[PATCH 05/13] platform/apple-gmux: Write switch state to EFI on MMIO devices

[Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>]

From: Andre Eikmeyer <dev@deq.rocks>

On T2 devices (MMIO), the T2 coprocessor reads gpu-active efi
variable, and macOS seems to write it, so to properly communciate
to the T2 coprocessor, we write gpu-active.

Co-developed: Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>
Signed-off-by: Atharva Tiwari <atharvatiwarilinuxdev@gmail.com>

Signed-off-by: Andre Eikmeyer <dev@deq.rocks>
---
 drivers/platform/x86/Kconfig      |  1 +
 drivers/platform/x86/apple-gmux.c | 29 +++++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index c37e76066..01895d511 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -217,6 +217,7 @@ config APPLE_GMUX
 	depends on ACPI && PCI
 	depends on PNP
 	depends on BACKLIGHT_CLASS_DEVICE
+	depends on EFI
 	help
 	  This driver provides support for the gmux device found on many
 	  Apple laptops, which controls the display mux for the hybrid
diff --git a/drivers/platform/x86/apple-gmux.c b/drivers/platform/x86/apple-gmux.c
index bef87a57a..637b3b216 100644
--- a/drivers/platform/x86/apple-gmux.c
+++ b/drivers/platform/x86/apple-gmux.c
@@ -27,6 +27,7 @@
 #include <linux/dmi.h>
 #include <linux/workqueue.h>
 #include <linux/pm_runtime.h>
+#include <linux/efi.h>
 #include <acpi/video.h>
 #include <asm/io.h>
 
@@ -494,6 +495,31 @@ static void gmux_write_switch_state(struct apple_gmux_data *gmux_data)
 		gmux_write8(gmux_data, GMUX_PORT_SWITCH_EXTERNAL, 3);
 }
 
+#define APPLE_GPU_VARS_GUID EFI_GUID(0xfa4ce28d, 0xb62f, 0x4c99, \
+				     0x9c, 0xc3, 0x68, 0x15, 0x68, 0x6e, 0x30, 0xf9)
+
+static efi_char16_t gmux_gpu_active_name[] = L"gpu-active";
+
+static void gmux_write_switch_state_efi(struct apple_gmux_data *gmux_data)
+{
+	efi_guid_t guid = APPLE_GPU_VARS_GUID;
+	u32 active = gmux_data->switch_state_display == VGA_SWITCHEROO_IGD;
+	efi_status_t status;
+
+	if (!efivar_is_available())
+		return;
+
+	status = efivar_set_variable(gmux_gpu_active_name, &guid,
+				     EFI_VARIABLE_NON_VOLATILE |
+				     EFI_VARIABLE_BOOTSERVICE_ACCESS |
+				     EFI_VARIABLE_RUNTIME_ACCESS,
+				     sizeof(active), &active);
+	if (status != EFI_SUCCESS)
+		pr_warn("writing gpu-active failed: 0x%lx\n", status);
+	else
+		pr_debug("gpu-active: %u\n", active);
+}
+
 static int gmux_switchto(enum vga_switcheroo_client_id id)
 {
 	apple_gmux_data->switch_state_ddc = id;
@@ -502,6 +528,8 @@ static int gmux_switchto(enum vga_switcheroo_client_id id)
 		apple_gmux_data->switch_state_external = id;
 
 	gmux_write_switch_state(apple_gmux_data);
+	if (apple_gmux_data->type == APPLE_GMUX_TYPE_MMIO)
+		gmux_write_switch_state_efi(apple_gmux_data);
 
 	return 0;
 }
@@ -1283,3 +1311,4 @@ MODULE_AUTHOR("Seth Forshee <seth.forshee@canonical.com>");
 MODULE_DESCRIPTION("Apple Gmux Driver");
 MODULE_LICENSE("GPL");
 MODULE_DEVICE_TABLE(pnp, gmux_device_ids);
+MODULE_IMPORT_NS("EFIVAR");
-- 
2.55.0