drm/dp_mst: Store the MST PBN divider value in fixed point format

On UHBR links the PBN divider is a fractional number, accordingly store
it in fixed point format. For now drm_dp_get_vc_payload_bw() always
returns a whole number and all callers will use only the integer part of
it which should preserve the current behavior. The next patch will fix
drm_dp_get_vc_payload_bw() for UHBR rates returning a fractional number
for those (also accounting for the channel coding efficiency correctly).

Cc: Lyude Paul <[email protected]>
Cc: Harry Wentland <[email protected]>
Cc: Alex Deucher <[email protected]>
Cc: Wayne Lin <[email protected]>
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Ville Syrjälä <[email protected]>
Acked-by: Daniel Vetter <[email protected]>
Acked-by: Maarten Lankhorst <[email protected]>
[Rebased changes in dm_helpers_construct_old_payload() on drm-intel-next]
Signed-off-by: Imre Deak <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index df3c42bb9274..2253e8fd2d18 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -85,6 +85,7 @@
 #include <drm/drm_atomic_uapi.h>
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_blend.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_edid.h>
 #include <drm/drm_vblank.h>
@@ -6863,8 +6864,8 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder,
 	if (IS_ERR(mst_state))
 		return PTR_ERR(mst_state);
 
-	if (!mst_state->pbn_div)
-		mst_state->pbn_div = dm_mst_get_pbn_divider(aconnector->mst_root->dc_link);
+	if (!mst_state->pbn_div.full)
+		mst_state->pbn_div.full = dfixed_const(dm_mst_get_pbn_divider(aconnector->mst_root->dc_link));
 
 	if (!state->duplicated) {
 		int max_bpc = conn_state->max_requested_bpc;