soc: arm: nxp_imx: fix flexspi frequency setting for iMXRT11xx SOC

Commit a10fee2 (drivers: clock_control: ccm_rev2: add support for
reclocking FlexSPI) introduced the ability to set the FlexSPI
clock frequency at runtime on RT11xx series SOCs. However, this
implementation resulted in the clock frequency being rounded up, not
down. This can result in flash clock frequency violations on some
flash parts, causing the system to crash when running in XIP mode.

Fixes #69088

Signed-off-by: Daniel DeGrasse <[email protected]>

Author: danieldegrasse

soc/arm/nxp_imx/rt/flexspi_rt11xx.c

@@ -38,8 +38,13 @@ uint32_t flexspi_clock_set_freq(uint32_t clock_name, uint32_t rate)
 			CLOCK_GetRootClockMux(flexspi_clk));
 	/* Get clock root frequency */
 	root_rate = CLOCK_GetFreq(root);
-	/* Select a divider based on root frequency */
-	divider = MIN((root_rate / rate), CCM_CLOCK_ROOT_CONTROL_DIV_MASK);
+	/* Select a divider based on root clock frequency. We round the
+	 * divider up, so that the resulting clock frequency is lower than
+	 * requested when we can't output the exact requested frequency
+	 */
+	divider = ((root_rate + (rate - 1)) / rate);
+	/* Cap divider to max value */
+	divider = MIN(divider, CCM_CLOCK_ROOT_CONTROL_DIV_MASK);
 
 	while (FLEXSPI_GetBusIdleStatus(flexspi) == false) {
 		/* Spin */