[PATCH v15 1/2] clk: scmi: fix SSC spread conversion

[PATCH v15 1/2] clk: scmi: fix SSC spread conversion

[Dario Binacchi]

The spread_bp field of struct clk_spread_spectrum holds the modulation
depth in permyriad (1/100 of a percent), as documented in
clk-provider.h and in the assigned-clock-sscs binding, while the i.MX
SCMI OEM extension expects a value in tenths of a percent, as pointed
out by Peng Fan.

The conversion divides spread_bp by 10000 instead of 10, as reported by
Sashiko, so any valid configuration is truncated to 0 and the hardware
is silently programmed with no spread at all.

Divide by 10 and fix the comment accordingly.

Fixes: 77369b1e6a37 ("clk: scmi: Add i.MX95 OEM extension support for SCMI clock driver")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/r/20260901155657.6A5981F00A3A@smtp.kernel.org
Reported-by: Peng Fan <peng.fan@nxp.com>
Closes: https://lore.kernel.org/r/ZR6PR04MB375776A27E98F140534E8F7FE488B62@ZR6PR04MB375776.eurprd04.prod.outlook.com
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>

---

Changes in v15:
 - Add Cc to stable.

Changes in v14:
 - Add Reviewed-by of Peng Fan

Changes in v13:
 - Divide spread_bp by 10 instead of 100 as requested by Peng Fan.
 - Rename the patch title and reword the description accordingly.
 - Add the Reported-by/Closes tags for Sashiko and Peng Fan.

 drivers/clk/clk-scmi-oem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/clk-scmi-oem.c b/drivers/clk/clk-scmi-oem.c
index be11d359b4ec..c1ebbdc6bbc5 100644
--- a/drivers/clk/clk-scmi-oem.c
+++ b/drivers/clk/clk-scmi-oem.c
@@ -39,12 +39,12 @@ scmi_clk_imx_set_spread_spectrum(struct clk_hw *hw,
 	u32 val;
 
 	/*
-	 * extConfigValue[7:0]   - spread percentage (%)
+	 * extConfigValue[7:0]   - spread percentage in tenths of a percent
 	 * extConfigValue[23:8]  - Modulation Frequency
 	 * extConfigValue[24]    - Enable/Disable
 	 * extConfigValue[31:25] - Reserved
 	 */
-	val = FIELD_PREP(SCMI_CLOCK_IMX_SS_PERCENTAGE_MASK, ss_conf->spread_bp / 10000);
+	val = FIELD_PREP(SCMI_CLOCK_IMX_SS_PERCENTAGE_MASK, ss_conf->spread_bp / 10);
 	val |= FIELD_PREP(SCMI_CLOCK_IMX_SS_MOD_FREQ_MASK, ss_conf->modfreq_hz);
 	if (ss_conf->method != CLK_SPREAD_NO)
 		val |= SCMI_CLOCK_IMX_SS_ENABLE_MASK;
-- 
2.43.0

Re: [PATCH v15 1/2] clk: scmi: fix SSC spread conversion

[Cristian Marussi]

On Wed, Nov 04, 2026 at 11:36:02AM +0100, Dario Binacchi wrote:
> The spread_bp field of struct clk_spread_spectrum holds the modulation
> depth in permyriad (1/100 of a percent), as documented in
> clk-provider.h and in the assigned-clock-sscs binding, while the i.MX
> SCMI OEM extension expects a value in tenths of a percent, as pointed
> out by Peng Fan.
> 
> The conversion divides spread_bp by 10000 instead of 10, as reported by
> Sashiko, so any valid configuration is truncated to 0 and the hardware
> is silently programmed with no spread at all.
> 
> Divide by 10 and fix the comment accordingly.
> 

LGTM.
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>

Thanks,
Cristian