drivers/smmstore: Retry APM SCI if it fails

For some reason, the APM SCI to install the SMMSTORE comm buffer
regularly, but not always, fails with 0x4ed on ADL. In this case, a
second attempt seems to always complete successfully.

Tested on system76/darp8 and system76/galp6.

Change-Id: I843116113b8c24f1aee42f9d9042cdc0471a1b43
Signed-off-by: Tim Crawford <[email protected]>

Author: crawfxrd

src/drivers/smmstore/ramstage.c

@@ -57,18 +57,22 @@ static void init_store(void *unused)
 
 	printk(BIOS_INFO, "SMMSTORE: Setting up SMI handler\n");
 
-	/* Issue SMI using APM to update the com buffer and to lock the SMMSTORE */
-	__asm__ __volatile__ (
-		"outb %%al, %%dx"
-		: "=a" (eax)
-		: "a" ((SMMSTORE_CMD_INIT << 8) | APM_CNT_SMMSTORE),
-		  "b" (ebx),
-		  "d" (APM_CNT)
-		: "memory");
+	for (int retries = 0; retries < 3; retries++) {
+		/* Issue SMI using APM to update the com buffer and to lock the SMMSTORE */
+		__asm__ __volatile__ (
+			"outb %%al, %%dx"
+			: "=a" (eax)
+			: "a" ((SMMSTORE_CMD_INIT << 8) | APM_CNT_SMMSTORE),
+			  "b" (ebx),
+			  "d" (APM_CNT)
+			: "memory");
 
-	if (eax != SMMSTORE_RET_SUCCESS) {
-		printk(BIOS_ERR, "SMMSTORE: Failed to install com buffer\n");
-		return;
+		if (eax == SMMSTORE_RET_SUCCESS) {
+			printk(BIOS_INFO, "SMMSTORE: Installed com buffer\n");
+			break;
+		}
+
+		printk(BIOS_ERR, "SMMSTORE: Failed to install com buffer: 0x%x\n", eax);
 	}
 }