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.
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@xxxxxxx>
Signed-off-by: David Francis <David.Francis@xxxxxxx>
---
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 398e7314ea8b..34a5bdfc598b 100644
--- a/drivers/gpu/drm/drm_dp_mst_topology.c
+++ b/drivers/gpu/drm/drm_dp_mst_topology.c
@@ -3588,6 +3588,49 @@ 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
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