clk: ti: add am33xx/am43xx spread spectrum clock support

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 clk_ti_am3_dpll_round_rate() 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.

Link: https://lore.kernel.org/r/20210606202253.31649-6-dariobin@libero.it
Signed-off-by: Dario Binacchi <dariobin@libero.it>

diff --git a/arch/arm/include/asm/arch-am33xx/clock.h b/arch/arm/include/asm/arch-am33xx/clock.h
index 5d775902bbe018495cebb5436fa3f773524ebf63..79e3b8c7d9f97501eb28f3d1f6cf9c6114b3db49 100644 (file)
--- a/arch/arm/include/asm/arch-am33xx/clock.h
+++ b/arch/arm/include/asm/arch-am33xx/clock.h
@@ -78,6 +78,18 @@
 #define CM_CLKSEL_DPLL_N_SHIFT                 0
 #define CM_CLKSEL_DPLL_N_MASK                  0x7F
 
+/* CM_SSC_DELTAM_DPLL */
+#define CM_SSC_DELTAM_DPLL_FRAC_SHIFT          0
+#define CM_SSC_DELTAM_DPLL_FRAC_MASK           GENMASK(17, 0)
+#define CM_SSC_DELTAM_DPLL_INT_SHIFT           18
+#define CM_SSC_DELTAM_DPLL_INT_MASK            GENMASK(19, 18)
+
+/* CM_SSC_MODFREQ_DPLL */
+#define CM_SSC_MODFREQ_DPLL_MANT_SHIFT         0
+#define CM_SSC_MODFREQ_DPLL_MANT_MASK          GENMASK(6, 0)
+#define CM_SSC_MODFREQ_DPLL_EXP_SHIFT          7
+#define CM_SSC_MODFREQ_DPLL_EXP_MASK           GENMASK(10, 8)
+
 struct dpll_params {
        u32 m;
        u32 n;

diff --git a/drivers/clk/ti/clk-am3-dpll.c b/drivers/clk/ti/clk-am3-dpll.c
index 916d3080340113b046614ae4ca1d803c09f3afb9..398a011a5cea9c82c2d38c823a2bc498c870e6c9 100644 (file)
--- a/drivers/clk/ti/clk-am3-dpll.c
+++ b/drivers/clk/ti/clk-am3-dpll.c
@@ -27,11 +27,17 @@ struct clk_ti_am3_dpll_priv {
        struct clk_ti_reg clkmode_reg;
        struct clk_ti_reg idlest_reg;
        struct clk_ti_reg clksel_reg;
+       struct clk_ti_reg ssc_deltam_reg;
+       struct clk_ti_reg ssc_modfreq_reg;
        struct clk clk_bypass;
        struct clk clk_ref;
        u16 last_rounded_mult;
        u8 last_rounded_div;
+       u8 min_div;
        ulong max_rate;
+       u32 ssc_modfreq;
+       u32 ssc_deltam;
+       bool ssc_downspread;
 };
 
 static ulong clk_ti_am3_dpll_round_rate(struct clk *clk, ulong rate)
@@ -51,7 +57,7 @@ static ulong clk_ti_am3_dpll_round_rate(struct clk *clk, ulong rate)
        err = rate;
        err_min = rate;
        ref_rate = clk_get_rate(&priv->clk_ref);
-       for (d = 1; err_min && d <= 128; d++) {
+       for (d = priv->min_div; err_min && d <= 128; d++) {
                for (m = 2; m <= 2047; m++) {
                        r = (ref_rate * m) / d;
                        err = abs(r - rate);
@@ -71,8 +77,8 @@ static ulong clk_ti_am3_dpll_round_rate(struct clk *clk, ulong rate)
 
        priv->last_rounded_mult = mult;
        priv->last_rounded_div = div;
-       dev_dbg(clk->dev, "rate=%ld, best_rate=%ld, mult=%d, div=%d\n", rate,
-               ret, mult, div);
+       dev_dbg(clk->dev, "rate=%ld, min-div: %d, best_rate=%ld, mult=%d, div=%d\n",
+               rate, priv->min_div, ret, mult, div);
        return ret;
 }
 
@@ -107,6 +113,96 @@ static int clk_ti_am3_dpll_state(struct clk *clk, u8 state)
        return 0;
 }
 
+/**
+ * clk_ti_am3_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 clk_ti_am3_dpll_ssc_program(struct clk *clk)
+{
+       struct clk_ti_am3_dpll_priv *priv = dev_get_priv(clk->dev);
+       unsigned long ref_rate;
+       u32 v, ctrl, mod_freq_divider, exponent, mantissa;
+       u32 deltam_step, deltam_ceil;
+
+       ctrl = clk_ti_readl(&priv->clkmode_reg);
+
+       if (priv->ssc_modfreq && priv->ssc_deltam) {
+               ctrl |= CM_CLKMODE_DPLL_SSC_EN_MASK;
+
+               if (priv->ssc_downspread)
+                       ctrl |= CM_CLKMODE_DPLL_SSC_DOWNSPREAD_MASK;
+               else
+                       ctrl &= ~CM_CLKMODE_DPLL_SSC_DOWNSPREAD_MASK;
+
+               ref_rate = clk_get_rate(&priv->clk_ref);
+               mod_freq_divider =
+                   (ref_rate / priv->last_rounded_div) / (4 * priv->ssc_modfreq);
+               if (priv->ssc_modfreq > (ref_rate / 70))
+                       dev_warn(clk->dev,
+                                "clock: SSC modulation frequency of DPLL %s greater than %ld\n",
+                                clk->dev->name, ref_rate / 70);
+
+               exponent = 0;
+               mantissa = mod_freq_divider;
+               while ((mantissa > 127) && (exponent < 7)) {
+                       exponent++;
+                       mantissa /= 2;
+               }
+               if (mantissa > 127)
+                       mantissa = 127;
+
+               v = clk_ti_readl(&priv->ssc_modfreq_reg);
+               v &= ~(CM_SSC_MODFREQ_DPLL_MANT_MASK | CM_SSC_MODFREQ_DPLL_EXP_MASK);
+               v |= mantissa << __ffs(CM_SSC_MODFREQ_DPLL_MANT_MASK);
+               v |= exponent << __ffs(CM_SSC_MODFREQ_DPLL_EXP_MASK);
+               clk_ti_writel(v, &priv->ssc_modfreq_reg);
+               dev_dbg(clk->dev,
+                       "mod_freq_divider: %u, exponent: %u, mantissa: %u, modfreq_reg: 0x%x\n",
+                       mod_freq_divider, exponent, mantissa, v);
+
+               deltam_step = priv->last_rounded_mult * priv->ssc_deltam;
+               deltam_step /= 10;
+               if (priv->ssc_downspread)
+                       deltam_step /= 2;
+
+               deltam_step <<= __ffs(CM_SSC_DELTAM_DPLL_INT_MASK);
+               deltam_step /= 100;
+               deltam_step /= mod_freq_divider;
+               if (deltam_step > 0xFFFFF)
+                       deltam_step = 0xFFFFF;
+
+               deltam_ceil = (deltam_step & CM_SSC_DELTAM_DPLL_INT_MASK) >>
+                       __ffs(CM_SSC_DELTAM_DPLL_INT_MASK);
+               if (deltam_step & CM_SSC_DELTAM_DPLL_FRAC_MASK)
+                       deltam_ceil++;
+
+               if ((priv->ssc_downspread &&
+                    ((priv->last_rounded_mult - (2 * deltam_ceil)) < 20 ||
+                     priv->last_rounded_mult > 2045)) ||
+                   ((priv->last_rounded_mult - deltam_ceil) < 20 ||
+                    (priv->last_rounded_mult + deltam_ceil) > 2045))
+                       dev_warn(clk->dev,
+                                "clock: SSC multiplier of DPLL %s is out of range\n",
+                                clk->dev->name);
+
+               v = clk_ti_readl(&priv->ssc_deltam_reg);
+               v &= ~(CM_SSC_DELTAM_DPLL_INT_MASK | CM_SSC_DELTAM_DPLL_FRAC_MASK);
+               v |= deltam_step << __ffs(CM_SSC_DELTAM_DPLL_INT_MASK |
+                                         CM_SSC_DELTAM_DPLL_FRAC_MASK);
+               clk_ti_writel(v, &priv->ssc_deltam_reg);
+               dev_dbg(clk->dev,
+                       "deltam_step: %u, deltam_ceil: %u, deltam_reg: 0x%x\n",
+                       deltam_step, deltam_ceil, v);
+       } else {
+               ctrl &= ~CM_CLKMODE_DPLL_SSC_EN_MASK;
+       }
+
+       clk_ti_writel(ctrl, &priv->clkmode_reg);
+}
+
 static ulong clk_ti_am3_dpll_set_rate(struct clk *clk, ulong rate)
 {
        struct clk_ti_am3_dpll_priv *priv = dev_get_priv(clk->dev);
@@ -136,6 +232,8 @@ static ulong clk_ti_am3_dpll_set_rate(struct clk *clk, ulong rate)
 
        clk_ti_writel(v, &priv->clksel_reg);
 
+       clk_ti_am3_dpll_ssc_program(clk);
+
        /* lock dpll */
        clk_ti_am3_dpll_clken(priv, DPLL_EN_LOCK);
 
@@ -229,6 +327,7 @@ static int clk_ti_am3_dpll_of_to_plat(struct udevice *dev)
        struct clk_ti_am3_dpll_priv *priv = dev_get_priv(dev);
        struct clk_ti_am3_dpll_drv_data *data =
                (struct clk_ti_am3_dpll_drv_data *)dev_get_driver_data(dev);
+       u32 min_div;
        int err;
 
        priv->max_rate = data->max_rate;
@@ -251,6 +350,32 @@ static int clk_ti_am3_dpll_of_to_plat(struct udevice *dev)
                return err;
        }
 
+       err = clk_ti_get_reg_addr(dev, 3, &priv->ssc_deltam_reg);
+       if (err) {
+               dev_err(dev, "failed to get SSC deltam register\n");
+               return err;
+       }
+
+       err = clk_ti_get_reg_addr(dev, 4, &priv->ssc_modfreq_reg);
+       if (err) {
+               dev_err(dev, "failed to get SSC modfreq register\n");
+               return err;
+       }
+
+       if (dev_read_u32(dev, "ti,ssc-modfreq-hz", &priv->ssc_modfreq))
+               priv->ssc_modfreq = 0;
+
+       if (dev_read_u32(dev, "ti,ssc-deltam", &priv->ssc_deltam))
+               priv->ssc_deltam = 0;
+
+       priv->ssc_downspread = dev_read_bool(dev, "ti,ssc-downspread");
+
+       if (dev_read_u32(dev, "ti,min-div", &min_div) || min_div == 0 ||
+           min_div > 128)
+               priv->min_div = 1;
+       else
+               priv->min_div = min_div;
+
        return 0;
 }