linux-kernel - [PATCH] ipmi: retry to get device id when error

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Date:   Sun, 13 Sep 2020 20:02:03 +0800
From:   Xianting Tian <tian.xianting@....com>
To:     <minyard@....org>, <arnd@...db.de>, <gregkh@...uxfoundation.org>
CC:     <openipmi-developer@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>,
        Xianting Tian <tian.xianting@....com>
Subject: [PATCH] ipmi: retry to get device id when error

We can't get bmc's device id with low probability when loading ipmi driver,
it caused bmc device register failed. This issue may caused by bad lpc
signal quality. When this issue happened, we got below kernel printks:
	[Wed Sep  9 19:52:03 2020] ipmi_si IPI0001:00: IPMI message handler: device id demangle failed: -22
	[Wed Sep  9 19:52:03 2020] IPMI BT: using default values
	[Wed Sep  9 19:52:03 2020] IPMI BT: req2rsp=5 secs retries=2
	[Wed Sep  9 19:52:03 2020] ipmi_si IPI0001:00: Unable to get the device id: -5
	[Wed Sep  9 19:52:04 2020] ipmi_si IPI0001:00: Unable to register device: error -5

When this issue happened, we want to manually unload the driver and try to
load it again, but it can't be unloaded by 'rmmod' as it is already 'in use'.

We add below 'printk' in handle_one_recv_msg(), when this issue happened,
the msg we received is "Recv: 1c 01 d5", which means the data_len is 1,
data[0] is 0xd5.
	Debug code:
	static int handle_one_recv_msg(struct ipmi_smi *intf,
                               struct ipmi_smi_msg *msg) {
        	printk("Recv: %*ph\n", msg->rsp_size, msg->rsp);
		... ...
	}
Then in ipmi_demangle_device_id(), it returned '-EINVAL' as 'data_len < 7'
and 'data[0] != 0'.

We used this patch to retry to get device id when error happen, we
reproduced this issue again and the retry succeed on the first retry, we
finally got the correct msg and then all is ok:
Recv: 1c 01 00 01 81 05 84 02 af db 07 00 01 00 b9 00 10 00

So use retry machanism in this patch to give bmc more opportunity to
correctly response kernel.

Signed-off-by: Xianting Tian <tian.xianting@....com>
---
 drivers/char/ipmi/ipmi_msghandler.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
index 737c0b6b2..bfb2de77a 100644
--- a/drivers/char/ipmi/ipmi_msghandler.c
+++ b/drivers/char/ipmi/ipmi_msghandler.c
@@ -34,6 +34,7 @@
 #include <linux/uuid.h>
 #include <linux/nospec.h>
 #include <linux/vmalloc.h>
+#include <linux/delay.h>
 
 #define IPMI_DRIVER_VERSION "39.2"
 
@@ -60,6 +61,9 @@ enum ipmi_panic_event_op {
 #else
 #define IPMI_PANIC_DEFAULT IPMI_SEND_PANIC_EVENT_NONE
 #endif
+
+#define GET_DEVICE_ID_MAX_RETRY	5
+
 static enum ipmi_panic_event_op ipmi_send_panic_event = IPMI_PANIC_DEFAULT;
 
 static int panic_op_write_handler(const char *val,
@@ -2426,19 +2430,26 @@ send_get_device_id_cmd(struct ipmi_smi *intf)
 static int __get_device_id(struct ipmi_smi *intf, struct bmc_device *bmc)
 {
 	int rv;
-
-	bmc->dyn_id_set = 2;
+	unsigned int retry_count = 0;
 
 	intf->null_user_handler = bmc_device_id_handler;
 
+retry:
+	bmc->dyn_id_set = 2;
+
 	rv = send_get_device_id_cmd(intf);
 	if (rv)
 		return rv;
 
 	wait_event(intf->waitq, bmc->dyn_id_set != 2);
 
-	if (!bmc->dyn_id_set)
+	if (!bmc->dyn_id_set) {
+		msleep(1000);
+		if (++retry_count <= GET_DEVICE_ID_MAX_RETRY)
+			goto retry;
+
 		rv = -EIO; /* Something went wrong in the fetch. */
+	}
 
 	/* dyn_id_set makes the id data available. */
 	smp_rmb();
-- 
2.17.1