From: Arthur Heymans <arthur@aheymans.xyz>
Date: Mon, 18 Nov 2019 10:19:31 +0000 (+0100)
Subject: firmware: google: Probe for a GSMI handler in firmware
X-Git-Tag: block-5.6-2020-02-05~28^2~15
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=e4924ee263b015cc2e397ca871d870925e2673b4;p=linux-2.6-block.git

firmware: google: Probe for a GSMI handler in firmware

Currently this driver is loaded if the DMI string matches coreboot
and has a proper smi_command in the ACPI FADT table, but a GSMI handler in
SMM is an optional feature in coreboot.

So probe for a SMM GSMI handler before initializing the driver.
If the smihandler leaves the calling argument in %eax in the SMM save state
untouched that generally means the is no handler for GSMI.

Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Link: https://lore.kernel.org/r/20191118101934.22526-4-patrick.rudolph@9elements.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/firmware/google/gsmi.c b/drivers/firmware/google/gsmi.c
index 974c769b75cf..5b2011ebbe26 100644
--- a/drivers/firmware/google/gsmi.c
+++ b/drivers/firmware/google/gsmi.c
@@ -76,6 +76,7 @@
 #define GSMI_CMD_LOG_S0IX_RESUME	0x0b
 #define GSMI_CMD_CLEAR_CONFIG		0x20
 #define GSMI_CMD_HANDSHAKE_TYPE		0xC1
+#define GSMI_CMD_RESERVED		0xff
 
 /* Magic entry type for kernel events */
 #define GSMI_LOG_ENTRY_TYPE_KERNEL     0xDEAD
@@ -746,6 +747,7 @@ MODULE_DEVICE_TABLE(dmi, gsmi_dmi_table);
 static __init int gsmi_system_valid(void)
 {
 	u32 hash;
+	u16 cmd, result;
 
 	if (!dmi_check_system(gsmi_dmi_table))
 		return -ENODEV;
@@ -780,6 +782,23 @@ static __init int gsmi_system_valid(void)
 		return -ENODEV;
 	}
 
+	/* Test the smihandler with a bogus command. If it leaves the
+	 * calling argument in %ax untouched, there is no handler for
+	 * GSMI commands.
+	 */
+	cmd = GSMI_CALLBACK | GSMI_CMD_RESERVED << 8;
+	asm volatile (
+		"outb %%al, %%dx\n\t"
+		: "=a" (result)
+		: "0" (cmd),
+		  "d" (acpi_gbl_FADT.smi_command)
+		: "memory", "cc"
+		);
+	if (cmd == result) {
+		pr_info("gsmi: no gsmi handler in firmware\n");
+		return -ENODEV;
+	}
+
 	/* Found */
 	return 0;
 }