kcs_bmc_serio acts as a bridge between the KCS drivers in the IPMI
subsystem and the existing userspace interfaces available through the
serio subsystem. This is useful when userspace would like to make use of
the BMC KCS devices for purposes that aren't IPMI.

Signed-off-by: Andrew Jeffery <redacted>
---
drivers/char/ipmi/Kconfig         |  14 +++
drivers/char/ipmi/Makefile        |   1 +
drivers/char/ipmi/kcs_bmc_serio.c | 151 ++++++++++++++++++++++++++++++
3 files changed, 166 insertions(+)
create mode 100644 drivers/char/ipmi/kcs_bmc_serio.c

diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
index bc5f81899b62..249b31197eea 100644
--- a/drivers/char/ipmi/Kconfig
+++ b/drivers/char/ipmi/Kconfig

@@ -137,6 +137,20 @@ config IPMI_KCS_BMC_CDEV_IPMI

	  This support is also available as a module. The module will be
	  called kcs_bmc_cdev_ipmi.

+config IPMI_KCS_BMC_SERIO
+	depends on IPMI_KCS_BMC && SERIO
+	tristate "SerIO adaptor for BMC KCS devices"
+	help
+	  Adapts the BMC KCS device for the SerIO subsystem. This allows users
+	  to take advantage of userspace interfaces provided by SerIO where
+	  appropriate.
+
+	  Say YES if you wish to expose KCS devices on the BMC via SerIO
+	  interfaces.
+
+	  This support is also available as a module. The module will be
+	  called kcs_bmc_serio.
+
config ASPEED_BT_IPMI_BMC
	depends on ARCH_ASPEED || COMPILE_TEST
	depends on REGMAP && REGMAP_MMIO && MFD_SYSCON

diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
index fcfa676afddb..84f47d18007f 100644
--- a/drivers/char/ipmi/Makefile
+++ b/drivers/char/ipmi/Makefile

@@ -23,6 +23,7 @@ obj-$(CONFIG_IPMI_POWERNV) += ipmi_powernv.o

obj-$(CONFIG_IPMI_WATCHDOG) += ipmi_watchdog.o
obj-$(CONFIG_IPMI_POWEROFF) += ipmi_poweroff.o
obj-$(CONFIG_IPMI_KCS_BMC) += kcs_bmc.o
+obj-$(CONFIG_IPMI_KCS_BMC_SERIO) += kcs_bmc_serio.o
obj-$(CONFIG_IPMI_KCS_BMC_CDEV_IPMI) += kcs_bmc_cdev_ipmi.o
obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o

diff --git a/drivers/char/ipmi/kcs_bmc_serio.c b/drivers/char/ipmi/kcs_bmc_serio.c
new file mode 100644
index 000000000000..30a2b7ab464b
--- /dev/null
+++ b/drivers/char/ipmi/kcs_bmc_serio.c

@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Copyright (c) 2021 IBM Corp. */
+
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/sched/signal.h>
+#include <linux/serio.h>
+#include <linux/slab.h>
+
+#include "kcs_bmc_client.h"
+
+struct kcs_bmc_serio {
+	struct list_head entry;
+
+	struct kcs_bmc_client client;
+	struct serio *port;
+
+	spinlock_t lock;
+};
+
+static inline struct kcs_bmc_serio *client_to_kcs_bmc_serio(struct kcs_bmc_client *client)
+{
+	return container_of(client, struct kcs_bmc_serio, client);
+}
+
+static irqreturn_t kcs_bmc_serio_event(struct kcs_bmc_client *client)
+{
+	struct kcs_bmc_serio *priv;
+	u8 handled = IRQ_NONE;
+	u8 status;
+
+	priv = client_to_kcs_bmc_serio(client);
+
+	spin_lock(&priv->lock);
+
+	status = kcs_bmc_read_status(client->dev);
+
+	if (status & KCS_BMC_STR_IBF)
+		handled = serio_interrupt(priv->port, kcs_bmc_read_data(client->dev), 0);
+
+	spin_unlock(&priv->lock);
+
+	return handled;
+}
+
+static const struct kcs_bmc_client_ops kcs_bmc_serio_client_ops = {
+	.event = kcs_bmc_serio_event,
+};
+
+static int kcs_bmc_serio_open(struct serio *port)
+{
+	struct kcs_bmc_serio *priv = port->port_data;
+
+	return kcs_bmc_enable_device(priv->client.dev, &priv->client);
+}
+
+static void kcs_bmc_serio_close(struct serio *port)
+{
+	struct kcs_bmc_serio *priv = port->port_data;
+
+	kcs_bmc_disable_device(priv->client.dev, &priv->client);
+}
+
+static DEFINE_SPINLOCK(kcs_bmc_serio_instances_lock);
+static LIST_HEAD(kcs_bmc_serio_instances);
+
+static int kcs_bmc_serio_add_device(struct kcs_bmc_device *kcs_bmc)
+{
+	struct kcs_bmc_serio *priv;
+	struct serio *port;
+
+	priv = devm_kzalloc(kcs_bmc->dev, sizeof(*priv), GFP_KERNEL);
+	port = kzalloc(sizeof(*port), GFP_KERNEL);