Re: [PATCH v2 01/11] drm/dp_mst: Store the MST PBN divider value in fixed point format

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Nov 16, 2023 at 03:18:31PM +0200, Imre Deak wrote:
> 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 <lyude@redhat.com>
> Cc: Harry Wentland <harry.wentland@amd.com>
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Cc: Wayne Lin <wayne.lin@amd.com>
> Cc: amd-gfx@lists.freedesktop.org
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  5 +++--
>  .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c |  3 ++-
>  .../display/amdgpu_dm/amdgpu_dm_mst_types.c   |  5 +++--
>  drivers/gpu/drm/display/drm_dp_mst_topology.c | 22 +++++++++++++------
>  drivers/gpu/drm/i915/display/intel_dp_mst.c   |  3 ++-
>  drivers/gpu/drm/nouveau/dispnv50/disp.c       |  6 +++--
>  include/drm/display/drm_dp_mst_helper.h       |  7 +++---
>  7 files changed, 33 insertions(+), 18 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 74f9f02abcdec..12346b21d0b05 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_eld.h>
> @@ -6909,8 +6910,8 @@ 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));

Why doesn't that dfixed stuff return the correct type?

Anyways looks mostly mechanical
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  
>  	if (!state->duplicated) {
>  		int max_bpc = conn_state->max_requested_bpc;
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> index ed784cf27d396..63024393b516e 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c
> @@ -31,6 +31,7 @@
>  #include <drm/drm_probe_helper.h>
>  #include <drm/amdgpu_drm.h>
>  #include <drm/drm_edid.h>
> +#include <drm/drm_fixed.h>
>  
>  #include "dm_services.h"
>  #include "amdgpu.h"
> @@ -210,7 +211,7 @@ static void dm_helpers_construct_old_payload(
>  			struct drm_dp_mst_atomic_payload *old_payload)
>  {
>  	struct drm_dp_mst_atomic_payload *pos;
> -	int pbn_per_slot = mst_state->pbn_div;
> +	int pbn_per_slot = dfixed_trunc(mst_state->pbn_div);
>  	u8 next_payload_vc_start = mgr->next_start_slot;
>  	u8 payload_vc_start = new_payload->vc_start_slot;
>  	u8 allocated_time_slots;
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> index 9a58e1a4c5f49..d1ba3ae228b08 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
> @@ -27,6 +27,7 @@
>  #include <drm/display/drm_dp_mst_helper.h>
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
> +#include <drm/drm_fixed.h>
>  #include "dm_services.h"
>  #include "amdgpu.h"
>  #include "amdgpu_dm.h"
> @@ -941,10 +942,10 @@ static int increase_dsc_bpp(struct drm_atomic_state *state,
>  		link_timeslots_used = 0;
>  
>  		for (i = 0; i < count; i++)
> -			link_timeslots_used += DIV_ROUND_UP(vars[i + k].pbn, mst_state->pbn_div);
> +			link_timeslots_used += DIV_ROUND_UP(vars[i + k].pbn, dfixed_trunc(mst_state->pbn_div));
>  
>  		fair_pbn_alloc =
> -			(63 - link_timeslots_used) / remaining_to_increase * mst_state->pbn_div;
> +			(63 - link_timeslots_used) / remaining_to_increase * dfixed_trunc(mst_state->pbn_div);
>  
>  		if (initial_slack[next_index] > fair_pbn_alloc) {
>  			vars[next_index].pbn += fair_pbn_alloc;
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 4d72c9a32026e..000d05e80352a 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -43,6 +43,7 @@
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_drv.h>
>  #include <drm/drm_edid.h>
> +#include <drm/drm_fixed.h>
>  #include <drm/drm_print.h>
>  #include <drm/drm_probe_helper.h>
>  
> @@ -3578,16 +3579,22 @@ static int drm_dp_send_up_ack_reply(struct drm_dp_mst_topology_mgr *mgr,
>   * value is in units of PBNs/(timeslots/1 MTP). This value can be used to
>   * convert the number of PBNs required for a given stream to the number of
>   * timeslots this stream requires in each MTP.
> + *
> + * Returns the BW / timeslot value in 20.12 fixed point format.
>   */
> -int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
> -			     int link_rate, int link_lane_count)
> +fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
> +				    int link_rate, int link_lane_count)
>  {
> +	fixed20_12 ret;
> +
>  	if (link_rate == 0 || link_lane_count == 0)
>  		drm_dbg_kms(mgr->dev, "invalid link rate/lane count: (%d / %d)\n",
>  			    link_rate, link_lane_count);
>  
>  	/* See DP v2.0 2.6.4.2, VCPayload_Bandwidth_for_OneTimeSlotPer_MTP_Allocation */
> -	return link_rate * link_lane_count / 54000;
> +	ret.full = dfixed_const(link_rate * link_lane_count / 54000);
> +
> +	return ret;
>  }
>  EXPORT_SYMBOL(drm_dp_get_vc_payload_bw);
>  
> @@ -4335,7 +4342,7 @@ int drm_dp_atomic_find_time_slots(struct drm_atomic_state *state,
>  		}
>  	}
>  
> -	req_slots = DIV_ROUND_UP(pbn, topology_state->pbn_div);
> +	req_slots = DIV_ROUND_UP(pbn, dfixed_trunc(topology_state->pbn_div));
>  
>  	drm_dbg_atomic(mgr->dev, "[CONNECTOR:%d:%s] [MST PORT:%p] TU %d -> %d\n",
>  		       port->connector->base.id, port->connector->name,
> @@ -4872,7 +4879,8 @@ void drm_dp_mst_dump_topology(struct seq_file *m,
>  	state = to_drm_dp_mst_topology_state(mgr->base.state);
>  	seq_printf(m, "\n*** Atomic state info ***\n");
>  	seq_printf(m, "payload_mask: %x, max_payloads: %d, start_slot: %u, pbn_div: %d\n",
> -		   state->payload_mask, mgr->max_payloads, state->start_slot, state->pbn_div);
> +		   state->payload_mask, mgr->max_payloads, state->start_slot,
> +		   dfixed_trunc(state->pbn_div));
>  
>  	seq_printf(m, "\n| idx | port | vcpi | slots | pbn | dsc | status |     sink name     |\n");
>  	for (i = 0; i < mgr->max_payloads; i++) {
> @@ -5330,10 +5338,10 @@ drm_dp_mst_atomic_check_payload_alloc_limits(struct drm_dp_mst_topology_mgr *mgr
>  	}
>  
>  	if (!payload_count)
> -		mst_state->pbn_div = 0;
> +		mst_state->pbn_div.full = dfixed_const(0);
>  
>  	drm_dbg_atomic(mgr->dev, "[MST MGR:%p] mst state %p TU pbn_div=%d avail=%d used=%d\n",
> -		       mgr, mst_state, mst_state->pbn_div, avail_slots,
> +		       mgr, mst_state, dfixed_trunc(mst_state->pbn_div), avail_slots,
>  		       mst_state->total_avail_slots - avail_slots);
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 0cb9405f59eaa..e5d6b811c22ef 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -26,6 +26,7 @@
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_edid.h>
> +#include <drm/drm_fixed.h>
>  #include <drm/drm_probe_helper.h>
>  
>  #include "i915_drv.h"
> @@ -202,7 +203,7 @@ static int intel_dp_mst_find_vcpi_slots_for_bpp(struct intel_encoder *encoder,
>  		 */
>  		drm_WARN_ON(&i915->drm, remote_m_n.tu < crtc_state->dp_m_n.tu);
>  		crtc_state->dp_m_n.tu = remote_m_n.tu;
> -		crtc_state->pbn = remote_m_n.tu * mst_state->pbn_div;
> +		crtc_state->pbn = remote_m_n.tu * dfixed_trunc(mst_state->pbn_div);
>  
>  		slots = drm_dp_atomic_find_time_slots(state, &intel_dp->mst_mgr,
>  						      connector->port,
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index 493fe4660f651..11fe75b68e95c 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -40,6 +40,7 @@
>  #include <drm/drm_edid.h>
>  #include <drm/drm_eld.h>
>  #include <drm/drm_fb_helper.h>
> +#include <drm/drm_fixed.h>
>  #include <drm/drm_probe_helper.h>
>  #include <drm/drm_vblank.h>
>  
> @@ -946,7 +947,8 @@ nv50_msto_prepare(struct drm_atomic_state *state,
>  	if (ret == 0) {
>  		nvif_outp_dp_mst_vcpi(&mstm->outp->outp, msto->head->base.index,
>  				      payload->vc_start_slot, payload->time_slots,
> -				      payload->pbn, payload->time_slots * mst_state->pbn_div);
> +				      payload->pbn,
> +				      payload->time_slots * dfixed_trunc(mst_state->pbn_div));
>  	} else {
>  		nvif_outp_dp_mst_vcpi(&mstm->outp->outp, msto->head->base.index, 0, 0, 0, 0);
>  	}
> @@ -990,7 +992,7 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
>  	if (IS_ERR(mst_state))
>  		return PTR_ERR(mst_state);
>  
> -	if (!mst_state->pbn_div) {
> +	if (!mst_state->pbn_div.full) {
>  		struct nouveau_encoder *outp = mstc->mstm->outp;
>  
>  		mst_state->pbn_div = drm_dp_get_vc_payload_bw(&mstm->mgr,
> diff --git a/include/drm/display/drm_dp_mst_helper.h b/include/drm/display/drm_dp_mst_helper.h
> index a4aad6df71f18..9b19d8bd520af 100644
> --- a/include/drm/display/drm_dp_mst_helper.h
> +++ b/include/drm/display/drm_dp_mst_helper.h
> @@ -25,6 +25,7 @@
>  #include <linux/types.h>
>  #include <drm/display/drm_dp_helper.h>
>  #include <drm/drm_atomic.h>
> +#include <drm/drm_fixed.h>
>  
>  #if IS_ENABLED(CONFIG_DRM_DEBUG_DP_MST_TOPOLOGY_REFS)
>  #include <linux/stackdepot.h>
> @@ -617,7 +618,7 @@ struct drm_dp_mst_topology_state {
>  	 * @pbn_div: The current PBN divisor for this topology. The driver is expected to fill this
>  	 * out itself.
>  	 */
> -	int pbn_div;
> +	fixed20_12 pbn_div;
>  };
>  
>  #define to_dp_mst_topology_mgr(x) container_of(x, struct drm_dp_mst_topology_mgr, base)
> @@ -839,8 +840,8 @@ struct edid *drm_dp_mst_get_edid(struct drm_connector *connector,
>  				 struct drm_dp_mst_topology_mgr *mgr,
>  				 struct drm_dp_mst_port *port);
>  
> -int drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
> -			     int link_rate, int link_lane_count);
> +fixed20_12 drm_dp_get_vc_payload_bw(const struct drm_dp_mst_topology_mgr *mgr,
> +				    int link_rate, int link_lane_count);
>  
>  int drm_dp_calc_pbn_mode(int clock, int bpp);
>  
> -- 
> 2.39.2

-- 
Ville Syrjälä
Intel