CHROMIUM: drm: bridge/dw_hdmi: improved the hdmi audio N/CTS cacluate math

The original math would bring some inaccurate to N/CTS that would
caused those magic number won't fit the HDMI 1.4 Spec request:
	128 * SampleRate = Tmds * N / CTS;

So this time we try to improved to math of N that would find the
minimal inaccurate with the HDMI 1.4 Spec.

Change-Id: Ied3cde3c352d955ae6f15d5e7fb172e92316c2a5
Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Reviewed-on: https://chromium-review.googlesource.com/315424
Reviewed-by: Douglas Anderson <dianders@chromium.org>

diff --git a/drivers/gpu/drm/bridge/dw-hdmi.c b/drivers/gpu/drm/bridge/dw-hdmi.c
index 641d947259707af85f21a6236885b376a33b5c30..c28eb33adf1c12cfa6ddab7db8bda36909ab7c66 100644 (file)
--- a/drivers/gpu/drm/bridge/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/dw-hdmi.c
@@ -53,6 +53,62 @@ enum hdmi_datamap {
        YCbCr422_12B = 0x12,
 };
 
+/*
+ * Unless otherwise noted, entries in this table are 100% optimization.
+ * Values can be obtained from hdmi_compute_n() but that function is
+ * slow so we pre-compute values we expect to see.
+ *
+ * All 32k and 48k values are expected to be the same (due to the way
+ * the math works) for any rate that's an exact kHz.
+ */
+static const struct dw_hdmi_audio_tmds_n common_tmds_n_table[] = {
+       { .tmds = 25175000, .n_32k = 4096, .n_44k1 = 12854, .n_48k = 6144, },
+       { .tmds = 25200000, .n_32k = 4096, .n_44k1 = 5656, .n_48k = 6144, },
+       { .tmds = 27000000, .n_32k = 4096, .n_44k1 = 5488, .n_48k = 6144, },
+       { .tmds = 28320000, .n_32k = 4096, .n_44k1 = 5586, .n_48k = 6144, },
+       { .tmds = 30240000, .n_32k = 4096, .n_44k1 = 5642, .n_48k = 6144, },
+       { .tmds = 31500000, .n_32k = 4096, .n_44k1 = 5600, .n_48k = 6144, },
+       { .tmds = 32000000, .n_32k = 4096, .n_44k1 = 5733, .n_48k = 6144, },
+       { .tmds = 33750000, .n_32k = 4096, .n_44k1 = 6272, .n_48k = 6144, },
+       { .tmds = 36000000, .n_32k = 4096, .n_44k1 = 5684, .n_48k = 6144, },
+       { .tmds = 40000000, .n_32k = 4096, .n_44k1 = 5733, .n_48k = 6144, },
+       { .tmds = 49500000, .n_32k = 4096, .n_44k1 = 5488, .n_48k = 6144, },
+       { .tmds = 50000000, .n_32k = 4096, .n_44k1 = 5292, .n_48k = 6144, },
+       { .tmds = 54000000, .n_32k = 4096, .n_44k1 = 5684, .n_48k = 6144, },
+       { .tmds = 65000000, .n_32k = 4096, .n_44k1 = 7056, .n_48k = 6144, },
+       { .tmds = 68250000, .n_32k = 4096, .n_44k1 = 5376, .n_48k = 6144, },
+       { .tmds = 71000000, .n_32k = 4096, .n_44k1 = 7056, .n_48k = 6144, },
+       { .tmds = 72000000, .n_32k = 4096, .n_44k1 = 5635, .n_48k = 6144, },
+       { .tmds = 73250000, .n_32k = 4096, .n_44k1 = 14112, .n_48k = 6144, },
+       { .tmds = 74250000, .n_32k = 4096, .n_44k1 = 6272, .n_48k = 6144, },
+       { .tmds = 75000000, .n_32k = 4096, .n_44k1 = 5880, .n_48k = 6144, },
+       { .tmds = 78750000, .n_32k = 4096, .n_44k1 = 5600, .n_48k = 6144, },
+       { .tmds = 78800000, .n_32k = 4096, .n_44k1 = 5292, .n_48k = 6144, },
+       { .tmds = 79500000, .n_32k = 4096, .n_44k1 = 4704, .n_48k = 6144, },
+       { .tmds = 83500000, .n_32k = 4096, .n_44k1 = 7056, .n_48k = 6144, },
+       { .tmds = 85500000, .n_32k = 4096, .n_44k1 = 5488, .n_48k = 6144, },
+       { .tmds = 88750000, .n_32k = 4096, .n_44k1 = 14112, .n_48k = 6144, },
+       { .tmds = 97750000, .n_32k = 4096, .n_44k1 = 14112, .n_48k = 6144, },
+       { .tmds = 101000000, .n_32k = 4096, .n_44k1 = 7056, .n_48k = 6144, },
+       { .tmds = 106500000, .n_32k = 4096, .n_44k1 = 4704, .n_48k = 6144, },
+       { .tmds = 108000000, .n_32k = 4096, .n_44k1 = 5684, .n_48k = 6144, },
+       { .tmds = 115500000, .n_32k = 4096, .n_44k1 = 5712, .n_48k = 6144, },
+       { .tmds = 119000000, .n_32k = 4096, .n_44k1 = 5544, .n_48k = 6144, },
+       { .tmds = 135000000, .n_32k = 4096, .n_44k1 = 5488, .n_48k = 6144, },
+       { .tmds = 146250000, .n_32k = 4096, .n_44k1 = 6272, .n_48k = 6144, },
+       { .tmds = 148500000, .n_32k = 4096, .n_44k1 = 5488, .n_48k = 6144, },
+       { .tmds = 154000000, .n_32k = 4096, .n_44k1 = 5544, .n_48k = 6144, },
+       { .tmds = 162000000, .n_32k = 4096, .n_44k1 = 5684, .n_48k = 6144, },
+
+       /* For 297 MHz+ HDMI spec have some other rule for setting N */
+       { .tmds = 297000000, .n_32k = 3073, .n_44k1 = 4704, .n_48k = 5120, },
+       { .tmds = 594000000, .n_32k = 3073, .n_44k1 = 9408, .n_48k = 10240, },
+
+       /* End of table */
+       { .tmds = 0,         .n_32k = 0,    .n_44k1 = 0,    .n_48k = 0, },
+};
+
+
 static const u16 csc_coeff_default[3][4] = {
        { 0x2000, 0x0000, 0x0000, 0x0000 },
        { 0x0000, 0x2000, 0x0000, 0x0000 },
@@ -217,60 +273,117 @@ static void hdmi_set_cts_n(struct dw_hdmi *hdmi, unsigned int cts,
        hdmi_writeb(hdmi, n & 0xff, HDMI_AUD_N1);
 }
 
-static unsigned int hdmi_compute_n(unsigned int freq, unsigned long pixel_clk)
+static int hdmi_match_tmds_n_table(struct dw_hdmi *hdmi,
+                                  unsigned long pixel_clk,
+                                  unsigned long freq)
 {
-       unsigned int n = (128 * freq) / 1000;
-       unsigned int mult = 1;
+       const struct dw_hdmi_plat_data *plat_data = hdmi->plat_data;
+       const struct dw_hdmi_audio_tmds_n *tmds_n = NULL;
+       int i;
 
-       while (freq > 48000) {
-               mult *= 2;
-               freq /= 2;
+       if (plat_data->tmds_n_table) {
+               for (i = 0; plat_data->tmds_n_table[i].tmds != 0; i++) {
+                       if (pixel_clk == plat_data->tmds_n_table[i].tmds) {
+                               tmds_n = &plat_data->tmds_n_table[i];
+                               break;
+                       }
+               }
        }
 
+       if (tmds_n == NULL) {
+               for (i = 0; common_tmds_n_table[i].tmds != 0; i++) {
+                       if (pixel_clk == common_tmds_n_table[i].tmds) {
+                               tmds_n = &common_tmds_n_table[i];
+                               break;
+                       }
+               }
+       }
+
+       if (tmds_n == NULL)
+               return -ENOENT;
+
        switch (freq) {
        case 32000:
-               if (pixel_clk == 25175000)
-                       n = 4576;
-               else if (pixel_clk == 27027000)
-                       n = 4096;
-               else if (pixel_clk == 74176000 || pixel_clk == 148352000)
-                       n = 11648;
-               else
-                       n = 4096;
-               n *= mult;
-               break;
-
+               return tmds_n->n_32k;
        case 44100:
-               if (pixel_clk == 25175000)
-                       n = 7007;
-               else if (pixel_clk == 74176000)
-                       n = 17836;
-               else if (pixel_clk == 148352000)
-                       n = 8918;
-               else
-                       n = 6272;
-               n *= mult;
-               break;
-
+       case 88200:
+       case 176400:
+               return (freq / 44100) * tmds_n->n_44k1;
        case 48000:
-               if (pixel_clk == 25175000)
-                       n = 6864;
-               else if (pixel_clk == 27027000)
-                       n = 6144;
-               else if (pixel_clk == 74176000)
-                       n = 11648;
-               else if (pixel_clk == 148352000)
-                       n = 5824;
-               else
-                       n = 6144;
-               n *= mult;
-               break;
-
+       case 96000:
+       case 192000:
+               return (freq / 48000) * tmds_n->n_48k;
        default:
-               break;
+               return -ENOENT;
+       }
+}
+
+static u64 hdmi_audio_math_diff(unsigned int freq, unsigned int n,
+                               unsigned int pixel_clk)
+{
+       u64 final, diff;
+       u64 cts;
+
+       final = (u64)pixel_clk * n;
+
+       cts = final;
+       do_div(cts, 128 * freq);
+
+       diff = final - (u64)cts * (128 * freq);
+
+       return diff;
+}
+
+static unsigned int hdmi_compute_n(struct dw_hdmi *hdmi,
+                                  unsigned long pixel_clk,
+                                  unsigned long freq)
+{
+       unsigned int min_n = DIV_ROUND_UP((128 * freq), 1500);
+       unsigned int max_n = (128 * freq) / 300;
+       unsigned int ideal_n = (128 * freq) / 1000;
+       unsigned int best_n_distance = ideal_n;
+       unsigned int best_n = 0;
+       u64 best_diff = U64_MAX;
+       int n;
+
+       /* If the ideal N could satisfy the audio math, then just take it */
+       if (hdmi_audio_math_diff(freq, ideal_n, pixel_clk) == 0)
+               return ideal_n;
+
+       for (n = min_n; n <= max_n; n++) {
+               u64 diff = hdmi_audio_math_diff(freq, n, pixel_clk);
+
+               if (diff < best_diff || (diff == best_diff &&
+                   abs(n - ideal_n) < best_n_distance)) {
+                       best_n = n;
+                       best_diff = diff;
+                       best_n_distance = abs(best_n - ideal_n);
+               }
+
+               /*
+                * The best N already satisfy the audio math, and also be
+                * the closest value to ideal N, so just cut the loop.
+                */
+               if ((best_diff == 0) && (abs(n - ideal_n) > best_n_distance))
+                       break;
        }
 
-       return n;
+       return best_n;
+}
+
+static unsigned int hdmi_find_n(struct dw_hdmi *hdmi, unsigned long pixel_clk,
+                               unsigned long sample_rate)
+{
+       int n;
+
+       n = hdmi_match_tmds_n_table(hdmi, pixel_clk, sample_rate);
+       if (n > 0)
+               return n;
+
+       dev_warn(hdmi->dev, "Rate %lu missing; compute N dynamically\n",
+                pixel_clk);
+
+       return hdmi_compute_n(hdmi, pixel_clk, sample_rate);
 }
 
 static void hdmi_set_clk_regenerator(struct dw_hdmi *hdmi,
@@ -280,7 +393,7 @@ static void hdmi_set_clk_regenerator(struct dw_hdmi *hdmi,
        unsigned int n, cts;
        u64 tmp;
 
-       n = hdmi_compute_n(sample_rate, pixel_clk);
+       n = hdmi_find_n(hdmi, pixel_clk, sample_rate);
 
        /*
         * Compute the CTS value from the N value.  Note that CTS and N

diff --git a/include/drm/bridge/dw_hdmi.h b/include/drm/bridge/dw_hdmi.h
index 26c06d5be23ded92d428545ed437916e622e5ee9..2fb760eb9797d8676db20969988ddfe2757a8a80 100644 (file)
--- a/include/drm/bridge/dw_hdmi.h
+++ b/include/drm/bridge/dw_hdmi.h
@@ -28,6 +28,13 @@ enum dw_hdmi_devtype {
        RK3399_HDMI,
 };
 
+struct dw_hdmi_audio_tmds_n {
+       unsigned long tmds;
+       unsigned int n_32k;
+       unsigned int n_44k1;
+       unsigned int n_48k;
+};
+
 struct dw_hdmi_mpll_config {
        unsigned long mpixelclock;
        struct {
@@ -50,6 +57,7 @@ struct dw_hdmi_phy_config {
 
 struct dw_hdmi_plat_data {
        enum dw_hdmi_devtype dev_type;
+       const struct dw_hdmi_audio_tmds_n *tmds_n_table;
        const struct dw_hdmi_mpll_config *mpll_cfg;
        const struct dw_hdmi_curr_ctrl *cur_ctr;
        const struct dw_hdmi_phy_config *phy_config;