Re: [Intel-gfx] [PATCH 24/26] drm/i915: Use a fixed N value always

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

On Tue, 03 May 2022, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Windows/BIOS always uses fixed N values. Let's match that
> behaviour.
>
> Allows us to also get rid of that constant_n quirk stuff.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 36 +++++++++-----------
>  drivers/gpu/drm/i915/display/intel_display.h |  2 +-
>  drivers/gpu/drm/i915/display/intel_dp.c      | 10 +++---
>  drivers/gpu/drm/i915/display/intel_dp_mst.c  |  3 +-
>  drivers/gpu/drm/i915/display/intel_fdi.c     |  2 +-
>  5 files changed, 24 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index f30bdcdd4c84..89a7c8c1be28 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -2848,19 +2848,11 @@ intel_reduce_m_n_ratio(u32 *num, u32 *den)
>  	}
>  }
>  
> -static void compute_m_n(unsigned int m, unsigned int n,
> -			u32 *ret_m, u32 *ret_n,
> -			bool constant_n)
> +static void compute_m_n(u32 *ret_m, u32 *ret_n,
> +			u32 m, u32 n, u32 constant_n)
>  {
> -	/*
> -	 * Several DP dongles in particular seem to be fussy about
> -	 * too large link M/N values. Give N value as 0x8000 that
> -	 * should be acceptable by specific devices. 0x8000 is the
> -	 * specified fixed N value for asynchronous clock mode,
> -	 * which the devices expect also in synchronous clock mode.
> -	 */
>  	if (constant_n)
> -		*ret_n = DP_LINK_CONSTANT_N_VALUE;
> +		*ret_n = constant_n;
>  	else
>  		*ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
>  
> @@ -2872,22 +2864,28 @@ void
>  intel_link_compute_m_n(u16 bits_per_pixel, int nlanes,
>  		       int pixel_clock, int link_clock,
>  		       struct intel_link_m_n *m_n,
> -		       bool constant_n, bool fec_enable)
> +		       bool fec_enable)
>  {
>  	u32 data_clock = bits_per_pixel * pixel_clock;
>  
>  	if (fec_enable)
>  		data_clock = intel_dp_mode_to_fec_clock(data_clock);
>  
> +	/*
> +	 * Windows/BIOS uses fixed M/N values always. Follow suit.
> +	 *
> +	 * Also several DP dongles in particular seem to be fussy
> +	 * about too large link M/N values. Presumably the 20bit
> +	 * value used by Windows/BIOS is acceptable to everyone.
> +	 */
>  	m_n->tu = 64;
> -	compute_m_n(data_clock,
> -		    link_clock * nlanes * 8,
> -		    &m_n->data_m, &m_n->data_n,
> -		    constant_n);
> +	compute_m_n(&m_n->data_m, &m_n->data_n,
> +		    data_clock, link_clock * nlanes * 8,
> +		    0x8000000);
>  
> -	compute_m_n(pixel_clock, link_clock,
> -		    &m_n->link_m, &m_n->link_n,
> -		    constant_n);
> +	compute_m_n(&m_n->link_m, &m_n->link_n,
> +		    pixel_clock, link_clock,
> +		    0x80000);
>  }
>  
>  static void intel_panel_sanitize_ssc(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
> index 187910d94ec6..862338b6c4fa 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.h
> +++ b/drivers/gpu/drm/i915/display/intel_display.h
> @@ -546,7 +546,7 @@ u8 intel_calc_active_pipes(struct intel_atomic_state *state,
>  void intel_link_compute_m_n(u16 bpp, int nlanes,
>  			    int pixel_clock, int link_clock,
>  			    struct intel_link_m_n *m_n,
> -			    bool constant_n, bool fec_enable);
> +			    bool fec_enable);
>  u32 intel_plane_fb_max_stride(struct drm_i915_private *dev_priv,
>  			      u32 pixel_format, u64 modifier);
>  enum drm_mode_status
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 9385178c7fd6..d10f05d40360 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1878,7 +1878,7 @@ static bool can_enable_drrs(struct intel_connector *connector,
>  static void
>  intel_dp_drrs_compute_config(struct intel_connector *connector,
>  			     struct intel_crtc_state *pipe_config,
> -			     int output_bpp, bool constant_n)
> +			     int output_bpp)
>  {
>  	struct drm_i915_private *i915 = to_i915(connector->base.dev);
>  	const struct drm_display_mode *downclock_mode =
> @@ -1906,7 +1906,7 @@ intel_dp_drrs_compute_config(struct intel_connector *connector,
>  
>  	intel_link_compute_m_n(output_bpp, pipe_config->lane_count, pixel_clock,
>  			       pipe_config->port_clock, &pipe_config->dp_m2_n2,
> -			       constant_n, pipe_config->fec_enable);
> +			       pipe_config->fec_enable);
>  
>  	/* FIXME: abstract this better */
>  	if (pipe_config->splitter.enable)
> @@ -1981,7 +1981,6 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  	struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>  	const struct drm_display_mode *fixed_mode;
>  	struct intel_connector *connector = intel_dp->attached_connector;
> -	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CONSTANT_N);
>  	int ret = 0, output_bpp;
>  
>  	if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv) && encoder->port != PORT_A)
> @@ -2060,7 +2059,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  			       adjusted_mode->crtc_clock,
>  			       pipe_config->port_clock,
>  			       &pipe_config->dp_m_n,
> -			       constant_n, pipe_config->fec_enable);
> +			       pipe_config->fec_enable);
>  
>  	/* FIXME: abstract this better */
>  	if (pipe_config->splitter.enable)
> @@ -2071,8 +2070,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  
>  	intel_vrr_compute_config(pipe_config, conn_state);
>  	intel_psr_compute_config(intel_dp, pipe_config, conn_state);
> -	intel_dp_drrs_compute_config(connector, pipe_config,
> -				     output_bpp, constant_n);
> +	intel_dp_drrs_compute_config(connector, pipe_config, output_bpp);
>  	intel_dp_compute_vsc_sdp(intel_dp, pipe_config, conn_state);
>  	intel_dp_compute_hdr_metadata_infoframe_sdp(intel_dp, pipe_config, conn_state);
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 061b277e5ce7..00e55555091a 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -57,7 +57,6 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>  	struct drm_i915_private *i915 = to_i915(connector->base.dev);
>  	const struct drm_display_mode *adjusted_mode =
>  		&crtc_state->hw.adjusted_mode;
> -	bool constant_n = drm_dp_has_quirk(&intel_dp->desc, DP_DPCD_QUIRK_CONSTANT_N);
>  	int bpp, slots = -EINVAL;
>  
>  	crtc_state->lane_count = limits->max_lane_count;
> @@ -93,7 +92,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>  			       adjusted_mode->crtc_clock,
>  			       crtc_state->port_clock,
>  			       &crtc_state->dp_m_n,
> -			       constant_n, crtc_state->fec_enable);
> +			       crtc_state->fec_enable);
>  	crtc_state->dp_m_n.tu = slots;
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/i915/display/intel_fdi.c b/drivers/gpu/drm/i915/display/intel_fdi.c
> index 67d2484afbaa..0dc6414a56c4 100644
> --- a/drivers/gpu/drm/i915/display/intel_fdi.c
> +++ b/drivers/gpu/drm/i915/display/intel_fdi.c
> @@ -256,7 +256,7 @@ int ilk_fdi_compute_config(struct intel_crtc *crtc,
>  	pipe_config->fdi_lanes = lane;
>  
>  	intel_link_compute_m_n(pipe_config->pipe_bpp, lane, fdi_dotclock,
> -			       link_bw, &pipe_config->fdi_m_n, false, false);
> +			       link_bw, &pipe_config->fdi_m_n, false);
>  
>  	ret = ilk_check_fdi_lanes(dev, crtc->pipe, pipe_config);
>  	if (ret == -EDEADLK)

-- 
Jani Nikula, Intel Open Source Graphics Center