[PATCH 3/3] clk: scmi: Support Spread Spectrum for NXP i.MX95

From: Peng Fan <peng.fan@nxp.com>
Date: 2025-08-12 12:18:49
Also in: arm-scmi, linux-clk, lkml
Subsystem: common clk framework, system control & power/management interface (scpi/scmi) message protocol drivers, the rest · Maintainers: Michael Turquette, Stephen Boyd, Sudeep Holla, Linus Torvalds

The PLL clocks on NXP i.MX95 SoCs support Spread Spectrum (SS).
This patch introduces scmi_clk_imx_set_spread_spectrum to pass SS
configuration to the SCMI firmware, which handles the actual
implementation.

To ensure this feature is only enabled on NXP platforms,
scmi_clk_imx_extended_config_oem is added. Since SS is only applicable
to PLL clocks, config_oem_get is used to verify SS support for a given
clock.

i.MX95 SCMI firmware Spread Spectrum extConfigValue definition is as
below, no modulation method because firmware forces to use down spread.
	 extConfigValue[7:0]   - spread percentage (%)
	 extConfigValue[23:8]  - Modulation Frequency (KHz)
	 extConfigValue[24]    - Enable/Disable
	 extConfigValue[31:25] - Reserved

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/clk/clk-scmi.c        | 64 ++++++++++++++++++++++++++++++++++++++++---
 include/linux/scmi_protocol.h |  5 ++++
 2 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/clk-scmi.c b/drivers/clk/clk-scmi.c
index d2408403283fc72f0cf902e65f4c08bcbc7b4b0b..bb5e20dab18e92932ab4b99192b496e0c4d96417 100644
--- a/drivers/clk/clk-scmi.c
+++ b/drivers/clk/clk-scmi.c

@@ -12,6 +12,7 @@
 #include <linux/of.h>
 #include <linux/module.h>
 #include <linux/scmi_protocol.h>
+#include <linux/scmi_imx_protocol.h>
 #include <asm/div64.h>
 
 #define NOT_ATOMIC	false

@@ -23,6 +24,7 @@ enum scmi_clk_feats {
 	SCMI_CLK_RATE_CTRL_SUPPORTED,
 	SCMI_CLK_PARENT_CTRL_SUPPORTED,
 	SCMI_CLK_DUTY_CYCLE_SUPPORTED,
+	SCMI_CLK_IMX_SSC_SUPPORTED,
 	SCMI_CLK_FEATS_COUNT
 };

@@ -98,6 +100,35 @@ static int scmi_clk_set_parent(struct clk_hw *hw, u8 parent_index)
 	return scmi_proto_clk_ops->parent_set(clk->ph, clk->id, parent_index);
 }
 
+static int scmi_clk_imx_set_spread_spectrum(struct clk_hw *hw,
+					    struct clk_spread_spectrum *clk_ss)
+{
+	struct scmi_clk *clk = to_scmi_clk(hw);
+	int ret;
+	u32 val;
+
+	/*
+	 * extConfigValue[7:0]   - spread percentage (%)
+	 * extConfigValue[23:8]  - Modulation Frequency
+	 * extConfigValue[24]    - Enable/Disable
+	 * extConfigValue[31:25] - Reserved
+	 */
+	val = FIELD_PREP(SCMI_CLOCK_IMX_SS_PERCENTAGE_MASK, clk_ss->spread_bp / 10000);
+	val |= FIELD_PREP(SCMI_CLOCK_IMX_SS_MOD_FREQ_MASK, clk_ss->modfreq_hz);
+	if (clk_ss->method != CLK_SSC_NO_SPREAD)
+		val |= SCMI_CLOCK_IMX_SS_ENABLE_MASK;
+	ret = scmi_proto_clk_ops->config_oem_set(clk->ph, clk->id,
+						 SCMI_CLOCK_CFG_IMX_SSC,
+						 val, false);
+	if (ret)
+		dev_warn(clk->dev,
+			 "Failed to set spread spectrum(%u,%u,%u) for clock ID %d\n",
+			 clk_ss->modfreq_hz, clk_ss->spread_bp, clk_ss->method,
+			 clk->id);
+
+	return ret;
+}
+
 static u8 scmi_clk_get_parent(struct clk_hw *hw)
 {
 	struct scmi_clk *clk = to_scmi_clk(hw);

@@ -316,11 +347,33 @@ scmi_clk_ops_alloc(struct device *dev, unsigned long feats_key)
 		ops->set_duty_cycle = scmi_clk_set_duty_cycle;
 	}
 
+	if (feats_key & BIT(SCMI_CLK_IMX_SSC_SUPPORTED))
+		ops->set_spread_spectrum = scmi_clk_imx_set_spread_spectrum;
+
 	return ops;
 }
 
+static void scmi_clk_imx_extended_config_oem(const struct scmi_handle *handle,
+					     struct scmi_clk *sclk,
+					     unsigned int *feats_key)
+{
+	int ret;
+	u32 val;
+
+	if (strcmp(handle->version->vendor_id, SCMI_IMX_VENDOR) ||
+	    strcmp(handle->version->sub_vendor_id, SCMI_IMX_SUBVENDOR))
+		return;
+
+	ret = scmi_proto_clk_ops->config_oem_get(sclk->ph, sclk->id,
+						 SCMI_CLOCK_CFG_IMX_SSC,
+						 &val, NULL, false);
+	if (!ret)
+		*feats_key |= BIT(SCMI_CLK_IMX_SSC_SUPPORTED);
+}
+
 /**
  * scmi_clk_ops_select() - Select a proper set of clock operations
+ * @handle: A reference to an SCMI entity
  * @sclk: A reference to an SCMI clock descriptor
  * @atomic_capable: A flag to indicate if atomic mode is supported by the
  *		    transport

@@ -345,8 +398,8 @@ scmi_clk_ops_alloc(struct device *dev, unsigned long feats_key)
  *	   NULL otherwise.
  */
 static const struct clk_ops *
-scmi_clk_ops_select(struct scmi_clk *sclk, bool atomic_capable,
-		    unsigned int atomic_threshold_us,
+scmi_clk_ops_select(const struct scmi_handle *handle, struct scmi_clk *sclk,
+		    bool atomic_capable, unsigned int atomic_threshold_us,
 		    const struct clk_ops **clk_ops_db, size_t db_size)
 {
 	const struct scmi_clock_info *ci = sclk->info;

@@ -370,9 +423,12 @@ scmi_clk_ops_select(struct scmi_clk *sclk, bool atomic_capable,
 	if (!ci->parent_ctrl_forbidden)
 		feats_key |= BIT(SCMI_CLK_PARENT_CTRL_SUPPORTED);
 
-	if (ci->extended_config)
+	if (ci->extended_config) {
 		feats_key |= BIT(SCMI_CLK_DUTY_CYCLE_SUPPORTED);
 
+		scmi_clk_imx_extended_config_oem(handle, sclk, &feats_key);
+	}
+
 	if (WARN_ON(feats_key >= db_size))
 		return NULL;

@@ -459,7 +515,7 @@ static int scmi_clocks_probe(struct scmi_device *sdev)
 		 * to avoid sharing the devm_ allocated clk_ops between multiple
 		 * SCMI clk driver instances.
 		 */
-		scmi_ops = scmi_clk_ops_select(sclk, transport_is_atomic,
+		scmi_ops = scmi_clk_ops_select(handle, sclk, transport_is_atomic,
 					       atomic_threshold_us,
 					       scmi_clk_ops_db,
 					       ARRAY_SIZE(scmi_clk_ops_db));

diff --git a/include/linux/scmi_protocol.h b/include/linux/scmi_protocol.h
index 688466a0e816247d24704f7ba109667a14226b67..6f9f197ee671540e38470a5666eb5ba8ec9de439 100644
--- a/include/linux/scmi_protocol.h
+++ b/include/linux/scmi_protocol.h

@@ -80,9 +80,14 @@ enum scmi_clock_oem_config {
 	SCMI_CLOCK_CFG_DUTY_CYCLE = 0x1,
 	SCMI_CLOCK_CFG_PHASE,
 	SCMI_CLOCK_CFG_OEM_START = 0x80,
+	SCMI_CLOCK_CFG_IMX_SSC = 0x80,
 	SCMI_CLOCK_CFG_OEM_END = 0xFF,
 };
 
+#define SCMI_CLOCK_IMX_SS_PERCENTAGE_MASK	GENMASK(7, 0)
+#define SCMI_CLOCK_IMX_SS_MOD_FREQ_MASK		GENMASK(23, 8)
+#define SCMI_CLOCK_IMX_SS_ENABLE_MASK		BIT(24)
+
 /**
  * struct scmi_clk_proto_ops - represents the various operations provided
  *	by SCMI Clock Protocol

-- 
2.37.1

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