soc/intel/cmn/gfx: Add API to report presence of external display

This patch implements an API to report the presence of an external
display on Intel silicon. The API uses information from the transcoder
and framebuffer to determine if an external display is connected.

For example, if the transcoder is attached to any DDI ports other than
DDI-A (eDP), and the framebuffer is initialized, then it is likely
that an external display is present.

This information can be used by payloads to determine whether or not
to power on the display, even if eDP is not initialized.

BUG=b:299137940
TEST=Build and boot google/rex

Scenarios:

Booting with eDP alone: has_external_display value is 0
Booting with eDP + HDMI: has_external_display value is 0
Booting with HDMI alone: has_external_display value is 1
Booting with USB-C display alone: has_external_display value is 1

Change-Id: I77436940978c7fa9368d79394b46a5e794c32e42
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78080
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
Reviewed-by: Eric Lai <ericllai@google.com>

1 files changed, 50 insertions, 0 deletions

diff --git a/src/soc/intel/common/block/graphics/graphics.c b/src/soc/intel/common/block/graphics/graphics.c
index 69754fdc93..5b2484a45f 100644
--- a/src/soc/intel/common/block/graphics/graphics.c
+++ b/src/soc/intel/common/block/graphics/graphics.c
@@ -31,6 +31,56 @@ intel_igd_get_controller_info(const struct device *device)
 	return NULL;
 }
 
+/*
+ * Transcoders contain the timing generators for eDP, DP, and HDMI interfaces.
+ * Intel transcoders are based on Quick Sync Video, which offloads video
+ * encoding and decoding tasks from the CPU to the GPU.
+ *
+ * On Intel silicon, there are four display pipes (DDI-A to DDI-D) that support
+ * blending, color adjustments, scaling, and dithering.
+ *
+ * From the display block diagram perspective, the front end of the display
+ * contains the pipes. The pipes connect to the transcoder. The transcoder
+ * (except for wireless) connects to the DDIs to drive the IO/PHY.
+ *
+ * This logic checks if the DDI-A port is attached to the transcoder and
+ * enabled (bit 27). Traditionally, the on-board display (eDP) is attached to DDI-A.
+ * If the above conditions is met, then the on-board display is present and enabled.
+ *
+ * On platforms without an on-board display (i.e., value at bits 27-30 is between 2-9),
+ * meaning that DDI-A (eDP) is not enabled.
+ *
+ * Additionally, if bits 27-30 are all set to 0, this means that no DDI ports
+ * are enabled, and there is no display.
+ *
+ * Consider external display is present and enabled, if eDP/DDI-A is not enabled
+ * and transcoder is attached to any DDI port (bits 27-30 are not zero).
+ */
+static int get_external_display_status(void)
+{
+	uint32_t ddi_func_ctrl = graphics_gtt_read(TRANS_DDI_FUNC_CTL_A);
+	ddi_func_ctrl &= TRANS_DDI_PORT_MASK;
+
+	/*
+	 * Check if transcoder is none or connected to DDI-A port (aka eDP).
+	 * Report no external display in both cases.
+	 */
+	if (ddi_func_ctrl == TRANS_DDI_PORT_NONE) {
+		return 0;
+	} else {
+		if (ddi_func_ctrl == TRANS_DDI_SELECT_PORT(PORT_A))
+			return 0;
+		else
+			return 1;
+	}
+}
+
+/* Check and report if an external display is attached */
+int fsp_soc_report_external_display(void)
+{
+	return graphics_get_framebuffer_address() && get_external_display_status();
+}
+
 static void gma_init(struct device *const dev)
 {
 	intel_gma_init_igd_opregion();