Re: [PATCH v1 6/8] drm/i915/display: Add per-CRTC debugfs interface for CMRR fraction level

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

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 <mitulkumar.ajitkumar.golani@intel.com>
> ---
>   .../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__ */