[PATCH i-g-t v2 1/2] lib/igt_kms: Add MST bandwidth-fitting support and helpers

[Sowmiya S <sowmiya.s@intel.com>]

Add helpers to handle shared-link DP bandwidth fitting for
MST/daisy-chain configurations.

On MST hubs/daisy-chains multiple streams share one DP link
and a joint atomic commit can be rejected unless modes are
chosen to fit the link BW. This will centralizes MST detection
and fitting so tests can request fitting only when required.

v2: Remove the flag used for caching values and update the
function name to better describe its functionality (Jani)

Signed-off-by: Sowmiya S <sowmiya.s@intel.com>
---
 lib/igt_kms.c | 37 +++++++++++++++++++++++++++++++++++++
 lib/igt_kms.h |  2 ++
 2 files changed, 39 insertions(+)

diff --git a/lib/igt_kms.c b/lib/igt_kms.c
index 2efdfb85f..b6582fcbe 100644
--- a/lib/igt_kms.c
+++ b/lib/igt_kms.c
@@ -2744,6 +2744,7 @@ static void igt_output_reset(igt_output_t *output)
 {
 	output->pending_crtc = NULL;
 	output->use_override_mode = false;
+	output->bw_fit_applied = false;
 	memset(&output->override_mode, 0, sizeof(output->override_mode));
 
 	igt_output_set_prop_value(output, IGT_CONNECTOR_CRTC_ID, 0);
@@ -5376,6 +5377,7 @@ bool __override_all_active_output_modes_to_fit_bw(igt_display_t *display,
 		int ret;
 
 		igt_output_override_mode(output, mode);
+		output->bw_fit_applied = true;
 
 		if (__override_all_active_output_modes_to_fit_bw(display, outputs, n_outputs, base + 1))
 			return true;
@@ -5445,6 +5447,11 @@ bool igt_fit_modes_in_bw(igt_display_t *display)
 {
 	int ret;
 
+	igt_output_t *output;
+
+	for_each_output(display, output)
+		output->bw_fit_applied = false;
+
 	if (display->is_atomic)
 		ret = igt_display_try_commit_atomic(display,
 						    DRM_MODE_ATOMIC_TEST_ONLY |
@@ -5465,6 +5472,36 @@ bool igt_fit_modes_in_bw(igt_display_t *display)
 	return true;
 }
 
+/**
+ * igt_require_mst_link_bw:
+ * @display: a pointer to an #igt_display_t structure
+ *
+ * When two or more DP-MST streams share the same upstream link, a joint
+ * atomic commit may be rejected by the driver if the combined stream
+ * bandwidth exceeds the link capacity.  This function detects that
+ * situation and, when found, calls igt_fit_modes_in_bw() to select mode
+ * overrides that satisfy the shared-link BW budget.  The test is skipped
+ * if no valid combination can be found.  No-op when fewer than two active
+ * MST streams are present.
+ */
+void igt_require_mst_link_bw(igt_display_t *display)
+{
+	igt_output_t *output;
+	int active_mst = 0;
+
+	for_each_output(display, output) {
+		if (output->pending_crtc &&
+			igt_check_output_is_dp_mst(output))
+			active_mst++;
+	}
+
+	if (active_mst < 2)
+		return;
+
+	igt_require_f(igt_fit_modes_in_bw(display),
+			  "No valid mode combination fits available MST link BW\n");
+}
+
 /**
  * igt_crtc_refresh:
  * @crtc: CRTC to refresh
diff --git a/lib/igt_kms.h b/lib/igt_kms.h
index fcbb6a5ad..f8ba1a11e 100644
--- a/lib/igt_kms.h
+++ b/lib/igt_kms.h
@@ -506,6 +506,7 @@ typedef struct {
 
 	/* bitmask of changed properties */
 	uint64_t changed;
+	bool bw_fit_applied;
 
 	uint32_t props[IGT_NUM_CONNECTOR_PROPS];
 	uint64_t values[IGT_NUM_CONNECTOR_PROPS];
@@ -1286,6 +1287,7 @@ drmModePropertyBlobRes *igt_get_writeback_formats_blob(igt_output_t *output);
 uint64_t igt_get_writeback_fb_id(igt_output_t *output);
 void igt_detach_crtc(igt_display_t *display, igt_output_t *output);
 void igt_get_and_wait_out_fence(igt_output_t *output);
+void igt_require_mst_link_bw(igt_display_t *display);
 
 igt_colorop_t *igt_find_colorop(igt_display_t *display, uint32_t id);
 
-- 
2.48.1