drm/i915/vrr: Add per-CRTC vrr/cmrr debugfs control

Add a per-CRTC debugfs file 'intel_vrr_target_refresh_rate' that lets
the user force a CMRR target refresh rate and video-mode requirement.

The file uses a "numerator/denominator" format:
  - numerator:   requested refresh rate in milli-Hz
                 (refresh rate in Hz * 1000, e.g. 60000 for 60 Hz)
  - denominator: 1000 for a 1:1 ratio (no video timing) or
                 1001 for the 1000/1001 video timing

Reading the file reports the currently stored values; writing updates
them. The file is created only on platforms with VRR and CMRR support.

--v2:
- Drop the "vrr" debugfs subdirectory and expose a single flat,
  intel_-prefixed "intel_vrr_cmrr" file (Jani, Nikula)
- Rename struct intel_crtc.cmrr to force_cmrr to make its purpose
  explicit (Chaitanya)
- Fix parse comment: numerator unit is milli-Hz, not KHz (Chaitanya)
- Add debugfs/intel_ prefixes to the debugfs handler functions (Chaitanya)
- Expand commit message with debugfs entry semantics (Chaitanya)

--v3:
- Rename debugfs function and file name (Chaitanya)
- Remove railing new line at EOF (Chaitanya)
- Update CMRR guard conditions (Chaitanya)
- Add 0/0 default case. (Ramanaidu)

--v4:
- Correct CMRR guard check while creating debugfs

--v5:
- Commit message update (Chaitanya)
- Add support for 0/0 writing (Validation)

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
Reviewed-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patch.msgid.link/20260730105919.3913412-4-mitulkumar.ajitkumar.golani@intel.com

drivers/gpu/drm/i915/display/intel_display_debugfs.c

@@ -49,6 +49,7 @@
 #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"
 
@@ -1395,6 +1396,7 @@ 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);

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1553,6 +1553,11 @@ struct intel_crtc {
 		u64 flip_count;
 	} dc_balance;
 
+	struct {
+		u32 numerator;
+		u32 denominator;
+	} force_cmrr;
+
 	int scanline_offset;
 
 	struct {

drivers/gpu/drm/i915/display/intel_vrr.c

@@ -4,6 +4,10 @@
  *
  */
 
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/string.h>
+
 #include <drm/drm_print.h>
 #include <drm/intel/step.h>
 
@@ -1237,3 +1241,111 @@ int intel_vrr_dcb_vmax_vblank_start_final(const struct intel_crtc_state *crtc_st
 
 	return intel_vrr_vblank_start(crtc_state, VRR_DCB_VMAX(tmp) + 1);
 }
+
+static
+int intel_vrr_cmrr_parse_ratio(char *str, u32 *numerator, u32 *denominator)
+{
+	char *sep;
+	int ret;
+
+	/*
+	 * Parse a "numerator/denominator" CMRR ratio string. The numerator
+	 * is the requested refresh rate in milli-Hz (refresh rate in Hz * 1000)
+	 * and the denominator selects the timing: 1000 for a 1:1 ratio
+	 * (no video timing) or 1001 for the 1000/1001 video timing.
+	 */
+
+	sep = strchr(str, '/');
+	if (!sep)
+		return -EINVAL;
+
+	*sep = '\0';
+
+	ret = kstrtou32(strim(str), 10, numerator);
+	if (ret)
+		return ret;
+
+	ret = kstrtou32(strim(sep + 1), 10, denominator);
+	if (ret)
+		return ret;
+	/*
+	 * "0/0" clears any previously configured CMRR override.
+	 * A zero numerator already means "CMRR not requested" in
+	 * intel_vrr_cmrr_compute_config(), so just let it through.
+	 */
+	if (*numerator == 0 && *denominator == 0)
+		return 0;
+
+	if (*numerator == 0)
+		return -EINVAL;
+
+	if (*denominator != 1000 && *denominator != 1001)
+		return -EINVAL;
+
+	return 0;
+}
+
+static int intel_vrr_debugfs_target_rr_show(struct seq_file *m, void *data)
+{
+	struct intel_crtc *crtc = m->private;
+
+	seq_printf(m, "%u/%u\n", crtc->force_cmrr.numerator, crtc->force_cmrr.denominator);
+
+	return 0;
+}
+
+static int intel_vrr_debugfs_target_rr_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, intel_vrr_debugfs_target_rr_show, inode->i_private);
+}
+
+static ssize_t intel_vrr_debugfs_target_rr_write(struct file *file, const char __user *ubuf,
+						 size_t len, loff_t *offp)
+{
+	struct seq_file *m = file->private_data;
+	struct intel_crtc *crtc = m->private;
+	u32 numerator, denominator;
+	char kbuf[32];
+	int ret;
+
+	if (len >= sizeof(kbuf))
+		return -EINVAL;
+
+	if (copy_from_user(kbuf, ubuf, len))
+		return -EFAULT;
+
+	kbuf[len] = '\0';
+
+	ret = intel_vrr_cmrr_parse_ratio(kbuf, &numerator, &denominator);
+	if (ret)
+		return ret;
+
+	if (crtc->force_cmrr.numerator == numerator &&
+	    crtc->force_cmrr.denominator == denominator)
+		return len;
+
+	crtc->force_cmrr.numerator = numerator;
+	crtc->force_cmrr.denominator = denominator;
+
+	return len;
+}
+
+static const struct file_operations intel_vrr_debugfs_target_rr_fops = {
+	.owner = THIS_MODULE,
+	.open = intel_vrr_debugfs_target_rr_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = single_release,
+	.write = intel_vrr_debugfs_target_rr_write,
+};
+
+void intel_vrr_crtc_debugfs_add(struct intel_crtc *crtc)
+{
+	struct intel_crtc_state *crtc_state = to_intel_crtc_state(crtc->base.state);
+
+	if (!intel_vrr_cmrr_possible(crtc_state))
+		return;
+
+	debugfs_create_file("intel_vrr_target_refresh_rate", 0600, crtc->base.debugfs_entry,
+			    crtc, &intel_vrr_debugfs_target_rr_fops);
+}

drivers/gpu/drm/i915/display/intel_vrr.h

@@ -56,4 +56,6 @@ 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);
 
+void intel_vrr_crtc_debugfs_add(struct intel_crtc *crtc);
+
 #endif /* __INTEL_VRR_H__ */