Re: [PATCHv2] drm/i915/dp: Guarantee a minimum HBlank time

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 01 Oct 2024, Arun R Murthy <arun.r.murthy@intel.com> wrote:
> Mandate a minimum Hblank symbol cycle count between BS and BE in 8b/10b
> MST and 12b/132b mode.

Should be 128b.

What are BS and BE? I'm not asking specifically for *me*. The commit
message needs to have more clarity.

> Spec: DP2.1a
>
> v2: Affine calculation/updation of min HBlank to dp_mst (Jani)
>
> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
>  .../drm/i915/display/intel_display_types.h    |  2 ++
>  drivers/gpu/drm/i915/display/intel_dp_mst.c   | 30 +++++++++++++++++++
>  drivers/gpu/drm/i915/i915_reg.h               |  4 +++
>  3 files changed, 36 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 17fc21f6ae36..5f151ad9b878 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1770,6 +1770,8 @@ struct intel_dp {
>  
>  	u8 alpm_dpcd;
>  
> +	u32 min_hblank;
> +

Why would this be in intel_dp?

>  	struct {
>  		unsigned long mask;
>  	} quirks;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 4765bda154c1..45c8be7cd7b3 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -156,6 +156,30 @@ static int intel_dp_mst_calc_pbn(int pixel_clock, int bpp_x16, int bw_overhead)
>  	return DIV_ROUND_UP(effective_data_rate * 64, 54 * 1000);
>  }
>  
> +static void intel_dp_mst_compute_min_hblank(struct intel_crtc_state *crtc_state,
> +					    struct intel_connector *intel_connector,
> +					    int bpp_x16)
> +{
> +	struct intel_encoder *intel_encoder = intel_connector->encoder;
> +	struct intel_dp_mst_encoder *intel_mst = enc_to_mst(intel_encoder);
> +	struct intel_dp *intel_dp = &intel_mst->primary->dp;
> +	struct intel_display *intel_display = to_intel_display(intel_encoder);
> +	const struct drm_display_mode *adjusted_mode =
> +					&crtc_state->hw.adjusted_mode;
> +	u32 symbol_size = intel_dp_is_uhbr(crtc_state) ? 32 : 8;
> +	u32 hblank;
> +
> +	if (DISPLAY_VER(intel_display) < 20)
> +		return;
> +
> +	/* Calculate min Hblank Link Layer Symbol Cycle Count for 8b/10b MST & 128b/132b */
> +	hblank = DIV_ROUND_UP((DIV_ROUND_UP(adjusted_mode->htotal - adjusted_mode->hdisplay, 4) * bpp_x16), symbol_size);
> +	if (intel_dp_is_uhbr(crtc_state))
> +		intel_dp->min_hblank = hblank > 5 ? hblank : 5;
> +	else
> +		intel_dp->min_hblank = hblank > 3 ? hblank : 3;

Compute config must not mess with permanent data.

This should be in crtc state with readout and state checker etc.

BR,
Jani.

> +}
> +
>  static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
>  						struct intel_crtc_state *crtc_state,
>  						int max_bpp,
> @@ -228,6 +252,8 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
>  					 link_bpp_x16,
>  					 &crtc_state->dp_m_n);
>  
> +		intel_dp_mst_compute_min_hblank(crtc_state, connector, link_bpp_x16);
> +
>  		/*
>  		 * The TU size programmed to the HW determines which slots in
>  		 * an MTP frame are used for this stream, which needs to match
> @@ -1274,6 +1300,10 @@ static void intel_mst_enable_dp(struct intel_atomic_state *state,
>  			       TRANS_DP2_VFREQ_PIXEL_CLOCK(crtc_clock_hz & 0xffffff));
>  	}
>  
> +	if (DISPLAY_VER(dev_priv) >= 20)
> +		intel_de_write(dev_priv, DP_MIN_HBLANK_CTL(dev_priv, trans),
> +			       intel_dp->min_hblank);
> +
>  	enable_bs_jitter_was(pipe_config);
>  
>  	intel_ddi_enable_transcoder_func(encoder, pipe_config);
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 7396fc630e29..b321d136e1b0 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1138,6 +1138,10 @@
>  #define _TRANS_MULT_B		0x6102c
>  #define TRANS_MULT(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans), _TRANS_MULT_A)
>  
> +#define _DP_MIN_HBLANK_CTL_A	0x600ac
> +#define _DP_MIN_HBLANK_CTL_B	0x610ac
> +#define DP_MIN_HBLANK_CTL(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans), _DP_MIN_HBLANK_CTL_A)
> +
>  /* VGA port control */
>  #define ADPA			_MMIO(0x61100)
>  #define PCH_ADPA                _MMIO(0xe1100)

-- 
Jani Nikula, Intel