net: pse-pd: realtek-pse-mcu: add UART transport

Add the serdev (UART) transport for the Realtek PSE MCU core. It registers
the MCU as a serdev device and provides the send/recv callbacks the core
uses to exchange the 12-byte frames, receiving asynchronously via the
serdev receive_buf callback.

The baud rate defaults to 19200 and can be overridden per board with the
"current-speed" property.

Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>
Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
Link: https://patch.msgid.link/20260813222036.873930-5-jelonek.jonas@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/pse-pd/Kconfig

@@ -30,6 +30,17 @@ config PSE_REALTEK_MCU_I2C
 	  PSE silicon is not accessed directly. To compile this driver as a
 	  module, choose M here: the module will be called realtek-pse-mcu-i2c.
 
+config PSE_REALTEK_MCU_UART
+	tristate "Realtek PSE MCU driver (UART transport)"
+	depends on SERIAL_DEV_BUS
+	select PSE_REALTEK_MCU
+	help
+	  Driver for the microcontroller (MCU) that fronts the PSE
+	  hardware on various Realtek-based managed switches, attached
+	  via UART. The MCU exposes a message-based protocol; the actual PSE
+	  silicon is not accessed directly. To compile this driver as a
+	  module, choose M here: the module will be called realtek-pse-mcu-uart.
+
 config PSE_REGULATOR
 	tristate "Regulator based PSE controller"
 	help

drivers/net/pse-pd/Makefile

@@ -5,6 +5,7 @@ obj-$(CONFIG_PSE_CONTROLLER) += pse_core.o
 
 obj-$(CONFIG_PSE_REALTEK_MCU) += realtek-pse-mcu-core.o
 obj-$(CONFIG_PSE_REALTEK_MCU_I2C) += realtek-pse-mcu-i2c.o
+obj-$(CONFIG_PSE_REALTEK_MCU_UART) += realtek-pse-mcu-uart.o
 obj-$(CONFIG_PSE_REGULATOR) += pse_regulator.o
 obj-$(CONFIG_PSE_PD692X0) += pd692x0.o
 obj-$(CONFIG_PSE_SI3474) += si3474.o

drivers/net/pse-pd/realtek-pse-mcu-uart.c

@@ -0,0 +1,164 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <linux/cleanup.h>
+#include <linux/completion.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/pse-pd/pse.h>
+#include <linux/serdev.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+
+#include "realtek-pse-mcu.h"
+
+#define RTPSE_MCU_UART_BAUD_DEFAULT	19200
+#define RTPSE_MCU_UART_TX_TIMEOUT	msecs_to_jiffies(100)
+#define RTPSE_MCU_UART_RX_TIMEOUT	msecs_to_jiffies(RTPSE_MCU_RESPONSE_MAX_MS)
+
+struct rtpse_mcu_uart {
+	struct rtpse_mcu_ctrl pse;
+	struct serdev_device *serdev;
+	struct completion rx_done;
+	spinlock_t rx_lock;		/* protects rx_buf and rx_len */
+	size_t rx_len;
+	u8 rx_buf[RTPSE_MCU_MSG_SIZE];
+};
+
+#define to_rtpse_mcu_uart(p)  container_of(p, struct rtpse_mcu_uart, pse)
+
+/*
+ * No framing is done here: a glitched frame costs one transaction, then
+ * the next _send re-frames from rx_len 0. Resync works by returning count
+ * (not take), dropping any overflow so serdev keeps no leftover to bleed
+ * into the next frame.
+ */
+static size_t rtpse_mcu_uart_receive(struct serdev_device *serdev,
+				     const u8 *buf, size_t count)
+{
+	struct rtpse_mcu_uart *ctx = serdev_device_get_drvdata(serdev);
+	size_t take;
+
+	scoped_guard(spinlock_irqsave, &ctx->rx_lock) {
+		take = min(count, sizeof(ctx->rx_buf) - ctx->rx_len);
+		if (take) {
+			memcpy(ctx->rx_buf + ctx->rx_len, buf, take);
+			ctx->rx_len += take;
+			if (ctx->rx_len == sizeof(ctx->rx_buf))
+				complete(&ctx->rx_done);
+		}
+	}
+
+	/* consume all to avoid desync/misalignment */
+	return count;
+}
+
+static const struct serdev_device_ops rtpse_mcu_uart_serdev_ops = {
+	.receive_buf = rtpse_mcu_uart_receive,
+	.write_wakeup = serdev_device_write_wakeup,
+};
+
+static int rtpse_mcu_uart_send(struct rtpse_mcu_ctrl *pse, const struct rtpse_mcu_msg *req)
+{
+	struct rtpse_mcu_uart *ctx = to_rtpse_mcu_uart(pse);
+	int written;
+
+	/* clear any leftover rx state before transmitting */
+	scoped_guard(spinlock_irqsave, &ctx->rx_lock) {
+		reinit_completion(&ctx->rx_done);
+		ctx->rx_len = 0;
+	}
+
+	written = serdev_device_write(ctx->serdev, (const u8 *)req, sizeof(*req),
+				      RTPSE_MCU_UART_TX_TIMEOUT);
+	if (written < 0)
+		return written;
+	if (written != sizeof(*req))
+		return -EIO;
+
+	return 0;
+}
+
+static int rtpse_mcu_uart_recv(struct rtpse_mcu_ctrl *pse,
+			       const struct rtpse_mcu_msg *req,
+			       struct rtpse_mcu_msg *resp)
+{
+	struct rtpse_mcu_uart *ctx = to_rtpse_mcu_uart(pse);
+
+	if (!wait_for_completion_timeout(&ctx->rx_done, RTPSE_MCU_UART_RX_TIMEOUT))
+		return -ETIMEDOUT;
+
+	scoped_guard(spinlock_irqsave, &ctx->rx_lock) {
+		if (ctx->rx_len != sizeof(*resp))
+			return -EIO;
+
+		memcpy(resp, ctx->rx_buf, sizeof(*resp));
+	}
+	return 0;
+}
+
+static const struct rtpse_mcu_transport_ops rtpse_mcu_uart_transport_ops = {
+	.send = rtpse_mcu_uart_send,
+	.recv = rtpse_mcu_uart_recv,
+};
+
+static int rtpse_mcu_uart_probe(struct serdev_device *serdev)
+{
+	u32 speed = RTPSE_MCU_UART_BAUD_DEFAULT;
+	struct device *dev = &serdev->dev;
+	struct rtpse_mcu_uart *ctx;
+	unsigned int baud;
+	int ret;
+
+	ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
+	if (!ctx)
+		return -ENOMEM;
+
+	ctx->serdev = serdev;
+	ctx->pse.dev = dev;
+	ctx->pse.pcdev.owner = THIS_MODULE;
+	ctx->pse.transport = &rtpse_mcu_uart_transport_ops;
+	init_completion(&ctx->rx_done);
+	spin_lock_init(&ctx->rx_lock);
+
+	serdev_device_set_drvdata(serdev, ctx);
+	serdev_device_set_client_ops(serdev, &rtpse_mcu_uart_serdev_ops);
+
+	ret = devm_serdev_device_open(dev, serdev);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to open serdev\n");
+
+	fwnode_property_read_u32(dev_fwnode(dev), "current-speed", &speed);
+
+	baud = serdev_device_set_baudrate(serdev, speed);
+	if (baud != speed)
+		dev_warn(dev, "could not set baudrate %u, controller uses %u\n",
+			 speed, baud);
+
+	serdev_device_set_flow_control(serdev, false);
+
+	ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
+	if (ret)
+		dev_warn(dev, "could not set parity to none: %d\n", ret);
+
+	return rtpse_mcu_register(&ctx->pse);
+}
+
+static const struct of_device_id rtpse_mcu_uart_of_match[] = {
+	{ .compatible = "realtek,pse-mcu-gen1", .data = &rtpse_mcu_gen1_data },
+	{ .compatible = "realtek,pse-mcu-gen2", .data = &rtpse_mcu_gen2_data },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, rtpse_mcu_uart_of_match);
+
+static struct serdev_device_driver rtpse_mcu_uart_driver = {
+	.driver = {
+		.name = "realtek-pse-mcu-uart",
+		.of_match_table = rtpse_mcu_uart_of_match,
+	},
+	.probe  = rtpse_mcu_uart_probe,
+};
+module_serdev_device_driver(rtpse_mcu_uart_driver);
+
+MODULE_AUTHOR("Jonas Jelonek <jelonek.jonas@gmail.com>");
+MODULE_DESCRIPTION("Realtek PSE MCU driver (UART transport)");
+MODULE_LICENSE("GPL");