Re: [PATCH v3 1/8] drm/i915/vrr: Add per-CRTC vrr/cmrr debugfs control

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

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Hi Mitul,

On 7/14/2026 4:09 PM, Mitul Golani wrote:
> Add a per-CRTC debugfs file 'intel_vrr_cmrr' 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)
>
> Signed-off-by: Mitul Golani<mitulkumar.ajitkumar.golani@intel.com>
> ---
>   .../drm/i915/display/intel_display_debugfs.c  |   2 +
>   .../drm/i915/display/intel_display_types.h    |   5 +
>   drivers/gpu/drm/i915/display/intel_vrr.c      | 103 ++++++++++++++++++
>   drivers/gpu/drm/i915/display/intel_vrr.h      |   2 +
>   4 files changed, 112 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_debugfs.c b/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> index 3f02868ef105..2bbf4760dc30 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_debugfs.c
> +++ b/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);
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index c048da7d6fea..84a6d016e226 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1546,6 +1546,11 @@ struct intel_crtc {
>   		u64 flip_count;
>   	} dc_balance;
>   
> +	struct {
> +		u32 numerator;
> +		u32 denominator;
> +	} force_cmrr;
> +
>   	int scanline_offset;
>   
>   	struct {
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> index 51e4f3309b8b..8b6e36ee9f55 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> +++ b/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>
>   
> @@ -1231,3 +1235,102 @@ 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;
> +
> +	if (*numerator == 0)
> +		return -EINVAL;
> +
> +	if (*denominator != 1000 && *denominator != 1001)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static int intel_vrr_debugfs_cmrr_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_cmrr_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, intel_vrr_debugfs_cmrr_show, inode->i_private);
> +}
> +
> +static ssize_t intel_vrr_debugfs_cmrr_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;
> +
> +	crtc->force_cmrr.numerator = numerator;
> +	crtc->force_cmrr.denominator = denominator;
> +
> +	return len;
> +}
> +
> +static const struct file_operations intel_vrr_debugfs_cmrr_fops = {
> +	.owner = THIS_MODULE,
> +	.open = intel_vrr_debugfs_cmrr_open,
> +	.read = seq_read,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +	.write = intel_vrr_debugfs_cmrr_write,
> +};
> +
> +void intel_vrr_crtc_debugfs_add(struct intel_crtc *crtc)
> +{
> +	struct intel_display *display = to_intel_display(crtc);
> +
> +	if (!HAS_VRR(display))
> +		return;
> +
> +	if (HAS_CMRR(display))
> +		debugfs_create_file("intel_vrr_cmrr", 0600, crtc->base.debugfs_entry,
> +				    crtc, &intel_vrr_debugfs_cmrr_fops);
> +}
The debugfs interface accepts non-zero values, but fails to reset the 
value to zero.
> +
> diff --git a/drivers/gpu/drm/i915/display/intel_vrr.h b/drivers/gpu/drm/i915/display/intel_vrr.h
> index 55e9c429f579..19c7990be1b2 100644
> --- a/drivers/gpu/drm/i915/display/intel_vrr.h
> +++ b/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__ */

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