[PATCH v4 1/5] drm/dp-mst: Add PBN calculation for DSC modes

[David Francis]

With DSC, bpp can be a multiple of 1/16, so
drm_dp_calc_pbn_mode is insufficient.

Add drm_dp_calc_pbn_mode_dsc, a function which is
the same as drm_dp_calc_pbn_mode, but the bpp is
in units of 1/16.

Reviewed-by: Lyude Paul <lyude at redhat.com>
Signed-off-by: David Francis <David.Francis at amd.com>
---
 drivers/gpu/drm/drm_dp_mst_topology.c | 43 +++++++++++++++++++++++++++
 include/drm/drm_dp_mst_helper.h       |  2 +-
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
index 82add736e17d..8e2e731c35c5 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3591,6 +3591,49 @@ static int test_calc_pbn_mode(void)
 	return 0;
 }
 
+/**
+ * drm_dp_calc_pbn_mode_dsc() - Calculate the PBN for a mode with DSC enabled.
+ * @clock: dot clock for the mode
+ * @dsc_bpp: dsc bits per pixel x16 (e.g. dsc_bpp = 136 is 8.5 bpp)
+ *
+ * This uses the formula in the spec to calculate the PBN value for a mode,
+ * given that the mode is using DSC
+ * Returns:
+ * PBN required for this mode
+ */
+int drm_dp_calc_pbn_mode_dsc(int clock, int dsc_bpp)
+{
+	u64 kbps;
+	s64 peak_kbps;
+	u32 numerator;
+	u32 denominator;
+
+	kbps = clock * dsc_bpp;
+
+	/*
+	 * margin 5300ppm + 300ppm ~ 0.6% as per spec, factor is 1.006
+	 * The unit of 54/64Mbytes/sec is an arbitrary unit chosen based on
+	 * common multiplier to render an integer PBN for all link rate/lane
+	 * counts combinations
+	 * calculate
+	 * peak_kbps *= (1/16) bppx16 to bpp
+	 * peak_kbps *= (1006/1000)
+	 * peak_kbps *= (64/54)
+	 * peak_kbps *= 8    convert to bytes
+	 *
+	 * Divide numerator and denominator by 16 to avoid overflow
+	 */
+
+	numerator = 64 * 1006 / 16;
+	denominator = 54 * 8 * 1000 * 1000;
+
+	kbps *= numerator;
+	peak_kbps = drm_fixp_from_fraction(kbps, denominator);
+
+	return drm_fixp2int_ceil(peak_kbps);
+}
+EXPORT_SYMBOL(drm_dp_calc_pbn_mode_dsc);
+
 /* we want to kick the TX after we've ack the up/down IRQs. */
 static void drm_dp_mst_kick_tx(struct drm_dp_mst_topology_mgr *mgr)
 {
diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
index 2ba6253ea6d3..ddb518f2157a 100644
--- a/include/drm/drm_dp_mst_helper.h
+++ b/include/drm/drm_dp_mst_helper.h
@@ -611,7 +611,7 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector, struct drm_dp_
 
 
 int drm_dp_calc_pbn_mode(int clock, int bpp);
-
+int drm_dp_calc_pbn_mode_dsc(int clock, int dsc_bpp);
 
 bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
 			      struct drm_dp_mst_port *port, int pbn, int slots);
-- 
2.17.1