diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index e8ab5efad945..ffb2d4248107 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -39,63 +39,64 @@
 /* Register offsets */
 static struct stm32_usart_info __maybe_unused stm32f4_info = {
 	.ofs = {
-		.isr	= 0x00,
-		.rdr	= 0x04,
-		.tdr	= 0x04,
-		.brr	= 0x08,
-		.cr1	= 0x0c,
-		.cr2	= 0x10,
-		.cr3	= 0x14,
-		.gtpr	= 0x18,
-		.rtor	= UNDEF_REG,
-		.rqr	= UNDEF_REG,
-		.icr	= UNDEF_REG,
-		.presc	= UNDEF_REG,
+		.isr		= 0x00,
+		.rdr		= 0x04,
+		.tdr		= 0x04,
+		.brr		= 0x08,
+		.cr1		= 0x0c,
+		.cr2		= 0x10,
+		.cr3		= 0x14,
+		.gtpr		= 0x18,
+		.rtor		= UNDEF_REG,
+		.rqr		= UNDEF_REG,
+		.icr		= UNDEF_REG,
+		.presc		= UNDEF_REG,
+		.hwcfgr1	= UNDEF_REG,
 	},
 	.cfg = {
 		.uart_enable_bit = 13,
 		.has_7bits_data = false,
-		.fifosize = 1,
 	}
 };
 
 static struct stm32_usart_info __maybe_unused stm32f7_info = {
 	.ofs = {
-		.cr1	= 0x00,
-		.cr2	= 0x04,
-		.cr3	= 0x08,
-		.brr	= 0x0c,
-		.gtpr	= 0x10,
-		.rtor	= 0x14,
-		.rqr	= 0x18,
-		.isr	= 0x1c,
-		.icr	= 0x20,
-		.rdr	= 0x24,
-		.tdr	= 0x28,
-		.presc	= UNDEF_REG,
+		.cr1		= 0x00,
+		.cr2		= 0x04,
+		.cr3		= 0x08,
+		.brr		= 0x0c,
+		.gtpr		= 0x10,
+		.rtor		= 0x14,
+		.rqr		= 0x18,
+		.isr		= 0x1c,
+		.icr		= 0x20,
+		.rdr		= 0x24,
+		.tdr		= 0x28,
+		.presc		= UNDEF_REG,
+		.hwcfgr1	= UNDEF_REG,
 	},
 	.cfg = {
 		.uart_enable_bit = 0,
 		.has_7bits_data = true,
 		.has_swap = true,
-		.fifosize = 1,
 	}
 };
 
 static struct stm32_usart_info __maybe_unused stm32h7_info = {
 	.ofs = {
-		.cr1	= 0x00,
-		.cr2	= 0x04,
-		.cr3	= 0x08,
-		.brr	= 0x0c,
-		.gtpr	= 0x10,
-		.rtor	= 0x14,
-		.rqr	= 0x18,
-		.isr	= 0x1c,
-		.icr	= 0x20,
-		.rdr	= 0x24,
-		.tdr	= 0x28,
-		.presc	= 0x2c,
+		.cr1		= 0x00,
+		.cr2		= 0x04,
+		.cr3		= 0x08,
+		.brr		= 0x0c,
+		.gtpr		= 0x10,
+		.rtor		= 0x14,
+		.rqr		= 0x18,
+		.isr		= 0x1c,
+		.icr		= 0x20,
+		.rdr		= 0x24,
+		.tdr		= 0x28,
+		.presc		= 0x2c,
+		.hwcfgr1	= 0x3f0,
 	},
 	.cfg = {
 		.uart_enable_bit = 0,
@@ -103,7 +104,6 @@ static struct stm32_usart_info __maybe_unused stm32h7_info = {
 		.has_swap = true,
 		.has_wakeup = true,
 		.has_fifo = true,
-		.fifosize = 16,
 	}
 };
 
@@ -1497,37 +1497,57 @@ static const struct uart_ops stm32_uart_ops = {
 #endif /* CONFIG_CONSOLE_POLL */
 };
 
-/*
- * STM32H7 RX & TX FIFO threshold configuration (CR3 RXFTCFG / TXFTCFG)
- * Note: 1 isn't a valid value in RXFTCFG / TXFTCFG. In this case,
- * RXNEIE / TXEIE can be used instead of threshold irqs: RXFTIE / TXFTIE.
- * So, RXFTCFG / TXFTCFG bitfields values are encoded as array index + 1.
- */
-static const u32 stm32h7_usart_fifo_thresh_cfg[] = { 1, 2, 4, 8, 12, 14, 16 };
+struct stm32_usart_thresh_ratio {
+	int mul;
+	int div;
+};
+
+static const struct stm32_usart_thresh_ratio stm32h7_usart_fifo_thresh_cfg[] = {
+	{1, 8}, {1, 4}, {1, 2}, {3, 4}, {7, 8}, {1, 1} };
 
-static void stm32_usart_get_ftcfg(struct platform_device *pdev, const char *p,
-				  int *ftcfg)
+static int stm32_usart_get_thresh_value(u32 fifo_size, int index)
 {
-	u32 bytes, i;
+	return fifo_size * stm32h7_usart_fifo_thresh_cfg[index].mul /
+		stm32h7_usart_fifo_thresh_cfg[index].div;
+}
 
-	/* DT option to get RX & TX FIFO threshold (default to 8 bytes) */
+static int stm32_usart_get_ftcfg(struct platform_device *pdev, struct stm32_port *stm32port,
+				 const char *p, int *ftcfg)
+{
+	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
+	u32 bytes, i, cfg8;
+	int fifo_size;
+
+	if (WARN_ON(ofs->hwcfgr1 == UNDEF_REG))
+		return 1;
+
+	cfg8 = FIELD_GET(USART_HWCFGR1_CFG8,
+			 readl_relaxed(stm32port->port.membase + ofs->hwcfgr1));
+
+	/* On STM32H7, hwcfgr is not present, so returned value will be 0 */
+	fifo_size = cfg8 ? 1 << cfg8 : STM32H7_USART_FIFO_SIZE;
+
+	/* DT option to get RX & TX FIFO threshold (default to half fifo size) */
 	if (of_property_read_u32(pdev->dev.of_node, p, &bytes))
-		bytes = 8;
+		bytes = fifo_size / 2;
+
+	if (bytes < stm32_usart_get_thresh_value(fifo_size, 0)) {
+		*ftcfg = -EINVAL;
+		return fifo_size;
+	}
 
-	for (i = 0; i < ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg); i++)
-		if (stm32h7_usart_fifo_thresh_cfg[i] >= bytes)
+	for (i = 0; i < ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg); i++) {
+		if (stm32_usart_get_thresh_value(fifo_size, i) >= bytes)
 			break;
+	}
 	if (i >= ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg))
 		i = ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg) - 1;
 
-	dev_dbg(&pdev->dev, "%s set to %d bytes\n", p,
-		stm32h7_usart_fifo_thresh_cfg[i]);
+	dev_dbg(&pdev->dev, "%s set to %d/%d bytes\n", p,
+		stm32_usart_get_thresh_value(fifo_size, i), fifo_size);
 
-	/* Provide FIFO threshold ftcfg (1 is invalid: threshold irq unused) */
-	if (i)
-		*ftcfg = i - 1;
-	else
-		*ftcfg = -EINVAL;
+	*ftcfg = i;
+	return fifo_size;
 }
 
 static void stm32_usart_deinit_port(struct stm32_port *stm32port)
@@ -1557,7 +1577,6 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
 	port->flags	= UPF_BOOT_AUTOCONF;
 	port->ops	= &stm32_uart_ops;
 	port->dev	= &pdev->dev;
-	port->fifosize	= stm32port->info->cfg.fifosize;
 	port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_STM32_CONSOLE);
 	port->irq = irq;
 	port->rs485_config = stm32_usart_config_rs485;
@@ -1573,14 +1592,6 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
 	stm32port->swap = stm32port->info->cfg.has_swap &&
 		of_property_read_bool(pdev->dev.of_node, "rx-tx-swap");
 
-	stm32port->fifoen = stm32port->info->cfg.has_fifo;
-	if (stm32port->fifoen) {
-		stm32_usart_get_ftcfg(pdev, "rx-threshold",
-				      &stm32port->rxftcfg);
-		stm32_usart_get_ftcfg(pdev, "tx-threshold",
-				      &stm32port->txftcfg);
-	}
-
 	port->membase = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
 	if (IS_ERR(port->membase))
 		return PTR_ERR(port->membase);
@@ -1603,6 +1614,15 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
 		goto err_clk;
 	}
 
+	stm32port->fifoen = stm32port->info->cfg.has_fifo;
+	if (stm32port->fifoen) {
+		stm32_usart_get_ftcfg(pdev, stm32port, "rx-threshold", &stm32port->rxftcfg);
+		port->fifosize = stm32_usart_get_ftcfg(pdev, stm32port, "tx-threshold",
+						       &stm32port->txftcfg);
+	} else {
+		port->fifosize = 1;
+	}
+
 	stm32port->gpios = mctrl_gpio_init(&stm32port->port, 0);
 	if (IS_ERR(stm32port->gpios)) {
 		ret = PTR_ERR(stm32port->gpios);
diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index bf3720948704..af20258ccc7a 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -21,6 +21,7 @@ struct stm32_usart_offsets {
 	u16 rdr;
 	u16 tdr;
 	u16 presc;
+	u16 hwcfgr1;
 };
 
 struct stm32_usart_config {
@@ -29,7 +30,6 @@ struct stm32_usart_config {
 	bool has_swap;
 	bool has_wakeup;
 	bool has_fifo;
-	int fifosize;
 };
 
 struct stm32_usart_info {
@@ -182,8 +182,12 @@ struct stm32_usart_info {
 #define USART_PRESC		GENMASK(3, 0)	/* H7 */
 #define USART_PRESC_MAX		0b1011
 
+/* USART_HWCFCR1 */
+#define USART_HWCFGR1_CFG8	GENMASK(31, 28)	/* MP1 */
+
 #define STM32_SERIAL_NAME "ttySTM"
 #define STM32_MAX_PORTS 9
+#define STM32H7_USART_FIFO_SIZE 16
 
 #define RX_BUF_L 4096		 /* dma rx buffer length     */
 #define RX_BUF_P (RX_BUF_L / 2)	 /* dma rx buffer period     */
