Re: [PATCH v8 1/6] drm/dp_mst: Add PBN calculation for DSC modes

[Harry Wentland <hwentlan@amd.com>]

On 2019-08-26 2:05 p.m., David Francis wrote:
> With DSC, bpp can be fractional in multiples of 1/16.
> 
> Change drm_dp_calc_pbn_mode to reflect this, adding a new
> parameter bool dsc. When this parameter is true, treat the
> bpp parameter as having units not of bits per pixel, but
> 1/16 of a bit per pixel
> 
> v2: Don't add separate function for this
> 
> Cc: amd-gfx@lists.freedesktop.org
> Cc: nouveau@lists.freedesktop.org
> Cc: intel-gfx@lists.freedesktop.org
> Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
> Reviewed-by: Lyude Paul <lyude@redhat.com>

Reviewed-by: Harry Wentland <harry.wentland@amd.com>

Harry

> Signed-off-by: David Francis <David.Francis@amd.com>
> ---
>  .../amd/display/amdgpu_dm/amdgpu_dm_helpers.c    |  2 +-
>  drivers/gpu/drm/drm_dp_mst_topology.c            | 16 ++++++++++++----
>  drivers/gpu/drm/i915/display/intel_dp_mst.c      |  2 +-
>  drivers/gpu/drm/nouveau/dispnv50/disp.c          |  2 +-
>  drivers/gpu/drm/radeon/radeon_dp_mst.c           |  2 +-
>  include/drm/drm_dp_mst_helper.h                  |  3 +--
>  6 files changed, 17 insertions(+), 10 deletions(-)
> 
> 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 a0ed0154a9f0..abafb5221b44 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
> @@ -235,7 +235,7 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
>  
>  		/* TODO need to know link rate */
>  
> -		pbn = drm_dp_calc_pbn_mode(clock, bpp);
> +		pbn = drm_dp_calc_pbn_mode(clock, bpp, false);
>  
>  		slots = drm_dp_find_vcpi_slots(mst_mgr, pbn);
>  		ret = drm_dp_mst_allocate_vcpi(mst_mgr, mst_port, pbn, slots);
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 82add736e17d..3e7b7553cf4d 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3534,10 +3534,11 @@ EXPORT_SYMBOL(drm_dp_check_act_status);
>   * drm_dp_calc_pbn_mode() - Calculate the PBN for a mode.
>   * @clock: dot clock for the mode
>   * @bpp: bpp for the mode.
> + * @dsc: DSC mode. If true, bpp has units of 1/16 of a bit per pixel
>   *
>   * This uses the formula in the spec to calculate the PBN value for a mode.
>   */
> -int drm_dp_calc_pbn_mode(int clock, int bpp)
> +int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc)
>  {
>  	u64 kbps;
>  	s64 peak_kbps;
> @@ -3555,11 +3556,18 @@ int drm_dp_calc_pbn_mode(int clock, int bpp)
>  	 * peak_kbps *= (1006/1000)
>  	 * peak_kbps *= (64/54)
>  	 * peak_kbps *= 8    convert to bytes
> +	 *
> +	 * If the bpp is in units of 1/16, further divide by 16. Put this
> +	 * factor in the numerator rather than the denominator to avoid
> +	 * integer overflow
>  	 */
>  
>  	numerator = 64 * 1006;
>  	denominator = 54 * 8 * 1000 * 1000;
>  
> +	if (dsc)
> +		numerator /= 16;
> +
>  	kbps *= numerator;
>  	peak_kbps = drm_fixp_from_fraction(kbps, denominator);
>  
> @@ -3570,19 +3578,19 @@ EXPORT_SYMBOL(drm_dp_calc_pbn_mode);
>  static int test_calc_pbn_mode(void)
>  {
>  	int ret;
> -	ret = drm_dp_calc_pbn_mode(154000, 30);
> +	ret = drm_dp_calc_pbn_mode(154000, 30, false);
>  	if (ret != 689) {
>  		DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
>  				154000, 30, 689, ret);
>  		return -EINVAL;
>  	}
> -	ret = drm_dp_calc_pbn_mode(234000, 30);
> +	ret = drm_dp_calc_pbn_mode(234000, 30, false);
>  	if (ret != 1047) {
>  		DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
>  				234000, 30, 1047, ret);
>  		return -EINVAL;
>  	}
> -	ret = drm_dp_calc_pbn_mode(297000, 24);
> +	ret = drm_dp_calc_pbn_mode(297000, 24, false);
>  	if (ret != 1063) {
>  		DRM_ERROR("PBN calculation test failed - clock %d, bpp %d, expected PBN %d, actual PBN %d.\n",
>  				297000, 24, 1063, ret);
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> index 2c5ac3dd647f..4f17f61f4453 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> @@ -61,7 +61,7 @@ static int intel_dp_mst_compute_link_config(struct intel_encoder *encoder,
>  		crtc_state->pipe_bpp = bpp;
>  
>  		crtc_state->pbn = drm_dp_calc_pbn_mode(adjusted_mode->crtc_clock,
> -						       crtc_state->pipe_bpp);
> +						       crtc_state->pipe_bpp, false);
>  
>  		slots = drm_dp_atomic_find_vcpi_slots(state, &intel_dp->mst_mgr,
>  						      port, crtc_state->pbn);
> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> index 5c36c75232e6..c68783c1f3fa 100644
> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
> @@ -782,7 +782,7 @@ nv50_msto_atomic_check(struct drm_encoder *encoder,
>  			const int bpp = connector->display_info.bpc * 3;
>  			const int clock = crtc_state->adjusted_mode.clock;
>  
> -			asyh->dp.pbn = drm_dp_calc_pbn_mode(clock, bpp);
> +			asyh->dp.pbn = drm_dp_calc_pbn_mode(clock, bpp, false);
>  		}
>  
>  		slots = drm_dp_atomic_find_vcpi_slots(state, &mstm->mgr,
> diff --git a/drivers/gpu/drm/radeon/radeon_dp_mst.c b/drivers/gpu/drm/radeon/radeon_dp_mst.c
> index 2994f07fbad9..c997f88218f2 100644
> --- a/drivers/gpu/drm/radeon/radeon_dp_mst.c
> +++ b/drivers/gpu/drm/radeon/radeon_dp_mst.c
> @@ -514,7 +514,7 @@ static bool radeon_mst_mode_fixup(struct drm_encoder *encoder,
>  
>  	mst_enc = radeon_encoder->enc_priv;
>  
> -	mst_enc->pbn = drm_dp_calc_pbn_mode(adjusted_mode->clock, bpp);
> +	mst_enc->pbn = drm_dp_calc_pbn_mode(adjusted_mode->clock, bpp, false);
>  
>  	mst_enc->primary->active_device = mst_enc->primary->devices & mst_enc->connector->devices;
>  	DRM_DEBUG_KMS("setting active device to %08x from %08x %08x for encoder %d\n",
> diff --git a/include/drm/drm_dp_mst_helper.h b/include/drm/drm_dp_mst_helper.h
> index 2ba6253ea6d3..9116b2c95239 100644
> --- a/include/drm/drm_dp_mst_helper.h
> +++ b/include/drm/drm_dp_mst_helper.h
> @@ -610,8 +610,7 @@ bool drm_dp_mst_port_has_audio(struct drm_dp_mst_topology_mgr *mgr,
>  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_calc_pbn_mode(int clock, int bpp);
> -
> +int drm_dp_calc_pbn_mode(int clock, int bpp, bool dsc);
>  
>  bool drm_dp_mst_allocate_vcpi(struct drm_dp_mst_topology_mgr *mgr,
>  			      struct drm_dp_mst_port *port, int pbn, int slots);
> 
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