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clk: stm32f4: support spread spectrum clock generation
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Support spread spectrum clock generation for the main PLL, the only one
for which this functionality is available.

Tested on the STM32F469I-DISCO board.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

Link: https://lore.kernel.org/r/20250114182021.670435-5-dario.binacchi@amarulasolutions.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
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Dario Binacchi authored and Stephen Boyd committed Jan 15, 2025
1 parent a132837 commit 65b3516
Showing 1 changed file with 140 additions and 3 deletions.
143 changes: 140 additions & 3 deletions drivers/clk/clk-stm32f4.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -35,13 +35,20 @@
#define STM32F4_RCC_APB2ENR 0x44
#define STM32F4_RCC_BDCR 0x70
#define STM32F4_RCC_CSR 0x74
#define STM32F4_RCC_SSCGR 0x80
#define STM32F4_RCC_PLLI2SCFGR 0x84
#define STM32F4_RCC_PLLSAICFGR 0x88
#define STM32F4_RCC_DCKCFGR 0x8c
#define STM32F7_RCC_DCKCFGR2 0x90

#define STM32F4_RCC_PLLCFGR_N_MASK GENMASK(14, 6)

#define STM32F4_RCC_SSCGR_SSCGEN BIT(31)
#define STM32F4_RCC_SSCGR_SPREADSEL BIT(30)
#define STM32F4_RCC_SSCGR_RESERVED_MASK GENMASK(29, 28)
#define STM32F4_RCC_SSCGR_INCSTEP_MASK GENMASK(27, 13)
#define STM32F4_RCC_SSCGR_MODPER_MASK GENMASK(12, 0)

#define NONE -1
#define NO_IDX NONE
#define NO_MUX NONE
Expand Down Expand Up @@ -367,6 +374,16 @@ static const struct stm32f4_gate_data stm32f769_gates[] __initconst = {
{ STM32F4_RCC_APB2ENR, 30, "mdio", "apb2_div" },
};

enum stm32f4_pll_ssc_mod_type {
STM32F4_PLL_SSC_CENTER_SPREAD,
STM32F4_PLL_SSC_DOWN_SPREAD,
};

static const char * const stm32f4_ssc_mod_methods[] __initconst = {
[STM32F4_PLL_SSC_DOWN_SPREAD] = "down-spread",
[STM32F4_PLL_SSC_CENTER_SPREAD] = "center-spread",
};

/*
* This bitmask tells us which bit offsets (0..192) on STM32F4[23]xxx
* have gate bits associated with them. Its combined hweight is 71.
Expand Down Expand Up @@ -512,13 +529,21 @@ static const struct clk_div_table pll_divr_table[] = {
{ 2, 2 }, { 3, 3 }, { 4, 4 }, { 5, 5 }, { 6, 6 }, { 7, 7 }, { 0 }
};

struct stm32f4_pll_ssc {
unsigned int mod_freq;
unsigned int mod_depth;
enum stm32f4_pll_ssc_mod_type mod_type;
};

struct stm32f4_pll {
spinlock_t *lock;
struct clk_gate gate;
u8 offset;
u8 bit_rdy_idx;
u8 status;
u8 n_start;
bool ssc_enable;
struct stm32f4_pll_ssc ssc_conf;
};

#define to_stm32f4_pll(_gate) container_of(_gate, struct stm32f4_pll, gate)
Expand All @@ -541,6 +566,7 @@ struct stm32f4_vco_data {
u8 offset;
u8 bit_idx;
u8 bit_rdy_idx;
bool sscg;
};

static const struct stm32f4_vco_data vco_data[] = {
Expand Down Expand Up @@ -661,6 +687,32 @@ static long stm32f4_pll_round_rate(struct clk_hw *hw, unsigned long rate,
return *prate * n;
}

static void stm32f4_pll_set_ssc(struct clk_hw *hw, unsigned long parent_rate,
unsigned int ndiv)
{
struct clk_gate *gate = to_clk_gate(hw);
struct stm32f4_pll *pll = to_stm32f4_pll(gate);
struct stm32f4_pll_ssc *ssc = &pll->ssc_conf;
u32 modeper, incstep;
u32 sscgr;

sscgr = readl(base + STM32F4_RCC_SSCGR);
/* reserved field must be kept at reset value */
sscgr &= STM32F4_RCC_SSCGR_RESERVED_MASK;

modeper = DIV_ROUND_CLOSEST(parent_rate, 4 * ssc->mod_freq);
incstep = DIV_ROUND_CLOSEST(((1 << 15) - 1) * ssc->mod_depth * ndiv,
5 * 10000 * modeper);
sscgr |= STM32F4_RCC_SSCGR_SSCGEN |
FIELD_PREP(STM32F4_RCC_SSCGR_INCSTEP_MASK, incstep) |
FIELD_PREP(STM32F4_RCC_SSCGR_MODPER_MASK, modeper);

if (ssc->mod_type)
sscgr |= STM32F4_RCC_SSCGR_SPREADSEL;

writel(sscgr, base + STM32F4_RCC_SSCGR);
}

static int stm32f4_pll_set_rate(struct clk_hw *hw, unsigned long rate,
unsigned long parent_rate)
{
Expand All @@ -683,6 +735,9 @@ static int stm32f4_pll_set_rate(struct clk_hw *hw, unsigned long rate,

writel(val, base + pll->offset);

if (pll->ssc_enable)
stm32f4_pll_set_ssc(hw, parent_rate, n);

if (pll_state)
stm32f4_pll_enable(hw);

Expand Down Expand Up @@ -788,6 +843,84 @@ static struct clk_hw *clk_register_pll_div(const char *name,
return hw;
}

static int __init stm32f4_pll_init_ssc(struct clk_hw *hw,
const struct stm32f4_pll_ssc *conf)
{
struct clk_gate *gate = to_clk_gate(hw);
struct stm32f4_pll *pll = to_stm32f4_pll(gate);
struct clk_hw *parent;
unsigned long parent_rate;
int pll_state;
unsigned long n, val;

parent = clk_hw_get_parent(hw);
if (!parent) {
pr_err("%s: failed to get clock parent\n", __func__);
return -ENODEV;
}

parent_rate = clk_hw_get_rate(parent);

pll->ssc_enable = true;
memcpy(&pll->ssc_conf, conf, sizeof(pll->ssc_conf));

pll_state = stm32f4_pll_is_enabled(hw);

if (pll_state)
stm32f4_pll_disable(hw);

val = readl(base + pll->offset);
n = FIELD_GET(STM32F4_RCC_PLLCFGR_N_MASK, val);

pr_debug("%s: pll: %s, parent: %s, parent-rate: %lu, n: %lu\n",
__func__, clk_hw_get_name(hw), clk_hw_get_name(parent),
parent_rate, n);

stm32f4_pll_set_ssc(hw, parent_rate, n);

if (pll_state)
stm32f4_pll_enable(hw);

return 0;
}

static int __init stm32f4_pll_ssc_parse_dt(struct device_node *np,
struct stm32f4_pll_ssc *conf)
{
int ret;
const char *s;

if (!conf)
return -EINVAL;

ret = of_property_read_u32(np, "st,ssc-modfreq-hz", &conf->mod_freq);
if (ret)
return ret;

ret = of_property_read_u32(np, "st,ssc-moddepth-permyriad",
&conf->mod_depth);
if (ret) {
pr_err("%pOF: missing st,ssc-moddepth-permyriad\n", np);
return ret;
}

ret = fwnode_property_match_property_string(of_fwnode_handle(np),
"st,ssc-modmethod",
stm32f4_ssc_mod_methods,
ARRAY_SIZE(stm32f4_ssc_mod_methods));
if (ret < 0) {
pr_err("%pOF: failed to get st,ssc-modmethod\n", np);
return ret;
}

conf->mod_type = ret;

pr_debug("%pOF: SSCG settings: mod_freq: %d, mod_depth: %d mod_method: %s [%d]\n",
np, conf->mod_freq, conf->mod_depth, s, conf->mod_type);

return 0;
}

static struct clk_hw *stm32f4_rcc_register_pll(const char *pllsrc,
const struct stm32f4_pll_data *data, spinlock_t *lock)
{
Expand Down Expand Up @@ -1695,7 +1828,8 @@ static void __init stm32f4_rcc_init(struct device_node *np)
const struct of_device_id *match;
const struct stm32f4_clk_data *data;
unsigned long pllm;
struct clk_hw *pll_src_hw;
struct clk_hw *pll_src_hw, *pll_vco_hw;
struct stm32f4_pll_ssc ssc_conf;

base = of_iomap(np, 0);
if (!base) {
Expand Down Expand Up @@ -1754,8 +1888,8 @@ static void __init stm32f4_rcc_init(struct device_node *np)
clk_hw_register_fixed_factor(NULL, "vco_in", pll_src,
0, 1, pllm);

stm32f4_rcc_register_pll("vco_in", &data->pll_data[0],
&stm32f4_clk_lock);
pll_vco_hw = stm32f4_rcc_register_pll("vco_in", &data->pll_data[0],
&stm32f4_clk_lock);

clks[PLL_VCO_I2S] = stm32f4_rcc_register_pll("vco_in",
&data->pll_data[1], &stm32f4_clk_lock);
Expand Down Expand Up @@ -1900,6 +2034,9 @@ static void __init stm32f4_rcc_init(struct device_node *np)

of_clk_add_hw_provider(np, stm32f4_rcc_lookup_clk, NULL);

if (!stm32f4_pll_ssc_parse_dt(np, &ssc_conf))
stm32f4_pll_init_ssc(pll_vco_hw, &ssc_conf);

return;
fail:
kfree(clks);
Expand Down

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