Re: [PATCH i-g-t v6 1/3] lib/igt_vrr: Add VRR helper library for display refresh rate testing

Introduce a new helper library for Variable Refresh Rate (VRR).

Add helpers to validate targeted refresh-rate testing.

v2: Modify debugfs with helpers.
v3: Add helper to check cmrr support.
     Address review comments. (Mitul)
v4: Address below review comments.
     - Add source and rationale for standard timing refresh
       rates. (Chaitanya)
     - Restrict target RR debugfs helper to Intel devices. (Chaitanya)
     - Make Intel target RR debugfs helper return bool instead of
       asserting in the library. (Mitul)
     - Avoid assertions in library functions and return status
       instead. (karthik)
     - Reorder source list as per naming convention.
     - Rename cmrr_supported() to igt_vrr_target_refresh_rate_supported()
       for consistency. (Chaitanya)
     - Move CMRR-specific macros and enums from the library to the test
       file. (Chaitanya)
v5: Address below review comments:
     - Add space after subject prefix. (Kamil)
     - Add blank line between system and local include headers. (Kamil)
     - meson: fix indentation for igt_vrr entry. (Kamil)
     - Rename target refresh rate helpers. (Chaitanya)
     - Change FPS count type to uint32_t. (Mitul)

Assisted-by: GitHub Copilot:Claude Opus 4.6
Signed-off-by: Naladala Ramanaidu <redacted>
---
  lib/igt_vrr.c   | 166 ++++++++++++++++++++++++++++++++++++++++++++++++
  lib/igt_vrr.h   |  30 +++++++++
  lib/meson.build |   1 +
  3 files changed, 197 insertions(+)
  create mode 100644 lib/igt_vrr.c
  create mode 100644 lib/igt_vrr.h

diff --git a/lib/igt_vrr.c b/lib/igt_vrr.c
new file mode 100644
index 000000000..1eaf0c3f7
--- /dev/null
+++ b/lib/igt_vrr.c

@@ -0,0 +1,166 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2026 Intel Corporation
+ */
+
+#include <inttypes.h>
+
+#include "igt_vrr.h"
+#include "igt_sysfs.h"
+
+/**
+ * Integer refresh rates that sinks advertise as standard video timings, and
+ * for which a fractional (rate * 1000/1001) counterpart is also defined:
+ *
+ *  - 24, 25, 30, 50 and 60 Hz are the film and broadcast (PAL/NTSC) cadences
+ *    carried over into the CTA-861 video formats.
+ *  - 48, 96, 100, 120, 200 and 240 Hz are the integer multiples of those
+ *    cadences, also listed as CTA-861 video formats.
+ *  - 75, 90, 144, 165 and 180 Hz are VESA DMT/CVT and adaptive-sync panel
+ *    rates in common use.
+ *

+ * The fractional variant of each entry (e.g. 60 -> 59.94) is what a target
+ * refresh rate in video mode programs.
+ */
+const uint32_t igt_vrr_standard_video_timing_fps[] = {
+	24, 25, 30, 48, 50, 60, 75, 90, 96, 100, 120, 144, 165, 180, 200, 240,
+};
+
+const uint32_t igt_vrr_standard_video_timing_fps_count =
+	ARRAY_SIZE(igt_vrr_standard_video_timing_fps);
+
+/**
+ * igt_vrr_target_rr_debugfs_write:
+ * @fd: DRM file descriptor.
+ * @crtc_index: Index of the CRTC.
+ * @rr_numerator: Numerator of the target refresh rate fraction.
+ * @rr_denominator: Denominator of the target refresh rate fraction.
+ *
+ * Write the target refresh rate configuration to the per-CRTC
+ * VRR debugfs interface. Passing 0/0 clears the target refresh
+ * rate.
+ *
+ * The debugfs interface is Intel specific, so this returns false on
+ * other drivers. Other drivers can add their own debugfs node here.
+ *
+ * Returns:
+ * true if the target refresh rate was written successfully, false otherwise.
+ */
+bool
+igt_vrr_target_rr_debugfs_write(int fd, int crtc_index,
+				uint32_t rr_numerator,
+				uint32_t rr_denominator)
+{
+	char buf[32];
+	int ret, dir, len;
+
+	if (!is_intel_device(fd)) {
+		igt_info("Not an Intel device\n");
+		return false;
+	}
+
+	len = snprintf(buf, sizeof(buf), "%u/%u", rr_numerator, rr_denominator);
+	if (len <= 0 || len >= (int)sizeof(buf))
+		return false;
+
+	dir = igt_debugfs_crtc_dir(fd, crtc_index);
+	if (dir < 0)
+		return false;
+
+	ret = igt_sysfs_write(dir, "intel_vrr_target_refresh_rate", buf, len);
+	close(dir);
+
+	return ret == len;
+}
+
+/**
+ * igt_vrr_target_rr_debugfs_read:
+ * @fd: DRM file descriptor.
+ * @crtc_index: Index of the CRTC.
+ * @buf: Buffer to store the target refresh rate string.
+ * @size: Size of @buf in bytes.
+ *
+ * Read the target refresh rate from the per-CRTC VRR debugfs interface.
+ * The returned string is always NUL-terminated on success.
+ *
+ * The debugfs interface is Intel specific, so this returns false on
+ * other drivers. Other drivers can add their own debugfs node here.
+ *
+ * Return:
+ * true if the target refresh rate was read successfully, false otherwise.
+ */
+bool
+igt_vrr_target_rr_debugfs_read(int fd, int crtc_index, char *buf, size_t size)
+{
+	int ret, dir;
+
+	if (!buf || !size)
+		return false;
+
+	if (!is_intel_device(fd)) {
+		igt_info("Not an Intel device\n");
+		return false;
+	}
+
+	dir = igt_debugfs_crtc_dir(fd, crtc_index);
+	if (dir < 0)
+		return false;
+
+	ret = igt_sysfs_read(dir, "intel_vrr_target_refresh_rate",
+			     buf, size - 1);
+	close(dir);
+
+	if (ret < 0)
+		return false;
+
+	buf[ret] = '\0';
+
+	return true;
+}
+
+/**
+ * igt_vrr_mode_line_refresh_hz:
+ * @mode: DRM display mode used for the calculation
+ *
+ * Compute the refresh rate directly from the mode timing parameters.
+ *
+ * Returns: Refresh rate in Hz as a floating-point value.
+ */
+double igt_vrr_mode_line_refresh_hz(const drmModeModeInfo *mode)
+{
+	return (double)mode->clock * 1000.0 / ((double)mode->htotal * (double)mode->vtotal);
+}
+
+/**
+ * igt_vrr_target_refresh_rate_supported:
+ * @fd: DRM device file descriptor.
+ * @crtc_index: Index of the CRTC.
+ *
+ * Checks whether the target refresh rate debugfs node is present for the
+ * specified CRTC, indicating CMRR support.
+ *
+ * The debugfs interface is Intel specific, so this returns false on
+ * other drivers. Other drivers can add their own debugfs node here.
+ *
+ * Returns: true if CMRR is supported, false otherwise.
+ */
+bool igt_vrr_target_refresh_rate_supported(int fd, int crtc_index)
+{
+	int dir;
+
+	if (!is_intel_device(fd))
+		return false;
+
+	dir = igt_debugfs_crtc_dir(fd, crtc_index);
+
+	if (dir < 0)
+		return false;
+
+	if (faccessat(dir, "intel_vrr_target_refresh_rate", F_OK, 0) == 0) {
+		close(dir);
+		return true;
+	}
+
+	close(dir);
+	return false;
+}

diff --git a/lib/igt_vrr.h b/lib/igt_vrr.h
new file mode 100644
index 000000000..84d26cd1d
--- /dev/null
+++ b/lib/igt_vrr.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2026 Intel Corporation
+ */
+
+#ifndef IGT_VRR_H
+#define IGT_VRR_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "igt.h"
+#include "igt_kms.h"
+
+extern const uint32_t igt_vrr_standard_video_timing_fps[];
+extern const uint32_t igt_vrr_standard_video_timing_fps_count;
+
+bool
+igt_vrr_target_rr_debugfs_write(int fd, int crtc_index,
+				uint32_t rr_numerator,
+				uint32_t rr_denominator);
+bool
+igt_vrr_target_rr_debugfs_read(int fd, int crtc_index,
+			       char *buf, size_t size);
+
+double igt_vrr_mode_line_refresh_hz(const drmModeModeInfo *mode);
+
+bool igt_vrr_target_refresh_rate_supported(int fd, int crtc_index);
+
+#endif

diff --git a/lib/meson.build b/lib/meson.build
index a7cde027e..d1a770b6d 100644
--- a/lib/meson.build
+++ b/lib/meson.build

@@ -56,6 +56,7 @@ lib_sources = [
  	'igt_vec.c',
  	'igt_vgem.c',
  	'igt_vkms.c',
+	'igt_vrr.c',
  	'igt_x86.c',
  	'instdone.c',
  	'intel_allocator.c',