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firmware: google: Probe for a GSMI handler in firmware

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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>
This commit is contained in:
Arthur Heymans 2019-11-18 11:19:31 +01:00 committed by Greg Kroah-Hartman
parent c6e7af0515
commit e4924ee263
1 changed files with 19 additions and 0 deletions
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19
drivers/firmware/google/gsmi.c
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@ -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;
}