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

On 7/16/2026 8:07 PM, Naladala, Ramanaidu wrote:
> Hi Mitul,
> 
> Resending this, as it was previously sent only to i915 by mistake.
> 
>> 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 <[email protected]>
>> ---
>>   .../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.
> 

Yeah I think we will also need some magic value to let the driver know 
to disable the feature. Since 0/0 is the default value shown by the 
debugfs entry that makes the most sense.

echo '0/0' > <file name>

to disable the CMRR. IGT can use it restore the state after testing is done.

>> +
>> 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__ */