On Fri, 21 May 2021, at 16:50, Zev Weiss wrote:

On Mon, May 10, 2021 at 12:42:08AM CDT, Andrew Jeffery wrote:

quoted

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);

Is there a particular reason to allocate port with a raw kzalloc()
instead of another devm_kzalloc()?

Yes, because it causes pointer confusion on remove. We get the following backtrace:

[   95.018845] Backtrace: 
[   95.019162] [<802e1fb0>] (___cache_free) from [<802e31cc>] (kfree+0xc0/0x1e8)
[   95.019658]  r10:00000081 r9:8667c000 r8:80100284 r7:81000b40 r6:a0000013 r5:80640bd4
[   95.020032]  r4:82a5ec40
[   95.020206] [<802e310c>] (kfree) from [<80640bd4>] (serio_release_port+0x1c/0x28)
[   95.020571]  r7:00000000 r6:819c1540 r5:86acf480 r4:82a5ed70
[   95.020818] [<80640bb8>] (serio_release_port) from [<80565e00>] (device_release+0x40/0xb4)
[   95.021387] [<80565dc0>] (device_release) from [<804a0bcc>] (kobject_put+0xc8/0x210)
[   95.021961]  r5:80c77c30 r4:82a5ed70
[   95.022141] [<804a0b04>] (kobject_put) from [<80566078>] (put_device+0x20/0x24)
[   95.022537]  r7:80c820cc r6:82a5ec40 r5:80c820e4 r4:82a5ed70
[   95.023017] [<80566058>] (put_device) from [<80640a58>] (serio_destroy_port+0x12c/0x140)
[   95.023719] [<8064092c>] (serio_destroy_port) from [<80640b3c>] (serio_unregister_port+0x34/0x44)
[   95.024326]  r7:7f0012b4 r6:7f002024 r5:80c820e4 r4:82a5ec40
[   95.024792] [<80640b08>] (serio_unregister_port) from [<7f0100b8>] (kcs_bmc_serio_remove_device+0x90/0xbc [kcs_bmc_serio])
[   95.026951]  r5:8668b7c0 r4:86acf0c0
[   95.027390] [<7f010028>] (kcs_bmc_serio_remove_device [kcs_bmc_serio]) from [<7f00048c>] (kcs_bmc_unregister_driver+0x60/0xbd4 [kcs_bmc])
[   95.028443]  r5:7f012018 r4:8668b7c0
[   95.028634] [<7f00042c>] (kcs_bmc_unregister_driver [kcs_bmc]) from [<7f0102c4>] (kcs_bmc_serio_exit+0x1c/0xd58 [kcs_bmc_serio])
[   95.029165]  r7:00000081 r6:80cd0dac r5:00000000 r4:7f012040
[   95.029397] [<7f0102a8>] (kcs_bmc_serio_exit [kcs_bmc_serio]) from [<801cbab0>] (sys_delete_module+0x140/0x280)
[   95.029875] [<801cb970>] (sys_delete_module) from [<80100080>] (ret_fast_syscall+0x0/0x58)

quoted

+	if (!(priv && port))
+		return -ENOMEM;
+
+	port->id.type = SERIO_8042;
+	port->open = kcs_bmc_serio_open;
+	port->close = kcs_bmc_serio_close;
+	port->port_data = priv;
+	port->dev.parent = kcs_bmc->dev;
+
+	spin_lock_init(&priv->lock);
+	priv->port = port;
+	priv->client.dev = kcs_bmc;
+	priv->client.ops = &kcs_bmc_serio_client_ops;
+
+	spin_lock_irq(&kcs_bmc_serio_instances_lock);
+	list_add(&priv->entry, &kcs_bmc_serio_instances);
+	spin_unlock_irq(&kcs_bmc_serio_instances_lock);
+
+	serio_register_port(port);
+
+	dev_info(kcs_bmc->dev, "Initialised serio client for channel %d", kcs_bmc->channel);
+
+	return 0;
+}
+
+static int kcs_bmc_serio_remove_device(struct kcs_bmc_device *kcs_bmc)
+{
+	struct kcs_bmc_serio *priv = NULL, *pos;
+
+	spin_lock_irq(&kcs_bmc_serio_instances_lock);
+	list_for_each_entry(pos, &kcs_bmc_serio_instances, entry) {
+		if (pos->client.dev == kcs_bmc) {
+			priv = pos;
+			list_del(&pos->entry);
+			break;
+		}
+	}
+	spin_unlock_irq(&kcs_bmc_serio_instances_lock);
+
+	if (!priv)
+		return -ENODEV;
+
+	serio_unregister_port(priv->port);
+	kcs_bmc_disable_device(kcs_bmc, &priv->client);
+	devm_kfree(priv->client.dev->dev, priv);

Looks like the priv->port allocation would leak here I think?

No, because port's released through serio_unregister_port(). It's not super obvious though, so I'll add a comment next to the kzalloc().

Also, is the asymmetry of having kcs_bmc_disable_device() here but no
corresponding kcs_bmc_enable_device() in kcs_bmc_serio_add_device()
intentional?  If so, an explanatory comment of some sort might be nice
to add.

It's intentional to make sure the device isn't left registered as enabled in the core. kcs_bmc_enable_device() is called in the open() path.

Andrew