drivers: mipi_dbi: stm32: get fmc frequency correctly

Use clock api to get correct FMC clock frequency.

Signed-off-by: Georgij Černyšiov <geo.cgv@gmail.com>

Author: GeorgeCGV

drivers/memc/memc_stm32.c

@@ -9,6 +9,7 @@
 
 #include <zephyr/drivers/clock_control/stm32_clock_control.h>
 #include <zephyr/drivers/pinctrl.h>
+#include <zephyr/drivers/memc/memc_stm32.h>
 
 #include <zephyr/logging/log.h>
 LOG_MODULE_REGISTER(memc_stm32, CONFIG_MEMC_LOG_LEVEL);
@@ -86,6 +87,28 @@ static int memc_stm32_init(const struct device *dev)
 	return 0;
 }
 
+int memc_stm32_fmc_clock_rate(uint32_t *freq)
+{
+	const struct device *dev = DEVICE_DT_GET_ONE(DT_DRV_COMPAT);
+	const struct memc_stm32_config *config = dev->config;
+
+	if (IS_ENABLED(STM32_FMC_DOMAIN_CLOCK_SUPPORT) && (config->pclk_len > 1)) {
+		if (clock_control_get_rate(DEVICE_DT_GET(STM32_CLOCK_CONTROL_NODE),
+					   (clock_control_subsys_t)&config->pclken[1],
+					   freq) < 0) {
+			return -EIO;
+		}
+	} else {
+		if (clock_control_get_rate(DEVICE_DT_GET(STM32_CLOCK_CONTROL_NODE),
+					   (clock_control_subsys_t)&config->pclken[0],
+					   freq) < 0) {
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
 PINCTRL_DT_INST_DEFINE(0);
 
 static const struct stm32_pclken pclken[] = STM32_DT_INST_CLOCKS(0);

drivers/mipi_dbi/mipi_dbi_stm32_fmc.c

@@ -9,6 +9,7 @@
 #include <zephyr/drivers/gpio.h>
 #include <zephyr/drivers/mipi_dbi.h>
 #include <zephyr/drivers/clock_control/stm32_clock_control.h>
+#include <zephyr/drivers/memc/memc_stm32.h>
 #include <zephyr/sys/barrier.h>
 #include <zephyr/sys/sys_io.h>
 #include <zephyr/sys/byteorder.h>
@@ -38,6 +39,7 @@ int mipi_dbi_stm32_fmc_check_config(const struct device *dev,
 	const struct mipi_dbi_stm32_fmc_config *config = dev->config;
 	struct mipi_dbi_stm32_fmc_data *data = dev->data;
 	uint32_t fmc_write_cycles;
+	uint32_t fmc_freq;
 
 	if (data->dbi_config == dbi_config) {
 		return 0;
@@ -53,14 +55,16 @@ int mipi_dbi_stm32_fmc_check_config(const struct device *dev,
 		return -EINVAL;
 	}
 
-	uint32_t hclk_freq =
-		STM32_AHB_PRESCALER * DT_PROP(STM32_CLOCK_CONTROL_NODE, clock_frequency);
+	if (memc_stm32_fmc_clock_rate(&fmc_freq) < 0) {
+		LOG_ERR("Unable to get FMC frequency");
+		return -EINVAL;
+	}
 
 	/* According to the FMC documentation*/
 	fmc_write_cycles =
 		((config->fmc_address_setup_time + 1) + (config->fmc_data_setup_time + 1)) * 1;
 
-	if (hclk_freq / fmc_write_cycles > dbi_config->config.frequency) {
+	if (fmc_freq / fmc_write_cycles > dbi_config->config.frequency) {
 		LOG_ERR("Frequency is too high for the display controller");
 		return -EINVAL;
 	}

include/zephyr/drivers/memc/memc_stm32.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) 2025 Georgij Cernysiov <geo.cgv@gmail.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_MEMC_STM32_H_
+#define ZEPHYR_INCLUDE_MEMC_STM32_H_
+
+int memc_stm32_fmc_clock_rate(uint32_t *rate);
+
+#endif /* ZEPHYR_INCLUDE_MEMC_STM32_H_ */