rockchip/rk3399: enable DPLL SSC for DDR EMI test on bob

Spread Spectrum Modulator (SSMOD) is a fully-digital circuit used to
modulate the frequency of the Silicon Creations’ Fractional PLL in order
to reduce EMI.

We need to turn the DPLL spread spectrum feature on to
reduce the EMI noise for DDR on bob.

Change-Id: I75461d4235bcf55324e6664a1220754e770b4786
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>
Reviewed-on: https://review.coreboot.org/19557
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/mainboard/google/gru/Kconfig

@@ -38,6 +38,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select MAINBOARD_HAS_CHROMEOS
 	select MAINBOARD_HAS_NATIVE_VGA_INIT
 	select RAM_CODE_SUPPORT
+	select RK3399_SPREAD_SPECTRUM_DDR if BOARD_GOOGLE_BOB
 	select RTC
 	select SOC_ROCKCHIP_RK3399
 	select SPI_FLASH

src/soc/rockchip/rk3399/Kconfig

@@ -24,4 +24,12 @@ config PMIC_BUS
 	int
 	default -1
 
+config RK3399_SPREAD_SPECTRUM_DDR
+	bool "Spread-spectrum DDR clock"
+	default n
+	help
+	  Select Spread Spectrum Modulator (SSMOD) is a fully-digital circuit
+	  used to modulate the frequency of the Silicon Creations’ Fractional
+	  PLL in order to reduce EMI.
+
 endif

src/soc/rockchip/rk3399/clock.c

@@ -82,8 +82,23 @@ enum {
 	PLL_MODE_DEEP,
 	PLL_DSMPD_MASK			= 1,
 	PLL_DSMPD_SHIFT			= 3,
+	PLL_FRAC_MODE			= 0,
 	PLL_INTEGER_MODE		= 1,
 
+	/* PLL_CON4 */
+	PLL_SSMOD_BP_MASK		= 1,
+	PLL_SSMOD_BP_SHIFT		= 0,
+	PLL_SSMOD_DIS_SSCG_MASK		= 1,
+	PLL_SSMOD_DIS_SSCG_SHIFT	= 1,
+	PLL_SSMOD_RESET_MASK		= 1,
+	PLL_SSMOD_RESET_SHIFT		= 2,
+	PLL_SSMOD_DOWNSPEAD_MASK	= 1,
+	PLL_SSMOD_DOWNSPEAD_SHIFT	= 3,
+	PLL_SSMOD_DIVVAL_MASK		= 0Xf,
+	PLL_SSMOD_DIVVAL_SHIFT		= 4,
+	PLL_SSMOD_SPREADAMP_MASK	= 0x1f,
+	PLL_SSMOD_SPREADAMP_SHIFT	= 8,
+
 	/* PMUCRU_CLKSEL_CON0 */
 	PMU_PCLK_DIV_CON_MASK		= 0x1f,
 	PMU_PCLK_DIV_CON_SHIFT		= 0,
@@ -326,6 +341,83 @@ static void rkclk_set_pll(u32 *pll_con, const struct pll_div *div)
 					   PLL_MODE_NORM << PLL_MODE_SHIFT));
 }
 
+/*
+ * Configure the DPLL spread spectrum feature on memory clock.
+ * Configure sequence:
+ * 1. PLL been configured as frac mode, and DACPD should be set to 1’b0.
+ * 2. Configure DOWNSPERAD, SPREAD, DIVVAL(option: configure xPLL_CON5 with
+ *    extern wave table).
+ * 3. set ssmod_disable_sscg = 1’b0, and set ssmod_bp = 1’b0.
+ * 4. Assert RESET = 1’b1 to SSMOD.
+ * 5. RESET = 1’b0 on SSMOD.
+ * 6. Adjust SPREAD/DIVVAL/DOWNSPREAD.
+ */
+static void rkclk_set_dpllssc(struct pll_div *dpll_cfg)
+{
+	u32 divval;
+
+	/*
+	 * TODO find the root cause why is the delay needed, otherwise sometimes
+	 * hang somewhere with reboot tests.
+	 */
+	udelay(30);
+	assert(dpll_cfg->refdiv && dpll_cfg->refdiv <= 6);
+
+	/*
+	 * Need to acquire ~30kHZ which is the target modulation frequency.
+	 * The modulation frequency ~ 30kHz= OSC_HZ/revdiv/128/divval
+	 * (the 128 is the number points in the query table).
+	 */
+	divval = OSC_HZ / 128 / (30 * KHz) / dpll_cfg->refdiv;
+
+	/*
+	 * Use frac mode.
+	 * Make sure the output frequency isn't offset, set 0 for Fractional
+	 * part of feedback divide.
+	 */
+	write32(&cru_ptr->dpll_con[3],
+		RK_CLRSETBITS(PLL_DSMPD_MASK << PLL_DSMPD_SHIFT,
+			      PLL_FRAC_MODE << PLL_DSMPD_SHIFT));
+	clrsetbits_le32(&cru_ptr->dpll_con[2],
+			PLL_FRACDIV_MASK << PLL_FRACDIV_SHIFT,
+			0 << PLL_FRACDIV_SHIFT);
+
+	/*
+	 * Configure SSC divval.
+	 * Spread amplitude range = 0.1 * SPREAD[4:0] (%).
+	 * The below 8 means SPREAD[4:0] that appears to mitigate EMI on boards
+	 * tested. Center and down spread modulation amplitudes based on the
+	 * value of SPREAD.
+	 * SPREAD[4:0]	Center Spread	Down Spread
+	 *	0	0		0
+	 *	1	±0.1%		-0.10%
+	 *	2	±0.2%		-0.20%
+	 *	3	±0.3%		-0.30%
+	 *	4	±0.4%		-0.40%
+	 *	5	±0.5%		-0.50%
+	 *	...
+	 *	31	±3.1%		-3.10%
+	 */
+	write32(&cru_ptr->dpll_con[4],
+		RK_CLRSETBITS(PLL_SSMOD_DIVVAL_MASK << PLL_SSMOD_DIVVAL_SHIFT,
+			      divval << PLL_SSMOD_DIVVAL_SHIFT));
+	write32(&cru_ptr->dpll_con[4],
+		RK_CLRSETBITS(PLL_SSMOD_SPREADAMP_MASK <<
+			      PLL_SSMOD_SPREADAMP_SHIFT,
+			      8 << PLL_SSMOD_SPREADAMP_SHIFT));
+
+	/* Enable SSC for DPLL */
+	write32(&cru_ptr->dpll_con[4],
+		RK_CLRBITS(PLL_SSMOD_BP_MASK << PLL_SSMOD_BP_SHIFT |
+			   PLL_SSMOD_DIS_SSCG_MASK << PLL_SSMOD_DIS_SSCG_SHIFT));
+
+	/* Deassert reset SSMOD */
+	write32(&cru_ptr->dpll_con[4],
+		RK_CLRBITS(PLL_SSMOD_RESET_MASK << PLL_SSMOD_RESET_SHIFT));
+
+	udelay(20);
+}
+
 static int pll_para_config(u32 freq_hz, struct pll_div *div)
 {
 	u32 ref_khz = OSC_HZ / KHz, refdiv, fbdiv = 0;
@@ -571,6 +663,9 @@ void rkclk_configure_ddr(unsigned int hz)
 		die("Unsupported SDRAM frequency, add to clock.c!");
 	}
 	rkclk_set_pll(&cru_ptr->dpll_con[0], &dpll_cfg);
+
+	if (IS_ENABLED(CONFIG_RK3399_SPREAD_SPECTRUM_DDR))
+		rkclk_set_dpllssc(&dpll_cfg);
 }
 
 #define SPI_CLK_REG_VALUE(bus, clk_div) \