Subject: Re: [PATCH v2 13/21] ipmi: kcs_bmc: Decouple the IPMI chardev from the core

From: Zev Weiss <[email-masked]>
Date: Fri, 9 Apr 2021 04:35:30 +0000

On Fri, Mar 19, 2021 at 01:27:44AM CDT, Andrew Jeffery wrote:
>Now that we have untangled the data-structures, split the userspace
>interface out into its own module. Userspace interfaces and drivers are
>registered to the KCS BMC core to support arbitrary binding of either.
>
>Signed-off-by: Andrew Jeffery <[email-masked]>
>---
> drivers/char/ipmi/Kconfig             | 13 +++++
> drivers/char/ipmi/Makefile            |  3 +-
> drivers/char/ipmi/kcs_bmc.c           | 78 ++++++++++++++++++++++++++-
> drivers/char/ipmi/kcs_bmc.h           |  4 --
> drivers/char/ipmi/kcs_bmc_cdev_ipmi.c | 33 +++++++++---
> drivers/char/ipmi/kcs_bmc_client.h    | 14 +++++
> 6 files changed, 132 insertions(+), 13 deletions(-)
>
>diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
>index 07847d9a459a..bc5f81899b62 100644
>--- a/drivers/char/ipmi/Kconfig
>+++ b/drivers/char/ipmi/Kconfig
>@@ -124,6 +124,19 @@ config NPCM7XX_KCS_IPMI_BMC
> 	  This support is also available as a module.  If so, the module
> 	  will be called kcs_bmc_npcm7xx.
>
>+config IPMI_KCS_BMC_CDEV_IPMI
>+	depends on IPMI_KCS_BMC
>+	tristate "IPMI character device interface for BMC KCS devices"
>+	help
>+	  Provides a BMC-side character device implementing IPMI
>+	  semantics for KCS IPMI devices.
>+
>+	  Say YES if you wish to expose KCS devices on the BMC for IPMI
>+	  purposes.
>+
>+	  This support is also available as a module. The module will be
>+	  called kcs_bmc_cdev_ipmi.
>+
> 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 a302bc865370..fcfa676afddb 100644
>--- a/drivers/char/ipmi/Makefile
>+++ b/drivers/char/ipmi/Makefile
>@@ -22,7 +22,8 @@ obj-$(CONFIG_IPMI_SSIF) += ipmi_ssif.o
> obj-$(CONFIG_IPMI_POWERNV) += ipmi_powernv.o
> obj-$(CONFIG_IPMI_WATCHDOG) += ipmi_watchdog.o
> obj-$(CONFIG_IPMI_POWEROFF) += ipmi_poweroff.o
>-obj-$(CONFIG_IPMI_KCS_BMC) += kcs_bmc.o kcs_bmc_cdev_ipmi.o
>+obj-$(CONFIG_IPMI_KCS_BMC) += kcs_bmc.o
>+obj-$(CONFIG_IPMI_KCS_BMC_CDEV_IPMI) += kcs_bmc_cdev_ipmi.o
> obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
> obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
> obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
>diff --git a/drivers/char/ipmi/kcs_bmc.c b/drivers/char/ipmi/kcs_bmc.c
>index 266ebec71d6f..694db6ee2a92 100644
>--- a/drivers/char/ipmi/kcs_bmc.c
>+++ b/drivers/char/ipmi/kcs_bmc.c
>@@ -5,7 +5,9 @@
>  */
>
> #include <linux/device.h>
>+#include <linux/list.h>
> #include <linux/module.h>
>+#include <linux/mutex.h>
>
> #include "kcs_bmc.h"
>
>@@ -13,6 +15,11 @@
> #include "kcs_bmc_device.h"
> #include "kcs_bmc_client.h"
>
>+/* Record probed devices and cdevs */
>+static DEFINE_MUTEX(kcs_bmc_lock);
>+static LIST_HEAD(kcs_bmc_devices);
>+static LIST_HEAD(kcs_bmc_cdevs);
>+
> /* Consumer data access */
>
> u8 kcs_bmc_read_data(struct kcs_bmc_device *kcs_bmc)
>@@ -100,16 +107,83 @@ EXPORT_SYMBOL(kcs_bmc_disable_device);
>
> int kcs_bmc_add_device(struct kcs_bmc_device *kcs_bmc)
> {
>-	return kcs_bmc_ipmi_attach_cdev(kcs_bmc);
>+	struct kcs_bmc_cdev *cdev;
>+	int rc;
>+
>+	spin_lock_init(&kcs_bmc->lock);
>+	kcs_bmc->client = NULL;
>+
>+	mutex_lock(&kcs_bmc_lock);
>+	list_add(&kcs_bmc->entry, &kcs_bmc_devices);
>+	list_for_each_entry(cdev, &kcs_bmc_cdevs, entry) {
>+		rc = cdev->ops->add_device(kcs_bmc);
>+		if (rc)
>+			dev_err(kcs_bmc->dev, "Failed to add chardev for KCS channel %d: %d",
>+				kcs_bmc->channel, rc);
>+	}
>+	mutex_unlock(&kcs_bmc_lock);
>+
>+	return 0;

We're ignoring failed ->add_device() calls here?

> }
> EXPORT_SYMBOL(kcs_bmc_add_device);
>
> int kcs_bmc_remove_device(struct kcs_bmc_device *kcs_bmc)
> {
>-	return kcs_bmc_ipmi_detach_cdev(kcs_bmc);
>+	struct kcs_bmc_cdev *cdev;
>+	int rc;
>+
>+	mutex_lock(&kcs_bmc_lock);
>+	list_del(&kcs_bmc->entry);
>+	list_for_each_entry(cdev, &kcs_bmc_cdevs, entry) {
>+		rc = cdev->ops->remove_device(kcs_bmc);
>+		if (rc)
>+			dev_err(kcs_bmc->dev, "Failed to remove chardev for KCS channel %d: %d",
>+				kcs_bmc->channel, rc);
>+	}
>+	mutex_unlock(&kcs_bmc_lock);
>+
>+	return 0;

Similarly with the return value here...

> }
> EXPORT_SYMBOL(kcs_bmc_remove_device);
>
>+int kcs_bmc_register_cdev(struct kcs_bmc_cdev *cdev)
>+{
>+	struct kcs_bmc_device *kcs_bmc;
>+	int rc;
>+
>+	mutex_lock(&kcs_bmc_lock);
>+	list_add(&cdev->entry, &kcs_bmc_cdevs);
>+	list_for_each_entry(kcs_bmc, &kcs_bmc_devices, entry) {
>+		rc = cdev->ops->add_device(kcs_bmc);
>+		if (rc)
>+			dev_err(kcs_bmc->dev, "Failed to add chardev for KCS channel %d: %d",
>+				kcs_bmc->channel, rc);
>+	}
>+	mutex_unlock(&kcs_bmc_lock);
>+
>+	return 0;

...return value again here...

>+}
>+EXPORT_SYMBOL(kcs_bmc_register_cdev);
>+
>+int kcs_bmc_unregister_cdev(struct kcs_bmc_cdev *cdev)
>+{
>+	struct kcs_bmc_device *kcs_bmc;
>+	int rc;
>+
>+	mutex_lock(&kcs_bmc_lock);
>+	list_del(&cdev->entry);
>+	list_for_each_entry(kcs_bmc, &kcs_bmc_devices, entry) {
>+		rc = cdev->ops->remove_device(kcs_bmc);
>+		if (rc)
>+			dev_err(kcs_bmc->dev, "Failed to add chardev for KCS channel %d: %d",

s/add/remove/

Might also want to differentiate the *_device() error messages from the
*_cdev() ones a bit more?

>+				kcs_bmc->channel, rc);
>+	}
>+	mutex_unlock(&kcs_bmc_lock);
>+
>+	return rc;

...but this one is a bit incongruous, propagating the return value of
only the last ->remove_device() call.

(I'd have expected this to trigger a warning about returning a
potentially uninitialized 'rc', but in some manual testing it doesn't
seem to do so for me...not certain why.)

>+}
>+EXPORT_SYMBOL(kcs_bmc_unregister_cdev);
>+
> MODULE_LICENSE("GPL v2");
> MODULE_AUTHOR("Haiyue Wang <[email-masked]>");
> MODULE_AUTHOR("Andrew Jeffery <[email-masked]>");
>diff --git a/drivers/char/ipmi/kcs_bmc.h b/drivers/char/ipmi/kcs_bmc.h
>index 3f266740c759..5deb9a0b8e60 100644
>--- a/drivers/char/ipmi/kcs_bmc.h
>+++ b/drivers/char/ipmi/kcs_bmc.h
>@@ -42,8 +42,4 @@ struct kcs_bmc_device {
> 	spinlock_t lock;
> 	struct kcs_bmc_client *client;
> };
>-
>-/* Temporary exports while refactoring */
>-int kcs_bmc_ipmi_attach_cdev(struct kcs_bmc_device *kcs_bmc);
>-int kcs_bmc_ipmi_detach_cdev(struct kcs_bmc_device *kcs_bmc);
> #endif /* __KCS_BMC_H__ */
>diff --git a/drivers/char/ipmi/kcs_bmc_cdev_ipmi.c b/drivers/char/ipmi/kcs_bmc_cdev_ipmi.c
>index 58c42e76483d..df83d67851ac 100644
>--- a/drivers/char/ipmi/kcs_bmc_cdev_ipmi.c
>+++ b/drivers/char/ipmi/kcs_bmc_cdev_ipmi.c
>@@ -469,8 +469,7 @@ static const struct file_operations kcs_bmc_ipmi_fops = {
> static DEFINE_SPINLOCK(kcs_bmc_ipmi_instances_lock);
> static LIST_HEAD(kcs_bmc_ipmi_instances);
>
>-int kcs_bmc_ipmi_attach_cdev(struct kcs_bmc_device *kcs_bmc);
>-int kcs_bmc_ipmi_attach_cdev(struct kcs_bmc_device *kcs_bmc)
>+static int kcs_bmc_ipmi_attach_cdev(struct kcs_bmc_device *kcs_bmc)
> {
> 	struct kcs_bmc_ipmi *priv;
> 	int rc;
>@@ -512,10 +511,8 @@ int kcs_bmc_ipmi_attach_cdev(struct kcs_bmc_device *kcs_bmc)
>
> 	return 0;
> }
>-EXPORT_SYMBOL(kcs_bmc_ipmi_attach_cdev);
>
>-int kcs_bmc_ipmi_detach_cdev(struct kcs_bmc_device *kcs_bmc);
>-int kcs_bmc_ipmi_detach_cdev(struct kcs_bmc_device *kcs_bmc)
>+static int kcs_bmc_ipmi_detach_cdev(struct kcs_bmc_device *kcs_bmc)
> {
> 	struct kcs_bmc_ipmi *priv = NULL, *pos;
>
>@@ -541,7 +538,31 @@ int kcs_bmc_ipmi_detach_cdev(struct kcs_bmc_device *kcs_bmc)
>
> 	return 0;
> }
>-EXPORT_SYMBOL(kcs_bmc_ipmi_detach_cdev);
>+
>+static const struct kcs_bmc_cdev_ops kcs_bmc_ipmi_cdev_ops = {
>+	.add_device = kcs_bmc_ipmi_attach_cdev,
>+	.remove_device = kcs_bmc_ipmi_detach_cdev,
>+};
>+
>+static struct kcs_bmc_cdev kcs_bmc_ipmi_cdev = {
>+	.ops = &kcs_bmc_ipmi_cdev_ops,
>+};
>+
>+static int kcs_bmc_ipmi_init(void)
>+{
>+	return kcs_bmc_register_cdev(&kcs_bmc_ipmi_cdev);
>+}
>+module_init(kcs_bmc_ipmi_init);
>+
>+static void kcs_bmc_ipmi_exit(void)
>+{
>+	int rc;
>+
>+	rc = kcs_bmc_unregister_cdev(&kcs_bmc_ipmi_cdev);
>+	if (rc)
>+		pr_warn("Failed to remove KCS BMC client: %d", rc);
>+}
>+module_exit(kcs_bmc_ipmi_exit);
>
> MODULE_LICENSE("GPL v2");
> MODULE_AUTHOR("Haiyue Wang <[email-masked]>");
>diff --git a/drivers/char/ipmi/kcs_bmc_client.h b/drivers/char/ipmi/kcs_bmc_client.h
>index 2dd710f4b4aa..d0a7404ff584 100644
>--- a/drivers/char/ipmi/kcs_bmc_client.h
>+++ b/drivers/char/ipmi/kcs_bmc_client.h
>@@ -10,6 +10,17 @@
>
> #include "kcs_bmc.h"
>
>+struct kcs_bmc_cdev_ops {
>+	int (*add_device)(struct kcs_bmc_device *kcs_bmc);
>+	int (*remove_device)(struct kcs_bmc_device *kcs_bmc);
>+};
>+
>+struct kcs_bmc_cdev {
>+	struct list_head entry;
>+
>+	const struct kcs_bmc_cdev_ops *ops;
>+};
>+
> struct kcs_bmc_client_ops {
> 	int (*event)(struct kcs_bmc_client *client);
> };
>@@ -20,6 +31,9 @@ struct kcs_bmc_client {
> 	struct kcs_bmc_device *dev;
> };
>
>+int kcs_bmc_register_cdev(struct kcs_bmc_cdev *cdev);
>+int kcs_bmc_unregister_cdev(struct kcs_bmc_cdev *cdev);
>+
> int kcs_bmc_enable_device(struct kcs_bmc_device *kcs_bmc, struct kcs_bmc_client *client);
> void kcs_bmc_disable_device(struct kcs_bmc_device *kcs_bmc, struct kcs_bmc_client *client);
>
>-- 
>2.27.0
>
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