Re: [PATCH i-g-t v4 1/2] lib/igt_vrr:Add VRR helper library for display refresh rate testing

["Naladala, Ramanaidu" <Ramanaidu.naladala@intel.com>]

Hi Mitul,

Thanks for the review.

On 8/19/2026 9:33 PM, Golani, Mitulkumar Ajitkumar wrote:
>
>> -----Original Message-----
>> From: Naladala, Ramanaidu <ramanaidu.naladala@intel.com>
>> Sent: 12 August 2026 18:38
>> To: igt-dev@lists.freedesktop.org
>> Cc: Borah, Chaitanya Kumar <chaitanya.kumar.borah@intel.com>; Golani,
>> Mitulkumar Ajitkumar <mitulkumar.ajitkumar.golani@intel.com>; Naladala,
>> Ramanaidu <ramanaidu.naladala@intel.com>
>> Subject: [PATCH i-g-t v4 1/2] 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)
>>
> Please update change log, this helps reader to track what new changes are coming as part of this revision.
Sure. i will update this from next revision.
>
>> Signed-off-by: Naladala Ramanaidu <ramanaidu.naladala@intel.com>
>> ---
>>   lib/igt_vrr.c   | 154 ++++++++++++++++++++++++++++++++++++++++++++++++
>>   lib/igt_vrr.h   |  44 ++++++++++++++
>>   lib/meson.build |   1 +
>>   3 files changed, 199 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..704eaa3a3
>> --- /dev/null
>> +++ b/lib/igt_vrr.c
>> @@ -0,0 +1,154 @@
>> +// SPDX-License-Identifier: MIT
>> +/*
>> + * Copyright © 2026 Intel Corporation
>> + */
>> +
>> +#include <inttypes.h>
>> +
>> +#include "igt_vrr.h"
>> +#include "igt_sysfs.h"
>> +
>> +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 size_t igt_vrr_standard_video_timing_fps_count =
>> +	ARRAY_SIZE(igt_vrr_standard_video_timing_fps);
>> +
>> +/**
>> + * igt_target_rr_debugfs_write:
>> + * @fd: DRM file descriptor.
>> + * @crtc_index: Index of the CRTC.
>> + * @vrefresh: Target refresh rate to program.
>> + * @numerator: Numerator component of the target refresh rate fraction.
>> + * @denominator: Denominator component of the target refresh rate
>> fraction.
>> + *
>> + * Write the target refresh rate configuration to the per-CRTC
>> + * VRR debugfs interface.
>> + *
>> + * Returns: None.
>> + */
>> +void
>> +igt_target_rr_debugfs_write(int fd, int crtc_index,
>> +			    uint32_t vrefresh,
>> +			    uint32_t numerator,
>> +			    uint32_t denominator)
>> +{
>> +	char buf[32];
>> +	int ret, dir;
>> +	uint64_t val;
>> +
>> +	val = vrefresh * numerator;
> Use val = (uint64_t)vrefresh * numerator; for safety even though current ranges don't overflow.
sure. i will fix this in next revision.
>
>> +
>> +	snprintf(buf, sizeof(buf), "%" PRIu64 "/%u",
>> +		 val, denominator);
>> +
>> +	dir = igt_debugfs_crtc_dir(fd, crtc_index);
>> +	igt_require_fd(dir);
>> +
>> +	ret = igt_sysfs_write(dir, "intel_vrr_target_refresh_rate",
>> +			      buf, sizeof(buf) - 1);
> write the actual string length, not a fixed size. buf is uninitialized stack, so this sends garbage bytes after the terminating NUL
> to the kernel. Please write strlen(buf) and assert against that.
>
> "size_t n = strlen(buf);
> ret = igt_sysfs_write(dir, "intel_vrr_target_refresh_rate", buf, n);
> igt_assert_f(ret == n, "debugfs write failed\n");"
sure. i will fix this in next revision.
>
>> +	 close(dir);
>> +	 igt_assert_f(ret == (sizeof(buf) - 1), "debugfs_write failed"); }
>> +
>> +/**
>> + * igt_cmrr_debugfs_read:
>> + * @fd: DRM file descriptor.
>> + * @crtc_index: Index of the CRTC.
>> + *
>> + * Read the configured refresh rate from the per-CRTC VRR debugfs node.
>> + *
>> + * Return: None.
>> + */
>> +void
>> +igt_target_rr_debugfs_read(int fd, int crtc_index) {
> The above doc block says igt_cmrr_debugfs_read but the function is igt_target_rr_debugfs_read.
sure. i will fix this in next revision.
>
>> +	char buf[32];
>> +	int ret, dir;
>> +
>> +	dir = igt_debugfs_crtc_dir(fd, crtc_index);
>> +	igt_require_fd(dir);
>> +
>> +	ret = igt_sysfs_read(dir, "intel_vrr_target_refresh_rate",
>> +			     buf,  sizeof(buf) - 1);
>> +	close(dir);
>> +	igt_assert_f(ret >= 0,
>> +		     "Failed to read intel_vrr_target_refresh_rate.\n");
> The close(dir) and igt_assert_f(...) lines in the write helper use spaces; IGT uses tabs.
sure. i will fix this in next revision.
>
>> +
>> +	buf[ret] = '\0';
>> +
>> +	igt_info("vrr target RR: %s\n", buf);
>> +}
>> +
>> +/**
>> + * 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_get_mode_with_video_timing:
>> + * @output: Display output containing connector mode list
>> + * @fps: Requested integer refresh rate in Hz
>> + * @matched_mode: Returned mode that matches @fps
>> + *
>> + * Find and return a connector mode that matches the requested
>> + * video timing refresh rate in Hz.
>> + *
>> + * Returns: true when a mode is found, false otherwise  */
>> +
>> +bool igt_vrr_get_mode_with_video_timing(igt_output_t *output,
>> +					uint32_t fps,
>> +					drmModeModeInfo
>> *matched_mode)
>> +{
>> +	drmModeConnectorPtr connector;
>> +
>> +	connector = output->config.connector;
>> +	if (!connector)
>> +		return false;
>> +
>> +	for (int i = 0; i < connector->count_modes; i++) {
>> +		if (connector->modes[i].vrefresh == fps) {
>> +			*matched_mode = connector->modes[i];
>> +			return true;
>> +		}
>> +	}
>> +	return false;
>> +}
>> +
>> +/**
>> + * cmrr_supported:
>> + * @fd: DRM device file descriptor.
>> + * @crtc_index: Index of the CRTC.
>> + *
>> + * Checks whether the intel_vrr_target_refresh_rate debugfs node is
>> +present
>> + * for the specified CRTC, indicating CMRR support.
>> + *
>> + * Returns: true if CMRR is supported, false otherwise.
>> + */
>> +bool cmrr_supported(int fd, int crtc_index) {
> add the igt_ namespace prefix. cmrr_supported in a shared lib is inconsistent with every other exported symbol.
> Rename to igt_vrr_cmrr_supported() (update the header and callers).
sure. i will fix this in next revision.
>
>> +	int dir;
>> +
>> +	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..a317d4684
>> --- /dev/null
>> +++ b/lib/igt_vrr.h
>> @@ -0,0 +1,44 @@
>> +/* 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"
>> +
>> +#define CMRR_NUMERATOR 1000ULL
>> +#define CMRR_DENOMINATOR 1000ULL
>> +#define CMRR_VIDEO_MODE_DENOMINATOR 1001ULL #define
>> +TARGET_RR_SAMP_COUNT 100
>> +
>> +enum {
>> +	CMRR_VIDEO_MODE,
>> +	CMRR_NON_VIDEO_MODE,
>> +	CMRR_DISABLE,
>> +};
>> +
>> +extern const uint32_t igt_vrr_standard_video_timing_fps[];
>> +extern const size_t igt_vrr_standard_video_timing_fps_count;
>> +
>> +void
>> +igt_target_rr_debugfs_write(int fd, int crtc_index,
>> +			    uint32_t vrefresh,
>> +			    uint32_t numerator,
>> +			    uint32_t denominator);
>> +void
>> +igt_target_rr_debugfs_read(int fd, int crtc_index);
>> +
>> +double igt_vrr_mode_line_refresh_hz(const drmModeModeInfo *mode);
>> +
>> +bool igt_vrr_get_mode_with_video_timing(igt_output_t *output,
>> +					uint32_t fps,
>> +					drmModeModeInfo
>> *matched_mode);
>> +
>> +bool cmrr_supported(int fd, int crtc_index);
>> +
>> +#endif
>> diff --git a/lib/meson.build b/lib/meson.build index 3001b473e..8675bd4a6
>> 100644
>> --- a/lib/meson.build
>> +++ b/lib/meson.build
>> @@ -22,6 +22,7 @@ lib_sources = [
>>   	'igt_configfs.c',
>>   	'igt_facts.c',
>>   	'igt_crc.c',
>> +        'igt_vrr.c',
>>   	'igt_debugfs.c',
>>   	'igt_device.c',
>>   	'igt_device_scan.c',
>> --
>> 2.43.0