soc/amd/common: add rudimentary ATIF support

The Linux kenerl driver for AMD gpu currently has a floor
value of 12 for brightness settings (AMDGPU_DM_DEFAULT_MIN_BACKLIGHT).
AMD indicates they did this because they were concerned with certain
panels flickering at lower backlight values. However, for unaffected
panels it's desirable to be able to have the panel "turn off" at
the lowest backlight setting. The only way to do that is to provide
ATIF bindings that indicate backlight range.

Option SOC_AMD_COMMON_BLOCK_GRAPHICS_ATIF is added to provide a full
range for the backlight setting. If needed, this path can be built upon
for fuller support, but for the time being this is the only thing
necessary to make the backlight be full range.

BUG=b:163583825

Change-Id: If76801a8daf6a5e56ba7d118956f3ebce74e567a
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44642
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

2 files changed, 109 insertions, 0 deletions

diff --git a/src/soc/amd/common/block/graphics/Kconfig b/src/soc/amd/common/block/graphics/Kconfig
index 8aa2a20a3caa..4cda353c5f2c 100644
--- a/src/soc/amd/common/block/graphics/Kconfig
+++ b/src/soc/amd/common/block/graphics/Kconfig
@@ -3,3 +3,11 @@ config SOC_AMD_COMMON_BLOCK_GRAPHICS
 	default n
 	help
 	  Select this option to use AMD common graphics driver support.
+
+config SOC_AMD_COMMON_BLOCK_GRAPHICS_ATIF
+	bool
+	depends on SOC_AMD_COMMON_BLOCK_GRAPHICS
+	help
+	  Select this option to provide ATIF method with display brightness querying.
+	  Currently, the exported values only open up 0-255 as the brightness range for
+	  the display.
diff --git a/src/soc/amd/common/block/graphics/graphics.c b/src/soc/amd/common/block/graphics/graphics.c
index 466a91c6667e..24cabfe454b5 100644
--- a/src/soc/amd/common/block/graphics/graphics.c
+++ b/src/soc/amd/common/block/graphics/graphics.c
@@ -1,13 +1,114 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include <acpi/acpi_device.h>
+#include <acpi/acpigen.h>
 #include <device/pci.h>
 #include <device/pci_ids.h>
 
+#define ATIF_FUNCTION_VERIFY_INTERFACE 0x0
+struct atif_verify_interface_output {
+	uint16_t size; /* Size of this object, including size field */
+	uint16_t version;
+	uint32_t supported_notifications;
+	uint32_t supported_functions; /* Bit n set if function n+1 supported. */
+};
+
+#define ATIF_FUNCTION_QUERY_BRIGHTNESS_TRANSFER_CHARACTERISTICS    0x10
+# define ATIF_QBTC_REQUEST_LCD1                              0
+/* error codes */
+# define ATIF_QBTC_ERROR_CODE_SUCCESS                        0
+# define ATIF_QBTC_ERROR_CODE_FAILURE                        1
+# define ATIF_QBTC_ERROR_CODE_DEVICE_NOT_SUPPORTED           2
+struct atif_brightness_input {
+	uint16_t size;
+	/* ATIF doc indicates this field is a word, but the kernel drivers uses a byte. */
+	uint8_t requested_display;
+};
+struct atif_brightness_output {
+	uint16_t size; /* Size of this object, including size field. */
+	uint16_t flags; /* Currently all reserved. */
+	uint8_t error_code;
+	/* default brightness fields currently ignored by Linux driver. */
+	uint8_t default_brightness_ac; /* Percentage brightness when connected to AC. */
+	uint8_t default_brightness_dc; /* Percentage brightness when connected to DC. */
+	/* The following 2 fields are the only ones honored by Linux driver currently. */
+	uint8_t min_input_signal_level; /* 0-255 corresponding to 0% */
+	uint8_t max_input_signal_level; /* 0-255 corresponding to 100% */
+	/* Array of data points consisting of:
+	 *  { uint8_t luminance_level; (percent)
+	 *    uint8_t input_signal_level; (0-255 in value) }
+	 * Linux ignores these fields so no support currently. */
+	uint8_t count_data_points; /* Count of data points. */
+};
+
+static void generate_atif(const struct device *dev)
+{
+	struct atif_verify_interface_output verify_output = {
+		.size = sizeof(verify_output),
+		.version = 1,
+		.supported_functions =
+			BIT(ATIF_FUNCTION_QUERY_BRIGHTNESS_TRANSFER_CHARACTERISTICS - 1),
+	};
+	struct atif_brightness_output brightness_error = {
+		.size = sizeof(brightness_error),
+		.error_code = ATIF_QBTC_ERROR_CODE_DEVICE_NOT_SUPPORTED,
+	};
+	struct atif_brightness_output brightness_out = {
+		.size = sizeof(brightness_out),
+		.error_code = ATIF_QBTC_ERROR_CODE_SUCCESS,
+		.min_input_signal_level = 0,
+		.max_input_signal_level = 255,
+	};
+
+	/* Scope (\_SB.PCI0.PBRA.IGFX) */
+	acpigen_write_scope(acpi_device_path(dev));
+	/* Method (ATIF, 2, NotSerialized) */
+	acpigen_write_method("ATIF", 2);
+	/* ToInteger (Arg0, Local0) */
+	acpigen_write_to_integer(ARG0_OP, LOCAL0_OP);
+
+	/* If ((Local0 == Zero)) */
+	acpigen_write_if_lequal_op_int(LOCAL0_OP, ATIF_FUNCTION_VERIFY_INTERFACE);
+	/* Return (Buffer (0x0C) { ... } */
+	acpigen_write_return_byte_buffer((uint8_t *)(void *)&verify_output,
+		sizeof(verify_output));
+	acpigen_pop_len(); /* if (LEqual(Local0, 0) */
+
+	/* ElseIf ((Local0 == 0x10)) */
+	acpigen_write_else();
+	acpigen_write_if_lequal_op_int(LOCAL0_OP,
+		ATIF_FUNCTION_QUERY_BRIGHTNESS_TRANSFER_CHARACTERISTICS);
+	/* CreateByteField (Arg1, 0x02, DISP) */
+	acpigen_write_create_byte_field(ARG1_OP,
+		offsetof(struct atif_brightness_input, requested_display), "DISP");
+	/* ToInteger (DISP, Local1) */
+	acpigen_write_to_integer_from_namestring("DISP", LOCAL1_OP);
+	/* If ((Local1 == Zero)) */
+	acpigen_write_if_lequal_op_int(LOCAL1_OP, ATIF_QBTC_REQUEST_LCD1);
+	/* Return (Buffer (0x0A) { ... } */
+	acpigen_write_return_byte_buffer((uint8_t *)(void *)&brightness_out,
+		sizeof(brightness_out));
+	acpigen_pop_len(); /* if (LEqual(Local2, ATIF_QBTC_REQUEST_LCD1) */
+	/* Else */
+	acpigen_write_else();
+	/* Return (Buffer (0x0A) */
+	acpigen_write_return_byte_buffer((uint8_t *)(void *)&brightness_error,
+		sizeof(brightness_error));
+	acpigen_pop_len(); /* else */
+
+	acpigen_pop_len(); /* if (LEqual(Local0, 0x10) */
+	acpigen_pop_len(); /* else */
+
+	acpigen_pop_len(); /* Method */
+	acpigen_pop_len(); /* Scope */
+}
+
 static void graphics_fill_ssdt(const struct device *dev)
 {
 	acpi_device_write_pci_dev(dev);
 	pci_rom_ssdt(dev);
+	if (CONFIG(SOC_AMD_COMMON_BLOCK_GRAPHICS_ATIF))
+		generate_atif(dev);
 }
 
 static const char *graphics_acpi_name(const struct device *dev)