google/trogdor: Add backlight support for Parade ps8640

Add backlight support in ps8640 through the AUX channel using eDP
DPCD registers.

BUG=b:202966352
BRANCH=trogdor
TEST=verified firmware screen works on homestar rev4

Change-Id: Ief1bf56c89c8215427dcbddfc67e8bcd4c3607d2
Signed-off-by: xuxinxiong <xuxinxiong@huaqin.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/58624
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/lib/dp_aux.c

@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <delay.h>
+#include <dp_aux.h>
+#include <console/console.h>
+#include <timer.h>
+
+bool dp_aux_request_is_write(enum aux_request request)
+{
+	switch (request) {
+	case I2C_RAW_WRITE_AND_STOP:
+	case I2C_RAW_WRITE:
+	case DPCD_WRITE:
+		return true;
+	default:
+		return false;
+	}
+}
+
+enum i2c_over_aux dp_get_aux_cmd(enum aux_request request, uint32_t remaining_after_this)
+{
+	switch (request) {
+	case I2C_RAW_WRITE_AND_STOP:
+		if (!remaining_after_this)
+			return I2C_OVER_AUX_WRITE_MOT_0;
+		/* fallthrough */
+	case I2C_RAW_WRITE:
+		return I2C_OVER_AUX_WRITE_MOT_1;
+	case I2C_RAW_READ_AND_STOP:
+		if (!remaining_after_this)
+			return I2C_OVER_AUX_READ_MOT_0;
+		/* fallthrough */
+	case I2C_RAW_READ:
+		return I2C_OVER_AUX_READ_MOT_1;
+	case DPCD_WRITE:
+		return NATIVE_AUX_WRITE;
+	case DPCD_READ:
+	default:
+		return NATIVE_AUX_READ;
+	}
+}