drm/i915: Use a fixed N value always

Windows/BIOS always uses fixed N values. Let's match that
behaviour.

Allows us to also get rid of that constant_n quirk stuff.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220907091057.11572-17-ville.syrjala@linux.intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index e7c28ff..c57b5b1 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2721,19 +2721,11 @@ 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);
 
@@ -2745,22 +2737,28 @@ 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(pixel_clock, link_clock,
-                   &m_n->link_m, &m_n->link_n,
-                   constant_n);
+       compute_m_n(&m_n->data_m, &m_n->data_n,
+                   data_clock, link_clock * nlanes * 8,
+                   0x8000000);
+
+       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 e895277..ae06153 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_display.h
+++ b/drivers/gpu/drm/i915/display/intel_display.h
@@ -547,7 +547,7 @@ 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 3b94715..2f9b1c0 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1927,7 +1927,7 @@ 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 =
@@ -1954,7 +1954,7 @@ 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)
@@ -2029,7 +2029,6 @@ 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)
@@ -2108,7 +2107,7 @@ 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)
@@ -2119,8 +2118,7 @@ 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 14d2a64..eafcc24 100644 (file)
--- 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 f67dd4f..7f47e5c 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_fdi.c
+++ b/drivers/gpu/drm/i915/display/intel_fdi.c
@@ -256,7 +256,7 @@ retry:
        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)