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

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

On Mon, 30 Sep 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.
> Spec: DP2.1a

Why send patches on top of a baseline that's 20 days old? Please rebase
and build before sending. Always.

> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c       | 6 ++++++
>  drivers/gpu/drm/i915/display/intel_display_types.h | 1 +
>  drivers/gpu/drm/i915/display/intel_dp_mst.c        | 9 +++++++++
>  drivers/gpu/drm/i915/i915_reg.h                    | 3 +++
>  4 files changed, 19 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 78ce402a5cd0..027ab45d4d38 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2095,6 +2095,7 @@ void intel_modeset_put_crtc_power_domains(struct intel_crtc *crtc,
>  static void i9xx_configure_cpu_transcoder(const struct intel_crtc_state *crtc_state)
>  {
>  	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> +	struct drm_i915_private *i915 = to_i915(crtc->base.dev);

struct intel_display.

>  	enum transcoder cpu_transcoder = crtc_state->cpu_transcoder;
>  
>  	if (intel_crtc_has_dp_encoder(crtc_state)) {
> @@ -2102,6 +2103,11 @@ static void i9xx_configure_cpu_transcoder(const struct intel_crtc_state *crtc_st
>  					       &crtc_state->dp_m_n);
>  		intel_cpu_transcoder_set_m2_n2(crtc, cpu_transcoder,
>  					       &crtc_state->dp_m2_n2);
> +
> +		if (DISPLAY_VER(i915) >= 20 && crtc_state->dp_m_n.min_hblank)
> +			intel_de_write(i915,
> +				       DP_MIN_HBLANK_CTL(i915, cpu_transcoder),
> +				       crtc_state->dp_m_n.min_hblank);

Doesn't feel right programming this here. Doesn't feel right having DP
checks here.

Where is this cleared?

The state readout and verification is missing.

>  	}
>  
>  	intel_set_transcoder_timings(crtc_state);
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index fa03157554b2..8d18545a369f 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -1028,6 +1028,7 @@ struct intel_link_m_n {
>  	u32 data_n;
>  	u32 link_m;
>  	u32 link_n;
> +	u32 min_hblank;

Doesn't feel right adding this here, not much to do with M/N.

>  };
>  
>  struct intel_csc_matrix {
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 15541932b809..c8f045142881 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -130,6 +130,8 @@ static void intel_dp_mst_compute_m_n(const struct intel_crtc_state *crtc_state,
>  {
>  	const struct drm_display_mode *adjusted_mode =
>  		&crtc_state->hw.adjusted_mode;
> +	u8 symbol_size = intel_dp_is_uhbr(crtc_state) ? 32 : 8;

Just use int.

> +	u32 hblank;
>  
>  	/* TODO: Check WA 14013163432 to set data M/N for full BW utilization. */
>  	intel_link_compute_m_n(bpp_x16, crtc_state->lane_count,
> @@ -139,6 +141,13 @@ static void intel_dp_mst_compute_m_n(const struct intel_crtc_state *crtc_state,
>  			       m_n);
>  
>  	m_n->tu = DIV_ROUND_UP_ULL(mul_u32_u32(m_n->data_m, 64), m_n->data_n);
> +
> +	/* 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))
> +		m_n->min_hblank = hblank > 5 ? hblank : 5;
> +	else
> +		m_n->min_hblank = hblank > 3 ? hblank : 3;
>  }
>  
>  static int intel_dp_mst_calc_pbn(int pixel_clock, int bpp_x16, int bw_overhead)
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index 41f4350a7c6c..65133efe728c 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1109,6 +1109,7 @@
>  #define _BCLRPAT_A		0x60020
>  #define _TRANS_VSYNCSHIFT_A	0x60028
>  #define _TRANS_MULT_A		0x6002c
> +#define _DP_MIN_HBLANK_CTL_A	0x600ac
>  
>  /* Pipe/transcoder B timing regs */
>  #define _TRANS_HTOTAL_B		0x61000
> @@ -1121,6 +1122,7 @@
>  #define _BCLRPAT_B		0x61020
>  #define _TRANS_VSYNCSHIFT_B	0x61028
>  #define _TRANS_MULT_B		0x6102c
> +#define _DP_MIN_HBLANK_CTL_B	0x610ac
>  
>  /* DSI 0 timing regs */
>  #define _TRANS_HTOTAL_DSI0	0x6b000
> @@ -1146,6 +1148,7 @@
>  #define TRANS_VSYNCSHIFT(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans), _TRANS_VSYNCSHIFT_A)
>  #define PIPESRC(dev_priv, pipe)		_MMIO_TRANS2(dev_priv, (pipe), _PIPEASRC)
>  #define TRANS_MULT(dev_priv, trans)	_MMIO_TRANS2(dev_priv, (trans), _TRANS_MULT_A)
> +#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)

-- 
Jani Nikula, Intel