linux-kernel - [PATCH v2] ipmi: looped device detection

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Message-Id: <20180911225630.124502-1-venture@google.com>
Date:   Tue, 11 Sep 2018 15:56:30 -0700
From:   Patrick Venture <venture@...gle.com>
To:     venture@...gle.com, minyard@....org, arnd@...db.de,
        gregkh@...uxfoundation.org
Cc:     openipmi-developer@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, openbmc@...ts.ozlabs.org
Subject: [PATCH v2] ipmi: looped device detection

Try to get the device ID repeatedly during initialization before giving up.
The BMC isn't always responsive, and this allows it to be slightly flaky
during early boot.

Tested: Installed on a system with the BMC software disabled
such that it was non-responsive.  The driver correctly detected this
and gave up as expected.  Then I re-enabled the BMC software unloaded
and reloaded the driver and it was detected properly.

Signed-off-by: Patrick Venture <venture@...gle.com>
---
v2:
 - removed extra variable that was set but not used.
---
 drivers/char/ipmi/ipmi_si_intf.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/char/ipmi/ipmi_si_intf.c b/drivers/char/ipmi/ipmi_si_intf.c
index 90ec010bffbd..5fed96897fe8 100644
--- a/drivers/char/ipmi/ipmi_si_intf.c
+++ b/drivers/char/ipmi/ipmi_si_intf.c
@@ -1918,11 +1918,13 @@ int ipmi_si_add_smi(struct si_sm_io *io)
  * held, primarily to keep smi_num consistent, we only one to do these
  * one at a time.
  */
+#define GET_DEVICE_ID_ATTEMPTS	5
 static int try_smi_init(struct smi_info *new_smi)
 {
 	int rv = 0;
 	int i;
 	char *init_name = NULL;
+	unsigned long sleep_rm;
 
 	pr_info(PFX "Trying %s-specified %s state machine at %s address 0x%lx, slave address 0x%x, irq %d\n",
 		ipmi_addr_src_to_str(new_smi->io.addr_source),
@@ -2003,7 +2005,26 @@ static int try_smi_init(struct smi_info *new_smi)
 	 * Attempt a get device id command.  If it fails, we probably
 	 * don't have a BMC here.
 	 */
-	rv = try_get_dev_id(new_smi);
+	for (i = 0; i < GET_DEVICE_ID_ATTEMPTS; i++) {
+		pr_info(PFX "Attempting to read BMC device ID\n");
+		rv = try_get_dev_id(new_smi);
+		/* If it succeeded, stop trying */
+		if (!rv)
+			break;
+
+		/* Sleep for ~0.25s before trying again instead of hammering
+		 * the BMC.
+		 */
+		sleep_rm = msleep_interruptible(250);
+		if (sleep_rm != 0) {
+			pr_info(PFX "Find BMC interrupted\n");
+			rv = -EINTR;
+			goto out_err;
+		}
+	}
+
+	/* If we exited the loop above and rv is non-zero we ran out of tries.
+	 */
 	if (rv) {
 		if (new_smi->io.addr_source)
 			dev_err(new_smi->io.dev,
-- 
2.19.0.rc2.392.g5ba43deb5a-goog