[PATCH i-g-t 1/2] tests/intel/kms_joiner_helper: Add igt_get_free_pipes_mask()

[Arun R Murthy <arun.r.murthy@intel.com>]

The joiner tests derive the set of usable pipes from the pipe count
alone, which assumes every pipe is free. A pipe already driven by
another client is then handed to a modeset, making the commit fail.

Add igt_get_free_pipes_mask(), which gets the current CRTC usage via
drmModeGetCrtcList() and translates it into a bitmask of hardware
pipes.

drmModeGetCrtcList() is a recent libdrm addition, so probe for it in
meson and fall back to plain CRTC enumeration when it is missing.

Assisted-by: LLM
Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
---
 meson.build                     |  7 +++++
 tests/intel/kms_joiner_helper.c | 66 +++++++++++++++++++++++++++++++++++++++++
 tests/intel/kms_joiner_helper.h |  1 +
 3 files changed, 74 insertions(+)

diff --git a/meson.build b/meson.build
index d7bbfd9698e5616ab777ac58128192ba1e0bec23..f41588c9d73361dbfd405de5ea8f764c6768a9c9 100644
--- a/meson.build
+++ b/meson.build
@@ -129,6 +129,13 @@ endif
 
 build_info += 'With libdrm: ' + ','.join(libdrm_info)
 
+# drmModeGetCrtcList() is a recent libdrm addition; keep building against
+# older libdrm by falling back to plain resource enumeration.
+if cc.has_function('drmModeGetCrtcList', dependencies : libdrm,
+		   prefix : '#include <xf86drmMode.h>')
+	config.set('HAVE_DRMMODEGETCRTCLIST', 1)
+endif
+
 pciaccess = dependency('pciaccess', version : '>=0.10')
 libkmod = dependency('libkmod')
 # igt_procps.c reads /proc directly; libprocps and libproc2 are not needed.
diff --git a/tests/intel/kms_joiner_helper.c b/tests/intel/kms_joiner_helper.c
index 36168030475c2725130e6c8ad924dcfb971a07f6..235e227fe9d82f598d0bd7df57ff65d73d717ad0 100644
--- a/tests/intel/kms_joiner_helper.c
+++ b/tests/intel/kms_joiner_helper.c
@@ -113,6 +113,72 @@ void igt_set_all_master_pipes_for_platform(igt_display_t *display, uint32_t *mas
 	}
 }
 
+/**
+ * igt_get_free_pipes_mask:
+ * @display: The display structure containing pipe information.
+ *
+ * Get the CRTCs that are currently usable and translate that into a
+ * bitmask of hardware pipes. A CRTC is reported free only when it is neither
+ * enabled through KMS nor active in hardware, so pipes claimed by another
+ * client (fbcon, a compositor, joiner) are never handed out to a modeset.
+ *
+ * The returned mask reflects the state at call time, so query it right before
+ * a modeset and after releasing the pipes a previous commit was using.
+ *
+ * Returns: bitmask of hardware pipes whose CRTC is free to be assigned. When
+ * libdrm lacks drmModeGetCrtcList() every pipe of @display is reported free.
+ */
+uint32_t igt_get_free_pipes_mask(igt_display_t *display)
+{
+	uint32_t free_mask = 0;
+#ifdef HAVE_DRMMODEGETCRTCLIST
+	drmModeCrtcListPtr list;
+	int i;
+
+	list = drmModeGetCrtcList(display->drm_fd);
+	igt_assert_f(list, "drmModeGetCrtcList() failed\n");
+
+	for (i = 0; i < list->count; i++) {
+		drmModeCrtcInfoPtr info = &list->crtcs[i];
+		igt_crtc_t *crtc = igt_crtc_for_crtc_id(display, info->crtc_id);
+
+		/* A CRTC the display never enumerated is not ours to use. */
+		if (!crtc)
+			continue;
+
+		if (info->in_use) {
+			igt_debug("CRTC %s in use: %ux%u, fb %u\n",
+				  igt_crtc_name(crtc), info->width,
+				  info->height, info->buffer_id);
+			continue;
+		}
+
+		if (info->driver_active) {
+			igt_debug("CRTC %s active in hardware, not enabled via KMS\n",
+				  igt_crtc_name(crtc));
+			continue;
+		}
+
+		free_mask |= BIT(crtc->hardware_pipe);
+	}
+
+	igt_info("%d of %d CRTCs free, free pipe mask 0x%x\n",
+		 list->count_available, list->count, free_mask);
+
+	drmModeFreeCrtcList(list);
+#else
+	igt_crtc_t *crtc;
+
+	for_each_crtc(display, crtc)
+		free_mask |= BIT(crtc->hardware_pipe);
+
+	igt_debug("libdrm has no drmModeGetCrtcList(), assuming pipe mask 0x%x free\n",
+		  free_mask);
+#endif
+
+	return free_mask;
+}
+
 /*
  * @drm_fd: DRM file descriptor
  * @outputs: array of pointers to igt_output_t
diff --git a/tests/intel/kms_joiner_helper.h b/tests/intel/kms_joiner_helper.h
index a0ab75b2c165084b643ead3f3ffc05cf5364e90b..14083d25c6f09e0577f123130697c34c2b6a15e4 100644
--- a/tests/intel/kms_joiner_helper.h
+++ b/tests/intel/kms_joiner_helper.h
@@ -11,6 +11,7 @@
 
 void igt_set_all_master_pipes_for_platform(igt_display_t *display,
 					   uint32_t *master_pipes);
+uint32_t igt_get_free_pipes_mask(igt_display_t *display);
 bool igt_assign_pipes_for_outputs(int drm_fd,
 				  igt_output_t **outputs,
 				  int num_outputs,

-- 
2.25.1