[PATCH] ACPI / EC: Fix a boot EC regresion by restoring boot EC support for the DSDT EC

[Lv Zheng <lv.zheng@intel.com>]

According to the Windows probing result, during the table loading, ECDT EC
should be used. And the ECDT EC is also effective during the period the
namespace objects are initialized (we can see a separate process executing
_STA/_INI on Windows before executing other device specific control
methods). During the device enumration, the EC device described in DSDT
should be used. But there are differences between Linux and Windows around
the device probing order. Thus in Linux, we should enable early EC accesses
in order not to trigger issues by the device enumeration order difference.

This patch thus converts acpi_boot_ec_enable() into acpi_ec_dsdt_probe() to
fix the gap. This also fixes a regression reported by the real Linux users
after we switched table loading/ECDT support to be ACPI spec 2.0 compliant.

Fixes: 59f0aa9480cf ("ACPI 2.0 / ECDT: Remove early namespace reference from EC")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=119261
Reported-and-tested-by: Gabriele Mazzotta <mzt@gmail.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
---
Index: linux-acpica/drivers/acpi/ec.c
===================================================================
--- linux-acpica.orig/drivers/acpi/ec.c
+++ linux-acpica/drivers/acpi/ec.c
@@ -1446,10 +1446,30 @@ ec_parse_io_ports(struct acpi_resource *
 	return AE_OK;
 }
 
-int __init acpi_boot_ec_enable(void)
+static const struct acpi_device_id ec_device_ids[] = {
+	{"PNP0C09", 0},
+	{"", 0},
+};
+
+int __init acpi_ec_dsdt_probe(void)
 {
-	if (!boot_ec)
+	acpi_status status;
+
+	if (boot_ec)
 		return 0;
+
+	/*
+	 * Finding EC from DSDT if there is no ECDT EC available. When this
+	 * function is invoked, ACPI tables have been fully loaded, we can
+	 * walk namespace now.
+	 */
+	boot_ec = make_acpi_ec();
+	if (!boot_ec)
+		return -ENOMEM;
+	status = acpi_get_devices(ec_device_ids[0].id,
+				  ec_parse_device, boot_ec, NULL);
+	if (ACPI_FAILURE(status) || !boot_ec->handle)
+		return -ENODEV;
 	if (!ec_install_handlers(boot_ec)) {
 		first_ec = boot_ec;
 		return 0;
@@ -1457,11 +1477,6 @@ int __init acpi_boot_ec_enable(void)
 	return -EFAULT;
 }
 
-static const struct acpi_device_id ec_device_ids[] = {
-	{"PNP0C09", 0},
-	{"", 0},
-};
-
 #if 0
 /*
  * Some EC firmware variations refuses to respond QR_EC when SCI_EVT is not
Index: linux-acpica/drivers/acpi/bus.c
===================================================================
--- linux-acpica.orig/drivers/acpi/bus.c
+++ linux-acpica/drivers/acpi/bus.c
@@ -1053,7 +1053,7 @@ static int __init acpi_bus_init(void)
 	 * Maybe EC region is required at bus_scan/acpi_get_devices. So it
 	 * is necessary to enable it as early as possible.
 	 */
-	acpi_boot_ec_enable();
+	acpi_ec_dsdt_probe();
 
 	printk(KERN_INFO PREFIX "Interpreter enabled\n");
 
Index: linux-acpica/drivers/acpi/internal.h
===================================================================
--- linux-acpica.orig/drivers/acpi/internal.h
+++ linux-acpica/drivers/acpi/internal.h
@@ -181,7 +181,7 @@ typedef int (*acpi_ec_query_func) (void 
 
 int acpi_ec_init(void);
 int acpi_ec_ecdt_probe(void);
-int acpi_boot_ec_enable(void);
+int acpi_ec_dsdt_probe(void);
 void acpi_ec_block_transactions(void);
 void acpi_ec_unblock_transactions(void);
 void acpi_ec_unblock_transactions_early(void);