Re: [PATCH] drm/i915/display: Enable AS SDP Skip Frames

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Tue, Feb 24, 2026 at 02:37:07AM +0530, Uma Shankar wrote:
> Hardware provides mechanism to skip AS SDP for programmed
> number of frames. Enable the same to drive to 1Hz if hardware
> supports it.
> 
> Signed-off-by: Uma Shankar <uma.shankar@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_alpm.c     | 3 +++
>  drivers/gpu/drm/i915/display/intel_psr_regs.h | 2 ++
>  2 files changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c b/drivers/gpu/drm/i915/display/intel_alpm.c
> index b3334bc4d0f9..76a8919cdba2 100644
> --- a/drivers/gpu/drm/i915/display/intel_alpm.c
> +++ b/drivers/gpu/drm/i915/display/intel_alpm.c
> @@ -395,6 +395,9 @@ static void lnl_alpm_configure(struct intel_dp *intel_dp,
>  			if (crtc_state->disable_as_sdp_when_pr_active)
>  				pr_alpm_ctl |= PR_ALPM_CTL_AS_SDP_TRANSMISSION_IN_ACTIVE_DISABLE;
>  
> +			if (DISPLAY_VER(display) >= 35)
> +				pr_alpm_ctl |= PR_ALPM_CTL_ASSDP_SKIP_FRAMES(32);

Where did that magic 32 frames come from?

This whole thing seems to involve a lot of details (Bspec:75539)
that someone needs to think through.

There are also some things in the DP 2.1a spec (eg. 2.18.8.1.1
Enabling Autonomous Sink Device Refresh Rate Timing) that seem
relevant for this stuff. Sadly the bspec page makes no mention
of any of this :/

> +
>  			intel_de_write(display, PR_ALPM_CTL(display, cpu_transcoder),
>  				       pr_alpm_ctl);
>  		}
> diff --git a/drivers/gpu/drm/i915/display/intel_psr_regs.h b/drivers/gpu/drm/i915/display/intel_psr_regs.h
> index 8afbf5a38335..8c35df795955 100644
> --- a/drivers/gpu/drm/i915/display/intel_psr_regs.h
> +++ b/drivers/gpu/drm/i915/display/intel_psr_regs.h
> @@ -268,6 +268,8 @@
>  
>  #define _PR_ALPM_CTL_A	0x60948
>  #define PR_ALPM_CTL(dev_priv, tran)	_MMIO_TRANS2(dev_priv, tran, _PR_ALPM_CTL_A)
> +#define  PR_ALPM_CTL_ASSDP_SKIP_FRAMES_MASK			REG_GENMASK(27, 16)
> +#define  PR_ALPM_CTL_ASSDP_SKIP_FRAMES(val)			REG_FIELD_PREP(PR_ALPM_CTL_ASSDP_SKIP_FRAMES_MASK, val)
>  #define  PR_ALPM_CTL_ALLOW_LINK_OFF_BETWEEN_AS_SDP_AND_SU	BIT(6)
>  #define  PR_ALPM_CTL_RFB_UPDATE_CONTROL				BIT(5)
>  #define  PR_ALPM_CTL_AS_SDP_TRANSMISSION_IN_ACTIVE_DISABLE	BIT(4)
> -- 
> 2.50.1

-- 
Ville Syrjälä
Intel