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From: Stuart Hayes <>
Date: Wed, 2 Mar 2011 12:42:05 +0000 (+0100)
Subject: dcdbas: force SMI to happen when expected

dcdbas: force SMI to happen when expected

The dcdbas driver can do an I/O write to cause a SMI to occur.  The SMI handler
looks at certain registers and memory locations, so the SMI needs to happen
immediately.  On some systems I/O writes are posted, though, causing the SMI to
happen well after the "outb" occurred, which causes random failures.  Following
the "outb" with an "inb" forces the write to go through even if it is posted.

Signed-off-by: Stuart Hayes <>
Acked-by: Doug Warzecha <>
Signed-off-by: Jiri Kosina <>

diff --git a/drivers/firmware/dcdbas.c b/drivers/firmware/dcdbas.c
index 69ad529..ea5ac2d 100644
--- a/drivers/firmware/dcdbas.c
+++ b/drivers/firmware/dcdbas.c
@@ -268,8 +268,10 @@ int dcdbas_smi_request(struct smi_cmd *smi_cmd)
 	/* generate SMI */
+	/* inb to force posted write through and make SMI happen now */
 	asm volatile (
-		"outb %b0,%w1"
+		"outb %b0,%w1\n"
+		"inb %w1"
 		: /* no output args */
 		: "a" (smi_cmd->command_code),
 		  "d" (smi_cmd->command_address),