serial: stm32: get FIFO size from hwcfg register

Since STM32MP25, FIFO size could vary regarding the STM32MPxx version.
So we get this size from "hwcfgr1" register and compute threshold values
corresponding to the ratio given by reference manual.

As STM32MP1x, STM32MP25 and STM32H7 share the same compatible and STM32H7
doesn't have a register to get FIFO size, we force FIFO size to 16 in case
of zero read from hwcfgr1 register.

Signed-off-by: Valentin Caron <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/stm32-usart.c

···
 /* 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,
···
 		.has_swap = true,
 		.has_wakeup = true,
 		.has_fifo = true,
-		.fifosize = 16,
 	}
 };
 
···
 #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 void stm32_usart_get_ftcfg(struct platform_device *pdev, const char *p,
-				  int *ftcfg)
+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 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;
 
-	for (i = 0; i < ARRAY_SIZE(stm32h7_usart_fifo_thresh_cfg); i++)
-		if (stm32h7_usart_fifo_thresh_cfg[i] >= bytes)
+	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 (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)
···
 	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;
···
 
 	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))
···
 	if (!stm32port->port.uartclk) {
 		ret = -EINVAL;
 		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);

drivers/tty/serial/stm32-usart.h

···
 	u16 rdr;
 	u16 tdr;
 	u16 presc;
+	u16 hwcfgr1;
 };
 
 struct stm32_usart_config {
···
 	bool has_swap;
 	bool has_wakeup;
 	bool has_fifo;
-	int fifosize;
 };
 
 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     */