[PATCH] i2c: i2c-scmi: add a MS HID

[Viktor Krasnov <vkrasnov@dev.rtsoft.ru>]

From: Edgar Cherkasov <echerkasov@dev.rtsoft.ru>

Description of the problem:
 - i2c-scmi driver contains only two identifiers "SMBUS01" and "SMBUSIBM";
 - the fist HID (SMBUS01) is clearly defined in "SMBus Control Method
   Interface Specification, version 1.0": "Each device must specify 
   'SMBUS01' as its _HID and use a unique _UID value";
 - unfortunately, BIOS vendors (like AMI) seem to ignore this requirement
   and implement "SMB0001" HID instead of "SMBUS01";
 - I speculate that they do this because only "SMB0001" is hard coded in
   Windows SMBus driver produced by Microsoft.

This leads to following situation:
 - SMBus works out of box in Windows but not in Linux;
 - board vendors are forced to add correct "SMBUS01" HID to BIOS to make
   SMBus work in Linux. Moreover the same board vendors complain that
   tools (3-rd party ASL compiler) do not like the "SMBUS01" identifier
   and produce errors.  So they need to constantly patch the compiler for 
   each new version of BIOS.

As it is very unlikely that BIOS vendors implement a correct HID in
future, I would propose to consider whether it is possible to work around
the problem by adding MS HID to the Linux i2c-scmi driver.

Signed-off-by: Edgar Cherkasov <echerkasov@dev.rtsoft.ru>
Signed-off-by: Michael Brunner <Michael.Brunner@kontron.com>
Acked-by: Viktor Krasnov <vkrasnov@dev.rtsoft.ru>
---
 drivers/i2c/busses/i2c-scmi.c | 1 +
 include/acpi/acpi_drivers.h   | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/drivers/i2c/busses/i2c-scmi.c b/drivers/i2c/busses/i2c-scmi.c
index dfc98df..fb9aee0 100644
--- a/drivers/i2c/busses/i2c-scmi.c
+++ b/drivers/i2c/busses/i2c-scmi.c
@@ -51,6 +51,7 @@ struct acpi_smbus_cmi {
 static const struct acpi_device_id acpi_smbus_cmi_ids[] = {
 	{"SMBUS01", (kernel_ulong_t)&smbus_methods},
 	{ACPI_SMBUS_IBM_HID, (kernel_ulong_t)&ibm_smbus_methods},
+	{ACPI_SMBUS_MS_HID, (kernel_ulong_t)&smbus_methods},
 	{"", 0}
 };
 MODULE_DEVICE_TABLE(acpi, acpi_smbus_cmi_ids);
diff --git a/include/acpi/acpi_drivers.h b/include/acpi/acpi_drivers.h
index 29c6912..d34538b 100644
--- a/include/acpi/acpi_drivers.h
+++ b/include/acpi/acpi_drivers.h
@@ -60,6 +60,8 @@
 #define ACPI_DOCK_HID			"LNXDOCK"
 /* Quirk for broken IBM BIOSes */
 #define ACPI_SMBUS_IBM_HID		"SMBUSIBM"
+/* SMBUS HID definition as supported by Microsoft Windows */
+#define ACPI_SMBUS_MS_HID		"SMB0001"
 
 /*
  * For fixed hardware buttons, we fabricate acpi_devices with HID
-- 
1.9.3