Re: [PATCH v5 5/5] clk: ti: add am33xx/am43xx spread spectrum clock support
From: Tero Kristo
Date: Mon Apr 19 2021 - 07:26:31 EST
On 18/04/2021 17:56, Dario Binacchi wrote:
The patch enables spread spectrum clocking (SSC) for MPU and LCD PLLs.
As reported by the TI spruh73x/spruhl7x RM, SSC is only supported for
the DISP/LCD and MPU PLLs on am33xx/am43xx. SSC is not supported for
DDR, PER, and CORE PLLs.
Calculating the required values and setting the registers accordingly
was taken from the set_mpu_spreadspectrum routine contained in the
arch/arm/mach-omap2/am33xx/clock_am33xx.c file of the u-boot project.
In locked condition, DPLL output clock = CLKINP *[M/N]. In case of
SSC enabled, the reference manual explains that there is a restriction
of range of M values. Since the omap2_dpll_round_rate routine attempts
to select the minimum possible N, the value of M obtained is not
guaranteed to be within the range required. With the new "ti,min-div"
parameter it is possible to increase N and consequently M to satisfy the
constraint imposed by SSC.
Signed-off-by: Dario Binacchi <dariobin@xxxxxxxxx>
Reviewed-by: Tero Kristo <kristo@xxxxxxxxxx>
---
Changes in v5:
- Remove ssc_ack_mask field from dpll_data structure. It was not used.
- Change ssc_downspread type from u8 to bool in dpll_data structure.
Changes in v4:
- Update commit message.
Changes in v3:
- Use "ti,ssc-modfreq-hz" binding instead of "ti,ssc-modfreq".
Changes in v2:
- Move the DT changes to the previous patch in the series.
drivers/clk/ti/dpll.c | 39 ++++++++++++++++++
drivers/clk/ti/dpll3xxx.c | 85 +++++++++++++++++++++++++++++++++++++++
include/linux/clk/ti.h | 22 ++++++++++
3 files changed, 146 insertions(+)
diff --git a/drivers/clk/ti/dpll.c b/drivers/clk/ti/dpll.c
index d6f1ac5b53e1..e9f9aee936ae 100644
--- a/drivers/clk/ti/dpll.c
+++ b/drivers/clk/ti/dpll.c
@@ -290,7 +290,9 @@ static void __init of_ti_dpll_setup(struct device_node *node,
struct clk_init_data *init = NULL;
const char **parent_names = NULL;
struct dpll_data *dd = NULL;
+ int ssc_clk_index;
u8 dpll_mode = 0;
+ u32 min_div;
dd = kmemdup(ddt, sizeof(*dd), GFP_KERNEL);
clk_hw = kzalloc(sizeof(*clk_hw), GFP_KERNEL);
@@ -345,6 +347,27 @@ static void __init of_ti_dpll_setup(struct device_node *node,
if (dd->autoidle_mask) {
if (ti_clk_get_reg_addr(node, 3, &dd->autoidle_reg))
goto cleanup;
+
+ ssc_clk_index = 4;
+ } else {
+ ssc_clk_index = 3;
+ }
+
+ if (dd->ssc_deltam_int_mask && dd->ssc_deltam_frac_mask &&
+ dd->ssc_modfreq_mant_mask && dd->ssc_modfreq_exp_mask) {
+ if (ti_clk_get_reg_addr(node, ssc_clk_index++,
+ &dd->ssc_deltam_reg))
+ goto cleanup;
+
+ if (ti_clk_get_reg_addr(node, ssc_clk_index++,
+ &dd->ssc_modfreq_reg))
+ goto cleanup;
+
+ of_property_read_u32(node, "ti,ssc-modfreq-hz",
+ &dd->ssc_modfreq);
+ of_property_read_u32(node, "ti,ssc-deltam", &dd->ssc_deltam);
+ dd->ssc_downspread =
+ of_property_read_bool(node, "ti,ssc-downspread");
}
if (of_property_read_bool(node, "ti,low-power-stop"))
@@ -356,6 +379,10 @@ static void __init of_ti_dpll_setup(struct device_node *node,
if (of_property_read_bool(node, "ti,lock"))
dpll_mode |= 1 << DPLL_LOCKED;
+ if (!of_property_read_u32(node, "ti,min-div", &min_div) &&
+ min_div > dd->min_divider)
+ dd->min_divider = min_div;
+
if (dpll_mode)
dd->modes = dpll_mode;
@@ -585,8 +612,14 @@ static void __init of_ti_am3_no_gate_dpll_setup(struct device_node *node)
const struct dpll_data dd = {
.idlest_mask = 0x1,
.enable_mask = 0x7,
+ .ssc_enable_mask = 0x1 << 12,
+ .ssc_downspread_mask = 0x1 << 14,
.mult_mask = 0x7ff << 8,
.div1_mask = 0x7f,
+ .ssc_deltam_int_mask = 0x3 << 18,
+ .ssc_deltam_frac_mask = 0x3ffff,
+ .ssc_modfreq_mant_mask = 0x7f,
+ .ssc_modfreq_exp_mask = 0x7 << 8,
.max_multiplier = 2047,
.max_divider = 128,
.min_divider = 1,
@@ -645,8 +678,14 @@ static void __init of_ti_am3_dpll_setup(struct device_node *node)
const struct dpll_data dd = {
.idlest_mask = 0x1,
.enable_mask = 0x7,
+ .ssc_enable_mask = 0x1 << 12,
+ .ssc_downspread_mask = 0x1 << 14,
.mult_mask = 0x7ff << 8,
.div1_mask = 0x7f,
+ .ssc_deltam_int_mask = 0x3 << 18,
+ .ssc_deltam_frac_mask = 0x3ffff,
+ .ssc_modfreq_mant_mask = 0x7f,
+ .ssc_modfreq_exp_mask = 0x7 << 8,
.max_multiplier = 2047,
.max_divider = 128,
.min_divider = 1,
diff --git a/drivers/clk/ti/dpll3xxx.c b/drivers/clk/ti/dpll3xxx.c
index 94d5b5fe9a2b..e32b3515f9e7 100644
--- a/drivers/clk/ti/dpll3xxx.c
+++ b/drivers/clk/ti/dpll3xxx.c
@@ -291,6 +291,88 @@ static void _lookup_sddiv(struct clk_hw_omap *clk, u8 *sd_div, u16 m, u8 n)
*sd_div = sd;
}
+/**
+ * omap3_noncore_dpll_ssc_program - set spread-spectrum clocking registers
+ * @clk: struct clk * of DPLL to set
+ *
+ * Enable the DPLL spread spectrum clocking if frequency modulation and
+ * frequency spreading have been set, otherwise disable it.
+ */
+static void omap3_noncore_dpll_ssc_program(struct clk_hw_omap *clk)
+{
+ struct dpll_data *dd = clk->dpll_data;
+ unsigned long ref_rate;
+ u32 v, ctrl, mod_freq_divider, exponent, mantissa;
+ u32 deltam_step, deltam_ceil;
+
+ ctrl = ti_clk_ll_ops->clk_readl(&dd->control_reg);
+
+ if (dd->ssc_modfreq && dd->ssc_deltam) {
+ ctrl |= dd->ssc_enable_mask;
+
+ if (dd->ssc_downspread)
+ ctrl |= dd->ssc_downspread_mask;
+ else
+ ctrl &= ~dd->ssc_downspread_mask;
+
+ ref_rate = clk_hw_get_rate(dd->clk_ref);
+ mod_freq_divider =
+ (ref_rate / dd->last_rounded_n) / (4 * dd->ssc_modfreq);
+ if (dd->ssc_modfreq > (ref_rate / 70))
+ pr_warn("clock: SSC modulation frequency of DPLL %s greater than %ld\n",
+ __clk_get_name(clk->hw.clk), ref_rate / 70);
+
+ exponent = 0;
+ mantissa = mod_freq_divider;
+ while ((mantissa > 127) && (exponent < 7)) {
+ exponent++;
+ mantissa /= 2;
+ }
+ if (mantissa > 127)
+ mantissa = 127;
+
+ v = ti_clk_ll_ops->clk_readl(&dd->ssc_modfreq_reg);
+ v &= ~(dd->ssc_modfreq_mant_mask | dd->ssc_modfreq_exp_mask);
+ v |= mantissa << __ffs(dd->ssc_modfreq_mant_mask);
+ v |= exponent << __ffs(dd->ssc_modfreq_exp_mask);
+ ti_clk_ll_ops->clk_writel(v, &dd->ssc_modfreq_reg);
+
+ deltam_step = dd->last_rounded_m * dd->ssc_deltam;
+ deltam_step /= 10;
+ if (dd->ssc_downspread)
+ deltam_step /= 2;
+
+ deltam_step <<= __ffs(dd->ssc_deltam_int_mask);
+ deltam_step /= 100;
+ deltam_step /= mod_freq_divider;
+ if (deltam_step > 0xFFFFF)
+ deltam_step = 0xFFFFF;
+
+ deltam_ceil = (deltam_step & dd->ssc_deltam_int_mask) >>
+ __ffs(dd->ssc_deltam_int_mask);
+ if (deltam_step & dd->ssc_deltam_frac_mask)
+ deltam_ceil++;
+
+ if ((dd->ssc_downspread &&
+ ((dd->last_rounded_m - (2 * deltam_ceil)) < 20 ||
+ dd->last_rounded_m > 2045)) ||
+ ((dd->last_rounded_m - deltam_ceil) < 20 ||
+ (dd->last_rounded_m + deltam_ceil) > 2045))
+ pr_warn("clock: SSC multiplier of DPLL %s is out of range\n",
+ __clk_get_name(clk->hw.clk));
+
+ v = ti_clk_ll_ops->clk_readl(&dd->ssc_deltam_reg);
+ v &= ~(dd->ssc_deltam_int_mask | dd->ssc_deltam_frac_mask);
+ v |= deltam_step << __ffs(dd->ssc_deltam_int_mask |
+ dd->ssc_deltam_frac_mask);
+ ti_clk_ll_ops->clk_writel(v, &dd->ssc_deltam_reg);
+ } else {
+ ctrl &= ~dd->ssc_enable_mask;
+ }
+
+ ti_clk_ll_ops->clk_writel(ctrl, &dd->control_reg);
+}
+
/**
* omap3_noncore_dpll_program - set non-core DPLL M,N values directly
* @clk: struct clk * of DPLL to set
@@ -390,6 +472,9 @@ static int omap3_noncore_dpll_program(struct clk_hw_omap *clk, u16 freqsel)
ti_clk_ll_ops->clk_writel(v, &dd->control_reg);
}
+ if (dd->ssc_enable_mask)
+ omap3_noncore_dpll_ssc_program(clk);
+
/* We let the clock framework set the other output dividers later */
/* REVISIT: Set ramp-up delay? */
diff --git a/include/linux/clk/ti.h b/include/linux/clk/ti.h
index c62f6fa6763d..3486f20a3753 100644
--- a/include/linux/clk/ti.h
+++ b/include/linux/clk/ti.h
@@ -63,6 +63,17 @@ struct clk_omap_reg {
* @auto_recal_bit: bitshift of the driftguard enable bit in @control_reg
* @recal_en_bit: bitshift of the PRM_IRQENABLE_* bit for recalibration IRQs
* @recal_st_bit: bitshift of the PRM_IRQSTATUS_* bit for recalibration IRQs
+ * @ssc_deltam_reg: register containing the DPLL SSC frequency spreading
+ * @ssc_modfreq_reg: register containing the DPLL SSC modulation frequency
+ * @ssc_modfreq_mant_mask: mask of the mantissa component in @ssc_modfreq_reg
+ * @ssc_modfreq_exp_mask: mask of the exponent component in @ssc_modfreq_reg
+ * @ssc_enable_mask: mask of the DPLL SSC enable bit in @control_reg
+ * @ssc_downspread_mask: mask of the DPLL SSC low frequency only bit in
+ * @control_reg
+ * @ssc_modfreq: the DPLL SSC frequency modulation in kHz
+ * @ssc_deltam: the DPLL SSC frequency spreading in permille (10th of percent)
+ * @ssc_downspread: require the only low frequency spread of the DPLL in SSC
+ * mode
* @flags: DPLL type/features (see below)
*
* Possible values for @flags:
@@ -110,6 +121,17 @@ struct dpll_data {
u8 auto_recal_bit;
u8 recal_en_bit;
u8 recal_st_bit;
+ struct clk_omap_reg ssc_deltam_reg;
+ struct clk_omap_reg ssc_modfreq_reg;
+ u32 ssc_deltam_int_mask;
+ u32 ssc_deltam_frac_mask;
+ u32 ssc_modfreq_mant_mask;
+ u32 ssc_modfreq_exp_mask;
+ u32 ssc_enable_mask;
+ u32 ssc_downspread_mask;
+ u32 ssc_modfreq;
+ u32 ssc_deltam;
+ bool ssc_downspread;
u8 flags;
};