diff --git a/drivers/gpu/drm/apple/iomfb_template.c b/drivers/gpu/drm/apple/iomfb_template.c
index 34557f7ed1f4e..b29a7a96cbaa2 100644
--- a/drivers/gpu/drm/apple/iomfb_template.c
+++ b/drivers/gpu/drm/apple/iomfb_template.c
@@ -34,6 +34,13 @@
 #include "trace.h"
 #include "version_utils.h"
 
+#if DCP_FW_VERSION(26, 0, 0) <= DCP_FW_VER
+static bool experimental_h17p_1080p180_rgb8;
+module_param(experimental_h17p_1080p180_rgb8, bool, 0444);
+MODULE_PARM_DESC(experimental_h17p_1080p180_rgb8,
+		 "Diagnose advertised external 1080p180 SDR RGB8 timings marked unsafe");
+#endif
+
 /* Register defines used in bandwidth setup structure */
 #define REG_DOORBELL_BIT(idx) (2 + (idx))
 
@@ -1003,6 +1010,11 @@ static bool dcpep_process_chunks(struct apple_dcp *dcp,
 	}
 
 	if (!strcmp(req->key, "TimingElements")) {
+#if DCP_FW_VERSION(26, 0, 0) <= DCP_FW_VER
+		ctx.diagnostic_1080p180_rgb8 = experimental_h17p_1080p180_rgb8 &&
+			dcp->hw.iomfb_method_profile ==
+				DCP_IOMFB_METHODS_H17P_EXTERNAL_EXPERIMENTAL;
+#endif
 		dcp->modes = enumerate_modes(&ctx, &dcp->nr_modes,
 					     dcp->width_mm, dcp->height_mm,
 					     dcp->notch_height,
diff --git a/drivers/gpu/drm/apple/parser.c b/drivers/gpu/drm/apple/parser.c
index 8c2a1069417b6..d7fb1c1955651 100644
--- a/drivers/gpu/drm/apple/parser.c
+++ b/drivers/gpu/drm/apple/parser.c
@@ -526,10 +526,11 @@ static int parse_timing_color_restrictions(struct dcp_parse_ctx *handle,
 
 static int parse_color_modes(struct dcp_parse_ctx *handle,
 			     struct dcp_display_mode *out, bool external_sdr,
-			     const struct timing_color_restrictions *limits)
+			     const struct timing_color_restrictions *limits,
+			     struct dcp_color_mode *unsafe_rgb8)
 {
 	struct iterator outer_it;
-	unsigned int best_sdr_rank = 0;
+	unsigned int best_sdr_rank = 0, best_unsafe_rank = 0;
 	int ret = 0;
 	out->sdr_444.score = -1;
 	out->sdr_rgb.score = -1;
@@ -601,10 +602,24 @@ static int parse_color_modes(struct dcp_parse_ctx *handle,
 			unsigned int rank;
 
 			if (cmode.id <= U32_MAX &&
-			    (timing_color_contains(&limits->unsafe, cmode.id) ||
-			     timing_color_contains(&limits->dsc_required, cmode.id)))
+			    timing_color_contains(&limits->dsc_required, cmode.id))
 				continue;
 			rank = external_sdr_rank(&cmode);
+			if (cmode.id <= U32_MAX &&
+			    timing_color_contains(&limits->unsafe, cmode.id)) {
+				/*
+				 * Collect only a timing-local diagnostic candidate. Its
+				 * timing and opt-in scope are checked after the full parse.
+				 */
+				if (unsafe_rgb8 && cmode.depth == 8 && rank &&
+				    rank >= best_unsafe_rank) {
+					if (rank > best_unsafe_rank)
+						unsafe_rgb8->score = -1;
+					fill_color_mode(unsafe_rgb8, &cmode);
+					best_unsafe_rank = rank;
+				}
+				continue;
+			}
 			if (!rank || rank < best_sdr_rank)
 				continue;
 			if (rank > best_sdr_rank)
@@ -651,6 +666,9 @@ static int parse_mode(struct dcp_parse_ctx *handle,
 	struct iterator it;
 	struct dimension horiz = { .active = -1 }, vert = { .active = -1 };
 	struct timing_color_restrictions limits = {};
+	struct dcp_color_mode unsafe_rgb8 = { .score = -1 };
+	bool have_horiz = false, have_vert = false, have_virtual = false;
+	bool duplicate_scope = false;
 	s64 min_vrr = 0, max_vrr = 0;
 	u64 clock;
 	s64 id = -1;
@@ -687,21 +705,29 @@ static int parse_mode(struct dcp_parse_ctx *handle,
 			ret = PTR_ERR(key);
 		else if (is_virtual)
 			ret = skip(it.handle);
-		else if (!strcmp(key, "HorizontalAttributes"))
+		else if (!strcmp(key, "HorizontalAttributes")) {
+			duplicate_scope |= have_horiz;
+			have_horiz = true;
 			ret = parse_dimension(it.handle, &horiz, external_sdr);
-		else if (!strcmp(key, "VerticalAttributes"))
+		} else if (!strcmp(key, "VerticalAttributes")) {
+			duplicate_scope |= have_vert;
+			have_vert = true;
 			ret = parse_dimension(it.handle, &vert, external_sdr);
-		else if (!strcmp(key, "MinimumVariableRefreshRate"))
+		} else if (!strcmp(key, "MinimumVariableRefreshRate"))
 			ret = parse_int_bound(it.handle, &min_vrr, 0, U32_MAX);
 		else if (!strcmp(key, "MaximumVariableRefreshRate"))
 			ret = parse_int_bound(it.handle, &max_vrr, 0, U32_MAX);
 		else if (!strcmp(key, "ColorModes"))
-			ret = parse_color_modes(it.handle, out, external_sdr, &limits);
+			ret = parse_color_modes(it.handle, out, external_sdr, &limits,
+					handle->diagnostic_1080p180_rgb8 ?
+					&unsafe_rgb8 : NULL);
 		else if (!strcmp(key, "ID"))
 			ret = parse_int_bound(it.handle, &id, 0, U32_MAX);
-		else if (!strcmp(key, "IsVirtual"))
+		else if (!strcmp(key, "IsVirtual")) {
+			duplicate_scope |= have_virtual;
+			have_virtual = true;
 			ret = parse_bool(it.handle, &is_virtual);
-		else if (external_sdr && !strcmp(key, "IsPreferred")) {
+		} else if (external_sdr && !strcmp(key, "IsPreferred")) {
 			if (have_preferred)
 				ret = -EINVAL;
 			else
@@ -726,6 +752,25 @@ static int parse_mode(struct dcp_parse_ctx *handle,
 			return ret;
 		}
 	}
+	/*
+	 * Never replace a normal candidate or create a timing/color pairing.
+	 * This diagnostic only exposes an otherwise rejected firmware timing;
+	 * it neither repairs link timing nor establishes that "unsafe" is safe.
+	 * The observed 2080x1106 total and 11796583/65536 Hz are deliberate:
+	 * do not widen this to arbitrary nominal-180 Hz blanking or rates.
+	 */
+	if (external_sdr && !internal && handle->diagnostic_1080p180_rgb8 &&
+	    out->sdr_rgb.score < 0 && unsafe_rgb8.score >= 0 &&
+	    !duplicate_scope && have_horiz && have_vert && have_virtual && !is_virtual &&
+	    have_interlaced && !interlaced && !notch_height &&
+	    horiz.active == 1920 && vert.active == 1080 &&
+	    horiz.total == 2080 && vert.total == 1106 &&
+	    vert.precise_sync_rate == 11796583 &&
+	    horiz.pixel_repetition == 0 && vert.pixel_repetition == 0 &&
+	    horiz.sync_polarity >= 0 && vert.sync_polarity >= 0) {
+		out->sdr_rgb = unsafe_rgb8;
+		out->unsafe_rgb8_diagnostic = true;
+	}
 	if (out->sdr_rgb.score >= 0)
 		best_color_mode = out->sdr_rgb.id;
 	else if (out->sdr_444.score >= 0)
@@ -802,7 +847,8 @@ static int parse_mode(struct dcp_parse_ctx *handle,
 	if (external_sdr && horiz.sync_polarity >= 0 && vert.sync_polarity >= 0)
 		mode->flags = (horiz.sync_polarity ? DRM_MODE_FLAG_PHSYNC : DRM_MODE_FLAG_NHSYNC) |
 			      (vert.sync_polarity ? DRM_MODE_FLAG_PVSYNC : DRM_MODE_FLAG_NVSYNC);
-	out->metadata_timing_valid = external_sdr && have_preferred && preferred &&
+	out->metadata_timing_valid = external_sdr && !out->unsafe_rgb8_diagnostic &&
+		have_preferred && preferred &&
 		have_interlaced && !interlaced && horiz.pixel_repetition == 0 &&
 		vert.pixel_repetition == 0 && horiz.sync_polarity >= 0 && vert.sync_polarity >= 0;
 	drm_mode_set_name(mode);
@@ -862,7 +908,7 @@ struct dcp_display_mode *enumerate_modes(struct dcp_parse_ctx *handle,
 		/* Process a successful mode */
 		(*count)++;
 
-		if (score > best_score) {
+		if (!mode->unsafe_rgb8_diagnostic && score > best_score) {
 			best_score = score;
 			best_mode = mode;
 		}
diff --git a/drivers/gpu/drm/apple/parser.h b/drivers/gpu/drm/apple/parser.h
index 0392b09751ac9..7ba115fe417d6 100644
--- a/drivers/gpu/drm/apple/parser.h
+++ b/drivers/gpu/drm/apple/parser.h
@@ -15,6 +15,8 @@ struct dcp_parse_ctx {
 	struct apple_dcp *dcp;
 	const void *blob;
 	u32 pos, len;
+	/* Set only by the opt-in external H17P TimingElements caller. */
+	bool diagnostic_1080p180_rgb8;
 };
 
 enum dcp_color_eotf {
@@ -97,6 +99,7 @@ struct dcp_display_mode {
 	struct dcp_color_mode best;
 	bool vrr;
 	bool metadata_timing_valid;
+	bool unsafe_rgb8_diagnostic;
 };
 
 struct dimension {
diff --git a/tools/diagnostics/h17p-1080p180-rgb8.md b/tools/diagnostics/h17p-1080p180-rgb8.md
new file mode 100644
index 0000000000000..a3f87e372b04a
--- /dev/null
+++ b/tools/diagnostics/h17p-1080p180-rgb8.md
@@ -0,0 +1,37 @@
+# H17P external 1080p180 RGB8 diagnostic
+
+This is a default-off source diagnostic, not a production mode-policy change.
+The boot/load-time `experimental_h17p_1080p180_rgb8` appledrm parameter only
+reaches the experimental external H17P TimingElements parser. Normal parsing,
+other firmware profiles, internal panels and existing valid selections remain
+unchanged. The parser resets the opt-in for every new property blob.
+
+Only an otherwise rejected firmware timing can be exposed: explicit nonvirtual,
+progressive 1920x1080 with totals 2080x1106 and the captured fixed-point
+rate 11796583/65536 Hz (approximately 180.00157 Hz), with no pixel repetition
+and known sync polarities. Its own advertised ColorModes must contain a scored nonvirtual
+8-bit full-range SDR RGB candidate in sRGB, BT.709 or Default RGB. The exception
+applies only to UnsafeColorElementIDs; DSCRequiredColorElementIDs, malformed
+restriction lists, parser bounds and normal link/modeset checks still refuse.
+No global color ID is combined with a different timing. The timing fields and
+firmware IDs are kept as received, without changing link registers or blanking.
+
+An added diagnostic timing is never marked preferred and cannot supply the
+firmware-derived EDID preferred timing. This does not stop a compositor from
+restoring an explicitly saved mode, so use a separately reviewed controlled
+session and record the actual selection. Safe modes are not converted to RGB8.
+
+Before enabling on hardware, capture the current monitor/dock/physical route's
+TimingElements and confirm the local candidate, DSC list, full range, depth,
+clock and timing. A capture from a different dock/port is not evidence for the
+current route. The existing short-vblank firmware warning is not bypassed or
+reinterpreted; a successful advertisement alone proves no transport safety.
+Physical output, sustained presentation, errors and return to the baseline mode
+require separate qualification. Do not infer production safety or relax other
+guards from this diagnostic.
+
+`test-apple-external-sdr.py` exercises the production parser with the option off
+and on, malformed/DSC/range/depth/virtual/scope negatives, reversed dictionary
+order, timing-local candidates, and non-preferred diagnostic mode handling.
+Fixtures are independently generated protocol dictionaries with no private
+monitor payloads or identity fields.
diff --git a/tools/diagnostics/test-apple-external-sdr.py b/tools/diagnostics/test-apple-external-sdr.py
index 695a6059da419..852aae793a935 100644
--- a/tools/diagnostics/test-apple-external-sdr.py
+++ b/tools/diagnostics/test-apple-external-sdr.py
@@ -74,10 +74,12 @@ def timing(colors, rate=60, identity=203, score=10):
 
 cases = []
 
-def case(name, timings, external=True, count=1, identity=9, depth=8, clock=148500):
+def case(name, timings, external=True, count=1, identity=9, depth=8, clock=148500,
+         diagnostic=False, diagnostic_selected=False, preferred_index=0):
     out = bytearray(struct.pack('<I', 0xd3))
     wire(timings, out)
-    cases.append((name, bytes(out), external, count, identity, depth, clock))
+    cases.append((name, bytes(out), external, count, identity, depth, clock,
+                  diagnostic, diagnostic_selected, preferred_index))
 
 
 wide = color(84, 1000, Colorimetry=9, Depth=10)
@@ -167,6 +169,89 @@ def restricted(rate=60, unsafe=None, dsc=None, colors=None, before=False):
 case('duplicate ColorModes fail closed', [duplicate_colors], count=0)
 case('bad restriction skips only its timing', [restricted(180, [80, 85], []), restricted(60, [], [])], identity=85, depth=10)
 
+# Diagnostic-only retry: no private monitor identity or captured blob is embedded.
+# The binary dictionaries still go through the complete production parser.
+def trial_timing(colors=None, rate=180):
+    item = restricted(rate, [80, 85], [], colors)
+    item['IsInterlaced'] = False
+    item['HorizontalAttributes']['Total'] = 2080
+    item['VerticalAttributes'].update(Total=1106, PreciseSyncRate=11796583)
+    for axis in ('HorizontalAttributes', 'VerticalAttributes'):
+        item[axis].update(PixelRepetition=0, SyncPolarity=1)
+    return item
+
+
+def trial_case(name, item=None, **kwargs):
+    defaults = dict(identity=80, clock=414090, diagnostic=True,
+                    diagnostic_selected=True, preferred_index=-1)
+    defaults.update(kwargs)
+    case('diagnostic ' + name, [item if item is not None else trial_timing()], **defaults)
+
+trial_case('explicit enable exposes only RGB8')
+trial_case('default remains refused', diagnostic=False, count=0)
+trial_case('legacy keeps existing 10bit selection', external=False, identity=85,
+           depth=10, diagnostic_selected=False, preferred_index=0)
+case('internal diagnostic flag cannot admit unsafe timing', [trial_timing()],
+     diagnostic=True, count=0)
+item = trial_timing(); item['UnsafeColorElementIDs'] = [80]
+trial_case('existing safe candidate is not replaced', item, identity=85, depth=10,
+           diagnostic_selected=False, preferred_index=0)
+item = trial_timing(); item['DSCRequiredColorElementIDs'] = [80]
+trial_case('DSC remains forbidden', item, count=0)
+# No timing-local 8-bit entry: a global/sibling timing cannot provide one.
+trial_case('10bit-only timing remains refused', trial_timing([color85]), count=0)
+for label, changes in [
+    ('limited range', dict(DynamicRange=1)), ('HDR', dict(EOTF=2)),
+    ('YUV', dict(PixelEncoding=2)), ('wide gamut', dict(Colorimetry=9)),
+    ('12bit', dict(Depth=12)), ('virtual color', dict(IsVirtual=True)),
+    ('negative score', dict(Score=-1)), ('invalid ID', dict(ID=1 << 32)),
+]:
+    trial_case(label, trial_timing([color(80, 242999, **changes)]), count=0)
+for axis, key, value in [
+    ('HorizontalAttributes', 'Active', 1919),
+    ('VerticalAttributes', 'Active', 1079),
+    ('HorizontalAttributes', 'Total', 100),
+    ('VerticalAttributes', 'PreciseSyncRate', 11796582),
+    ('VerticalAttributes', 'PreciseSyncRate', 180 << 16),
+    ('HorizontalAttributes', 'Total', 2200),
+    ('VerticalAttributes', 'Total', 1125),
+    ('VerticalAttributes', 'PreciseSyncRate', 181 << 16),
+    ('HorizontalAttributes', 'PixelRepetition', 1),
+    ('VerticalAttributes', 'PixelRepetition', 1),
+    ('HorizontalAttributes', 'SyncPolarity', 2),
+]:
+    item = trial_timing(); item[axis][key] = value
+    trial_case(axis + key + str(value), item, count=0)
+for key in ('IsVirtual', 'IsInterlaced'):
+    item = trial_timing(); item.pop(key)
+    trial_case('missing ' + key, item, count=0)
+    item = trial_timing(); item[key] = True
+    trial_case('true ' + key, item, count=0)
+for axis in ('HorizontalAttributes', 'VerticalAttributes'):
+    for key in ('PixelRepetition', 'SyncPolarity'):
+        item = trial_timing(); item[axis].pop(key)
+        trial_case('missing ' + axis + key, item, count=0)
+for key in ('HorizontalAttributes', 'VerticalAttributes', 'IsVirtual'):
+    item = trial_timing()
+    duplicate = Pairs(list(item.items()) + [(key, item[key])])
+    trial_case('duplicate scope ' + key, duplicate, count=0)
+for key in ('UnsafeColorElementIDs', 'DSCRequiredColorElementIDs'):
+    item = trial_timing(); item[key] = [80, 80]
+    trial_case('duplicate restriction ' + key, item, count=0)
+# All key orders must preserve the same selection and non-preferred status.
+item = trial_timing()
+trial_case('reversed dictionary order', dict(reversed(list(item.items()))))
+item = trial_timing(); item['IsPreferred'] = True
+trial_case('firmware preferred does not promote trial', item)
+# A high firmware score must not make the trial the desktop default.
+item = trial_timing(); item['Score'] = 999999
+case('diagnostic trial cannot displace normal preferred mode', [item, restricted(60, [], [])],
+     count=2, identity=80, depth=8, clock=414090, diagnostic=True,
+     diagnostic_selected=True, preferred_index=1)
+# No shared candidate pool: successful sibling timing does not rescue an unsafe-only 10bit mode.
+case('diagnostic candidates remain timing-local', [trial_timing([color85]), restricted(60, [], [])],
+     identity=85, depth=10, diagnostic=True)
+
 prefix = r'''
 #include <assert.h>
 #include <stdbool.h>
@@ -220,12 +305,14 @@ def restricted(rate=60, unsafe=None, dsc=None, colors=None, before=False):
 int main(void)
 {
 '''
-for i, (name, blob, external, count, identity, depth, clock) in enumerate(cases):
+for i, (name, blob, external, count, identity, depth, clock, diagnostic, diagnostic_selected, preferred_index) in enumerate(cases):
     suffix += f'''
     {{
-        struct dcp_parse_ctx ctx;
+        struct dcp_parse_ctx ctx = {{ .diagnostic_1080p180_rgb8 = true }};
         unsigned int count = 99;
         assert(parse(blob_{i}, sizeof(blob_{i}), &ctx) == 0);
+        assert(!ctx.diagnostic_1080p180_rgb8);
+        ctx.diagnostic_1080p180_rgb8 = {str(diagnostic).lower()};
         struct dcp_display_mode *modes = enumerate_modes(&ctx, &count, 600, 340, 0,
                                                         {str(name.startswith('internal')).lower()}, {str(external).lower()});
         if (IS_ERR(modes) || count != {count}) {{
@@ -238,7 +325,10 @@ def restricted(rate=60, unsafe=None, dsc=None, colors=None, before=False):
         assert(modes[0].color_mode_id == {identity});
         assert(modes[0].sdr_rgb.depth == {depth});
         assert(modes[0].mode.clock == {clock});
-        assert(modes[0].mode.type & DRM_MODE_TYPE_PREFERRED);
+        assert(modes[0].unsafe_rgb8_diagnostic == {str(diagnostic_selected).lower()});
+        assert(!modes[0].unsafe_rgb8_diagnostic || !modes[0].metadata_timing_valid);
+        for (unsigned int mode = 0; mode < count; mode++)
+            assert(!!(modes[mode].mode.type & DRM_MODE_TYPE_PREFERRED) == ((int)mode == {preferred_index}));
 '''
     suffix += '        free(modes);\n    }\n'
 suffix += f'    puts("PASS: {len(cases)} production binary-parser SDR, malformed-input, legacy and high-refresh cases");\n    return 0;\n}}\n'