On 5/19/2026 10:33 AM, Mitul Golani wrote:
Add a per-CRTC debugfs entry 'vrr/cmrr_scaling' to allow reading and
writing the CMRR fraction level at runtime
for debug and testing purposes.
The file accepts three string values:
"Low" - Apply 1000/1001 fractional multiplier to vtotal
"Default" - Use nominal fixed refresh rate vtotal as-is
"High" - Apply 1001/1000 fractional multiplier to vtotal
Signed-off-by: Mitul Golani <[email protected]>
---
.../drm/i915/display/intel_display_debugfs.c | 2 +
drivers/gpu/drm/i915/display/intel_vrr.c | 85 +++++++++++++++++++
drivers/gpu/drm/i915/display/intel_vrr.h | 1 +
3 files changed, 88 insertions(+)
diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
index 81bef000a4e3..ae698560f306 100644
--- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
+++ b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
@@ -48,6 +48,7 @@
#include "intel_psr.h"
#include "intel_psr_regs.h"
#include "intel_vdsc.h"
+#include "intel_vrr.h"
#include "intel_wm.h"
#include "intel_tc.h"
@@ -1387,6 +1388,7 @@ void intel_crtc_debugfs_add(struct intel_crtc *crtc)
intel_drrs_crtc_debugfs_add(crtc);
intel_fbc_crtc_debugfs_add(crtc);
hsw_ips_crtc_debugfs_add(crtc);
+ intel_vrr_crtc_debugfs_add(crtc);
debugfs_create_file("i915_current_bpc", 0444, root, crtc,
&i915_current_bpc_fops);
diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c
b/drivers/gpu/drm/i915/display/intel_vrr.c
index bbc68c614667..e31778367245 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -20,6 +20,8 @@
#include "skl_prefill.h"
#include "skl_watermark.h"
+#include "linux/debugfs.h"
+
#include <linux/debugfs.h>
#define FIXED_POINT_PRECISION 100
#define CMRR_PRECISION_TOLERANCE 10
@@ -1227,3 +1229,86 @@ char *intel_vrr_cmrr_level_to_string(enum cmrr_level level)
return "Default";
}
}
+
+static int string_to_cmrr(const char *str, enum cmrr_level *level)
+{
+ if (sysfs_streq(str, "Low"))
+ *level = CMRR_LOW;
+ else if (sysfs_streq(str, "High"))
+ *level = CMRR_HIGH;
+ else if (sysfs_streq(str, "Default"))
+ *level = CMRR_DEFAULT;
+ else
+ return -EINVAL;
+
+ return 0;
+}
+
+static ssize_t cmrr_write(struct file *file,
+ const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct seq_file *s = file->private_data;
+ struct intel_crtc *crtc = s->private;
+ struct intel_crtc_state *crtc_state =
+ to_intel_crtc_state(crtc->base.state);
+ char kbuf[32];
+ enum cmrr_level level;
+ int ret;
+
+ if (count >= sizeof(kbuf))
+ return -EINVAL;
+
+ if (copy_from_user(kbuf, buf, count))
+ return -EFAULT;
+
+ kbuf[count] = '\0';
+
+ ret = string_to_cmrr(kbuf, &level);
+ if (ret)
+ return ret;
+
+ crtc_state->vrr.cmrr.level = level;
+
Will this not be over-written by intel_vrr_compute_fixed_rr_timings() ?
We would need an entry in struct intel_crtc to keep track of what the
user of the debugfs entry wants the driver to do and factor that in
intel_vrr_compute_fixed_rr_timings()
==
Chaitanya
+ return count;
+}
+
+static int cmrr_show(struct seq_file *s, void *data)
+{
+ struct intel_crtc *crtc = s->private;
+ struct intel_crtc_state *crtc_state =
+ to_intel_crtc_state(crtc->base.state);
+
+ seq_printf(s, "%s\n",
intel_vrr_cmrr_level_to_string(crtc_state->vrr.cmrr.level));
+
+ return 0;
+}
+
+static int cmrr_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, cmrr_show, inode->i_private);
+}
+
+static const struct file_operations cmrr_fops = {
+ .owner = THIS_MODULE,
+ .open = cmrr_open,
+ .read = seq_read,
+ .write = cmrr_write,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+
+void intel_vrr_crtc_debugfs_add(struct intel_crtc *crtc)
+{
+ struct dentry *root = crtc->base.debugfs_entry;
+ struct dentry *dir;
+
+ if (!root)
+ return;
+
+ dir = debugfs_create_dir("vrr", root);
+ if (IS_ERR(dir))
+ pr_err("debugfs creation : %ld\n", PTR_ERR(dir));
+
+ debugfs_create_file("cmrr_scaling", 0600, dir, crtc, &cmrr_fops);
+}
diff --git a/drivers/gpu/drm/i915/display/intel_vrr.h
b/drivers/gpu/drm/i915/display/intel_vrr.h
index 86707b8af2e3..9b52a0bf0e4f 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.h
+++ b/drivers/gpu/drm/i915/display/intel_vrr.h
@@ -55,5 +55,6 @@ int intel_vrr_dcb_vmax_vblank_start_next(const struct
intel_crtc_state *crtc_sta
int intel_vrr_dcb_vmin_vblank_start_final(const struct intel_crtc_state
*crtc_state);
int intel_vrr_dcb_vmax_vblank_start_final(const struct intel_crtc_state
*crtc_state);
char *intel_vrr_cmrr_level_to_string(enum cmrr_level level);
+void intel_vrr_crtc_debugfs_add(struct intel_crtc *crtc);
#endif /* __INTEL_VRR_H__ */
