clk-apple-nco.c
// 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");