On Tue, 2016-11-29 at 22:58 +0200, Ville Syrjälä wrote: > On Thu, Nov 17, 2016 at 06:03:47PM -0800, Dhinakaran Pandiyan wrote: > > The total or the nominal link bandwidth, which we save in terms of PBN, is > > a factor of link rate and lane count. But, currently we hardcode it to > > 2560 PBN. This results in incorrect computation of total slots. > > > > E.g, 2 lane HBR2 configuration and 4k at 60Hz, 24bpp mode > > nominal link bw = 1080 MBps = 1280PBN = 64 slots > > required bw 533.25 MHz*3 = 1599.75 MBps or 1896 PBN > > with +0.6% margin = 1907.376 PBN = 96 slots > > This is greater than the max. possible value of 64 slots. But, we > > incorrectly compute available slots as 2560 PBN = 128 slots and don't > > return error. > > > > So, let's fix this by calculating the total link bandwidth as > > link bw (PBN) = BW per time slot(PBN) * max. time slots , where max. time > > slots is 64 > > > > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com> > > --- > > drivers/gpu/drm/drm_dp_mst_topology.c | 5 ++--- > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c > > b/drivers/gpu/drm/drm_dp_mst_topology.c > > index 04e4571..26dfd99 100644 > > --- a/drivers/gpu/drm/drm_dp_mst_topology.c > > +++ b/drivers/gpu/drm/drm_dp_mst_topology.c > > @@ -2038,9 +2038,8 @@ int drm_dp_mst_topology_mgr_set_mst(struct > > drm_dp_mst_topology_mgr *mgr, bool ms > > ret = -EINVAL; > > goto out_unlock; > > } > > - > > - mgr->total_pbn = 2560; > > - mgr->total_slots = DIV_ROUND_UP(mgr->total_pbn, mgr->pbn_div); > > + mgr->total_pbn = 64 * mgr->pbn_div; > > Do we actually have a use in mind for total_pbn? It seems unused now.
Not really, I will remove it and submit this patch separately. > > > + mgr->total_slots = 64; > > Same for total_slots. > > > mgr->avail_slots = mgr->total_slots; > > So avail_slots is all that's used. And shouldn't it actually start > out at 63 instead of 64 on account of the MTP header always taking > up one slot? > Yeah, I had a check for < avail_slots in the patch that followed. -DK > > > > /* add initial branch device at LCT 1 */ > > -- > > 2.7.4 >
