LFSR_LEN) - 1) +#define LFSR_TBLSIZE (1 << LFSR_LEN) + +/* The minimal attainable coarse divisor (first value in table) */ +#define COARSE_DIV_OFFSET 2 + +struct applnco_tables { + u16 fwd[LFSR_TBLSIZE]; + u16 inv[LFSR_TBLSIZE]; +}; + +struct applnco_channel { + void __iomem *base; + struct applnco_tables *tbl; + struct clk_hw hw; + + spinlock_t lock; +}; + +#define to_applnco_channel(_hw) container_of(_hw, struct applnco_channel, hw) + +static void applnco_enable_nolock(struct clk_hw *hw) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + u32 val; + + val = readl_relaxed(chan->base + REG_CTRL); + writel_relaxed(val | CTRL_ENABLE, chan->base + REG_CTRL); +} + +static void applnco_disable_nolock(struct clk_hw *hw) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + u32 val; + + val = readl_relaxed(chan->base + REG_CTRL); + writel_relaxed(val & ~CTRL_ENABLE, chan->base + REG_CTRL); +} + +static int applnco_is_enabled(struct clk_hw *hw) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + + return (readl_relaxed(chan->base + REG_CTRL) & CTRL_ENABLE) != 0; +} + +static void applnco_compute_tables(struct applnco_tables *tbl) +{ + int i; + u32 state = LFSR_INIT; + + /* + * Go through the states of a Galois LFSR and build + * a coarse divisor translation table. + */ + for (i = LFSR_PERIOD; i > 0; i--) { + if (state & 1) + state = (state >> 1) ^ (LFSR_POLY >> 1); + else + state = (state >> 1); + tbl->fwd[i] = state; + tbl->inv[state] = i; + } + + /* Zero value is special-cased */ + tbl->fwd[0] = 0; + tbl->inv[0] = 0; +} + +static bool applnco_div_out_of_range(unsigned int div) +{ + unsigned int coarse = div / 4; + + return coarse < COARSE_DIV_OFFSET || + coarse >= COARSE_DIV_OFFSET + LFSR_TBLSIZE; +} + +static u32 applnco_div_translate(struct applnco_tables *tbl, unsigned int div) +{ + unsigned int coarse = div / 4; + + if (WARN_ON(applnco_div_out_of_range(div))) + return 0; + + return FIELD_PREP(DIV_COARSE, tbl->fwd[coarse - COARSE_DIV_OFFSET]) | + FIELD_PREP(DIV_FINE, div % 4); +} + +static unsigned int applnco_div_translate_inv(struct applnco_tables *tbl, u32 regval) +{ + unsigned int coarse, fine; + + coarse = tbl->inv[FIELD_GET(DIV_COARSE, regval)] + COARSE_DIV_OFFSET; + fine = FIELD_GET(DIV_FINE, regval); + + return coarse * 4 + fine; +} + +static int applnco_set_rate(struct clk_hw *hw, unsigned long rate, + unsigned long parent_rate) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + unsigned long flags; + u32 div, inc1, inc2; + bool was_enabled; + + div = 2 * parent_rate / rate; + inc1 = 2 * parent_rate - div * rate; + inc2 = inc1 - rate; + + if (applnco_div_out_of_range(div)) + return -EINVAL; + + div = applnco_div_translate(chan->tbl, div); + + spin_lock_irqsave(&chan->lock, flags); + was_enabled = applnco_is_enabled(hw); + applnco_disable_nolock(hw); + + writel_relaxed(div, chan->base + REG_DIV); + writel_relaxed(inc1, chan->base + REG_INC1); + writel_relaxed(inc2, chan->base + REG_INC2); + + /* Presumably a neutral initial value for accumulator */ + writel_relaxed(1 << 31, chan->base + REG_ACCINIT); + + if (was_enabled) + applnco_enable_nolock(hw); + spin_unlock_irqrestore(&chan->lock, flags); + + return 0; +} + +static unsigned long applnco_recalc_rate(struct clk_hw *hw, + unsigned long parent_rate) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + u32 div, inc1, inc2, incbase; + + div = applnco_div_translate_inv(chan->tbl, + readl_relaxed(chan->base + REG_DIV)); + + inc1 = readl_relaxed(chan->base + REG_INC1); + inc2 = readl_relaxed(chan->base + REG_INC2); + + /* + * We don't support wraparound of accumulator + * nor the edge case of both increments being zero + */ + if (inc1 >= (1 << 31) || inc2 < (1 << 31) || (inc1 == 0 && inc2 == 0)) + return 0; + + /* Scale both sides of division by incbase to maintain precision */ + incbase = inc1 - inc2; + + return div64_u64(((u64) parent_rate) * 2 * incbase, + ((u64) div) * incbase + inc1); +} + +static long applnco_round_rate(struct clk_hw *hw, unsigned long rate, + unsigned long *parent_rate) +{ + unsigned long lo = *parent_rate / (COARSE_DIV_OFFSET + LFSR_TBLSIZE) + 1; + unsigned long hi = *parent_rate / COARSE_DIV_OFFSET; + + return clamp(rate, lo, hi); +} + +static int applnco_enable(struct clk_hw *hw) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + unsigned long flags; + + spin_lock_irqsave(&chan->lock, flags); + applnco_enable_nolock(hw); + spin_unlock_irqrestore(&chan->lock, flags); + + return 0; +} + +static void applnco_disable(struct clk_hw *hw) +{ + struct applnco_channel *chan = to_applnco_channel(hw); + unsigned long flags; + + spin_lock_irqsave(&chan->lock, flags); + applnco_disable_nolock(hw); + spin_unlock_irqrestore(&chan->lock, flags); +} + +static const struct clk_ops applnco_ops = { + .set_rate = applnco_set_rate, + .recalc_rate = applnco_recalc_rate, + .round_rate = applnco_round_rate, + .enable = applnco_enable, + .disable = applnco_disable, + .is_enabled = applnco_is_enabled, +}; + +static int applnco_probe(struct platform_device *pdev) +{ + struct device_node *np = pdev->dev.of_node; + struct clk_parent_data pdata = { .index = 0 }; + struct clk_init_data init; + struct clk_hw_onecell_data *onecell_data; + void __iomem *base; + struct resource *res; + struct applnco_tables *tbl; + unsigned int nchannels; + int ret, i; + + base = devm_platform_get_and_ioremap_resource(pdev, 0, &res); + if (IS_ERR(base)) + return PTR_ERR(base); + + if (resource_size(res) < NCO_CHANNEL_REGSIZE) + return -EINVAL; + nchannels = (resource_size(res) - NCO_CHANNEL_REGSIZE) + / NCO_CHANNEL_STRIDE + 1; + + onecell_data = devm_kzalloc(&pdev->dev, struct_size(onecell_data, hws, + nchannels), GFP_KERNEL); + if (!onecell_data) + return -ENOMEM; + onecell_data->num = nchannels; + + tbl = devm_kzalloc(&pdev->dev, sizeof(*tbl), GFP_KERNEL); + if (!tbl) + return -ENOMEM; + applnco_compute_tables(tbl); + + for (i = 0; i < nchannels; i++) { + struct applnco_channel *chan; + + chan = devm_kzalloc(&pdev->dev, sizeof(*chan), GFP_KERNEL); + if (!chan) + return -ENOMEM; + chan->base = base + NCO_CHANNEL_STRIDE * i; + chan->tbl = tbl; + spin_lock_init(&chan->lock); + + memset(&init, 0, sizeof(init)); + init.name = devm_kasprintf(&pdev->dev, GFP_KERNEL, + "%s-%d", np->name, i); + init.ops = &applnco_ops; + init.parent_data = &pdata; + init.num_parents = 1; + init.flags = 0; + + chan->hw.init = &init; + ret = devm_clk_hw_register(&pdev->dev, &chan->hw); + if (ret) + return ret; + + onecell_data->hws[i] = &chan->hw; + } + + return devm_of_clk_add_hw_provider(&pdev->dev, of_clk_hw_onecell_get, + onecell_data); +} + +static const struct of_device_id applnco_ids[] = { + { .compatible = "apple,nco" }, + { } +}; +MODULE_DEVICE_TABLE(of, applnco_ids); + +static struct platform_driver applnco_driver = { + .driver = { + .name = "apple-nco", + .of_match_table = applnco_ids, + }, + .probe = applnco_probe, +}; +module_platform_driver(applnco_driver); + +MODULE_AUTHOR("Martin PoviĊĦer <povik+lin@cutebit.org>"); +MODULE_DESCRIPTION("Clock driver for NCO blocks on Apple SoCs"); +MODULE_LICENSE("GPL"); |