From f53fe8ab3cd61b185e5eb3ba1af174175fc78725 Mon Sep 17 00:00:00 2001
From: Dom Cobley <popcornmix@gmail.com>
Date: Fri, 15 Sep 2023 17:25:17 +0100
Subject: [PATCH] drm/edid: Add option to report basic audio support with a
 generic edid

Hardware that fails to read the edid is quite common.
The kernel provides a mechanism to use one a of a few
pre-built generic edid files for getting a basic video mode.

However there is no easy was to add basic audio support,
which requires a CTA extension block to report capabilities.

Add an module option to request this.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
---
 drivers/gpu/drm/drm_edid.c      | 17 +++++++++++++++++
 drivers/gpu/drm/drm_edid_load.c | 34 +++++++++++++++++++++++++++++++++
 include/drm/drm_edid.h          |  2 ++
 3 files changed, 53 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 739e0d40cca619..419110878412a9 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -2090,6 +2090,23 @@ static struct edid *edid_filter_invalid_blocks(struct edid *edid,
 	return new;
 }
 
+/*
+ * add a CTA extension (block) containing audio support
+ * fix up the base extension to include the extra
+ * extension and report as digital (required for audio)
+ * and fix up checksums.
+ */
+void drm_edid_add_audio_extension(void *block)
+{
+	struct edid *edid = block;
+
+	edid->input = DRM_EDID_INPUT_DIGITAL;
+	edid->extensions++;
+	edid->checksum = edid_block_compute_checksum(edid);
+	edid = block + EDID_LENGTH;
+	edid->checksum = edid_block_compute_checksum(edid);
+}
+
 #define DDC_SEGMENT_ADDR 0x30
 /**
  * drm_do_probe_ddc_edid() - get EDID information via I2C
diff --git a/drivers/gpu/drm/drm_edid_load.c b/drivers/gpu/drm/drm_edid_load.c
index 37d8ba3ddb46af..4cedc674a93181 100644
--- a/drivers/gpu/drm/drm_edid_load.c
+++ b/drivers/gpu/drm/drm_edid_load.c
@@ -167,20 +167,53 @@ static int edid_size(const u8 *edid, int data_size)
 	return (edid[0x7e] + 1) * EDID_LENGTH;
 }
 
+/* Minimal edid extension block that reports basic audio support */
+static const u8 generic_edid_audio[] = {
+	0x02, /* CTA extension block */
+	0x03, /* version */
+	0x12, /* 18 bytes are valid */
+	0xc0, /* underscan | basic audio */
+	0x23, /* Audio Data Block, length 3 */
+	0x09, /* Linear PCM, 2 channel */
+	0x07, /* Supported sample rates (kHz): 48 44.1 32 */
+	0x07, /* Supported sample sizes (bits): 24 20 16 */
+	0x83, /* Speaker Allocation Data Block, length 3 */
+	0x01, 0x00, 0x00, /* FL/FR */
+	0x65, /* Vendor-Specific Data Block, length 3 */
+	0x03, 0x0c, 0x00, 0x00, 0x00, /* HDMI PA:0.0.0.0 */
+};
+
 static void *edid_load(struct drm_connector *connector, const char *name,
 			const char *connector_name)
 {
 	const struct firmware *fw = NULL;
 	const u8 *fwdata;
 	u8 *edid;
+	u8 *fwdata2 = NULL;
 	int fwsize, builtin;
 	int i, valid_extensions = 0;
 	bool print_bad_edid = !connector->bad_edid_counter || drm_debug_enabled(DRM_UT_KMS);
+	bool support_audio = false;
 
+	if (strncmp(name, "audio+", 6) == 0) {
+		support_audio = true;
+		name += 6;
+	}
 	builtin = match_string(generic_edid_name, GENERIC_EDIDS, name);
 	if (builtin >= 0) {
 		fwdata = generic_edid[builtin];
 		fwsize = sizeof(generic_edid[builtin]);
+		if (support_audio) {
+			fwdata2 = kzalloc(fwsize + EDID_LENGTH, GFP_KERNEL);
+			if (!fwdata2)
+				return ERR_PTR(-ENOMEM);
+
+			memcpy(fwdata2, fwdata, fwsize);
+			memcpy(fwdata2 + fwsize, generic_edid_audio, sizeof(generic_edid_audio));
+			drm_edid_add_audio_extension(fwdata2);
+			fwsize += EDID_LENGTH;
+			fwdata = fwdata2;
+		}
 	} else {
 		struct platform_device *pdev;
 		int err;
@@ -260,6 +293,7 @@ static void *edid_load(struct drm_connector *connector, const char *name,
 
 out:
 	release_firmware(fw);
+	kfree(fwdata2);
 	return edid;
 }
 
diff --git a/include/drm/drm_edid.h b/include/drm/drm_edid.h
index 1ed61e2b30a41c..72f33cd3c1d613 100644
--- a/include/drm/drm_edid.h
+++ b/include/drm/drm_edid.h
@@ -614,4 +614,6 @@ int drm_edid_connector_update(struct drm_connector *connector,
 const u8 *drm_find_edid_extension(const struct drm_edid *drm_edid,
 				  int ext_id, int *ext_index);
 
+void drm_edid_add_audio_extension(void *block);
+
 #endif /* __DRM_EDID_H__ */