RE: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and deadlocking

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Thanks, Lyude!
Comments inline.

> -----Original Message-----
> From: Lyude Paul <lyude@xxxxxxxxxx>
> Sent: Saturday, November 5, 2022 7:59 AM
> To: amd-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: Wentland, Harry <Harry.Wentland@xxxxxxx>; stable@xxxxxxxxxxxxxxx;
> Li, Sun peng (Leo) <Sunpeng.Li@xxxxxxx>; Siqueira, Rodrigo
> <Rodrigo.Siqueira@xxxxxxx>; Deucher, Alexander
> <Alexander.Deucher@xxxxxxx>; Koenig, Christian
> <Christian.Koenig@xxxxxxx>; Pan, Xinhui <Xinhui.Pan@xxxxxxx>; David
> Airlie <airlied@xxxxxxxxx>; Daniel Vetter <daniel@xxxxxxxx>; Kazlauskas,
> Nicholas <Nicholas.Kazlauskas@xxxxxxx>; Pillai, Aurabindo
> <Aurabindo.Pillai@xxxxxxx>; Li, Roman <Roman.Li@xxxxxxx>; Zuo, Jerry
> <Jerry.Zuo@xxxxxxx>; Wu, Hersen <hersenxs.wu@xxxxxxx>; Lin, Wayne
> <Wayne.Lin@xxxxxxx>; Thomas Zimmermann <tzimmermann@xxxxxxx>;
> Mahfooz, Hamza <Hamza.Mahfooz@xxxxxxx>; Hung, Alex
> <Alex.Hung@xxxxxxx>; Francis, David <David.Francis@xxxxxxx>; Mikita
> Lipski <mikita.lipski@xxxxxxx>; Liu, Wenjing <Wenjing.Liu@xxxxxxx>;
> open list:DRM DRIVERS <dri-devel@xxxxxxxxxxxxxxxxxxxxx>; open list <linux-
> kernel@xxxxxxxxxxxxxxx>
> Subject: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and
> deadlocking
> 
> It appears that amdgpu makes the mistake of completely ignoring the return
> values from the DP MST helpers, and instead just returns a simple true/false.
> In this case, it seems to have come back to bite us because as a result of
> simply returning false from compute_mst_dsc_configs_for_state(), amdgpu
> had no way of telling when a deadlock happened from these helpers. This
> could definitely result in some kernel splats.
> 
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Fixes: 8c20a1ed9b4f ("drm/amd/display: MST DSC compute fair share")
> Cc: Harry Wentland <harry.wentland@xxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v5.6+
> ---
>  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  18 +--
>  .../display/amdgpu_dm/amdgpu_dm_mst_types.c   | 107 ++++++++++------
> --
>  .../display/amdgpu_dm/amdgpu_dm_mst_types.h   |  12 +-
>  3 files changed, 73 insertions(+), 64 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 0db2a88cd4d7b..6f76b2c84cdb5 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -6462,7 +6462,7 @@ static int
> dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
>  	struct drm_connector_state *new_con_state;
>  	struct amdgpu_dm_connector *aconnector;
>  	struct dm_connector_state *dm_conn_state;
> -	int i, j;
> +	int i, j, ret;
>  	int vcpi, pbn_div, pbn, slot_num = 0;
> 
>  	for_each_new_connector_in_state(state, connector,
> new_con_state, i) { @@ -6509,8 +6509,11 @@ static int
> dm_update_mst_vcpi_slots_for_dsc(struct drm_atomic_state *state,
>  			dm_conn_state->pbn = pbn;
>  			dm_conn_state->vcpi_slots = slot_num;
> 
> -			drm_dp_mst_atomic_enable_dsc(state, aconnector-
> >port, dm_conn_state->pbn,
> -						     false);
> +			ret = drm_dp_mst_atomic_enable_dsc(state,
> aconnector->port,
> +							   dm_conn_state-
> >pbn, false);
> +			if (ret != 0)
> +				return ret;
> +
>  			continue;
>  		}
> 
> @@ -9523,10 +9526,9 @@ static int amdgpu_dm_atomic_check(struct
> drm_device *dev,
> 
>  #if defined(CONFIG_DRM_AMD_DC_DCN)
>  	if (dc_resource_is_dsc_encoding_supported(dc)) {
> -		if (!pre_validate_dsc(state, &dm_state, vars)) {
> -			ret = -EINVAL;
> +		ret = pre_validate_dsc(state, &dm_state, vars);
> +		if (ret != 0)
>  			goto fail;
> -		}
>  	}
>  #endif
> 
> @@ -9621,9 +9623,9 @@ static int amdgpu_dm_atomic_check(struct
> drm_device *dev,
>  		}
> 
>  #if defined(CONFIG_DRM_AMD_DC_DCN)
> -		if (!compute_mst_dsc_configs_for_state(state, dm_state-
> >context, vars)) {
> +		ret = compute_mst_dsc_configs_for_state(state, dm_state-
> >context, vars);
> +		if (ret) {
> 
> 	DRM_DEBUG_DRIVER("compute_mst_dsc_configs_for_state()
> failed\n");
> -			ret = -EINVAL;
>  			goto fail;
>  		}
> 
> 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 6ff96b4bdda5c..30bc2e5058b70 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
> @@ -864,25 +864,25 @@ static bool try_disable_dsc(struct
> drm_atomic_state *state,
>  	return true;
>  }
> 
> -static bool compute_mst_dsc_configs_for_link(struct drm_atomic_state
> *state,
> -					     struct dc_state *dc_state,
> -					     struct dc_link *dc_link,
> -					     struct dsc_mst_fairness_vars *vars,
> -					     struct drm_dp_mst_topology_mgr
> *mgr,
> -					     int *link_vars_start_index)
> +static int compute_mst_dsc_configs_for_link(struct drm_atomic_state
> *state,
> +					    struct dc_state *dc_state,
> +					    struct dc_link *dc_link,
> +					    struct dsc_mst_fairness_vars *vars,
> +					    struct drm_dp_mst_topology_mgr
> *mgr,
> +					    int *link_vars_start_index)
>  {
>  	struct dc_stream_state *stream;
>  	struct dsc_mst_fairness_params params[MAX_PIPES];
>  	struct amdgpu_dm_connector *aconnector;
>  	struct drm_dp_mst_topology_state *mst_state =
> drm_atomic_get_mst_topology_state(state, mgr);
>  	int count = 0;
> -	int i, k;
> +	int i, k, ret;
>  	bool debugfs_overwrite = false;
> 
>  	memset(params, 0, sizeof(params));
> 
>  	if (IS_ERR(mst_state))
> -		return false;
> +		return PTR_ERR(mst_state);
> 
>  	mst_state->pbn_div = dm_mst_get_pbn_divider(dc_link);  #if
> defined(CONFIG_DRM_AMD_DC_DCN) @@ -933,7 +933,7 @@ static bool
> compute_mst_dsc_configs_for_link(struct drm_atomic_state *state,
> 
>  	if (count == 0) {
>  		ASSERT(0);
> -		return true;
> +		return 0;
>  	}
> 
>  	/* k is start index of vars for current phy link used by mst hub */ @@
> -949,11 +949,14 @@ static bool compute_mst_dsc_configs_for_link(struct
> drm_atomic_state *state,
>  		vars[i + k].bpp_x16 = 0;
>  		if (drm_dp_atomic_find_time_slots(state, params[i].port-
> >mgr, params[i].port,
>  						  vars[i + k].pbn) < 0)
> -			return false;
> +			return -EINVAL;

Should we also return the error code get from drm_dp_atomic_find_time_slots() rather than 
assigning a new one here?

>  	}
> -	if (!drm_dp_mst_atomic_check(state) && !debugfs_overwrite) {
> +	ret = drm_dp_mst_atomic_check(state);
> +	if (ret == 0 && !debugfs_overwrite) {
>  		set_dsc_configs_from_fairness_vars(params, vars, count, k);
> -		return true;
> +		return 0;
> +	} else if (ret == -EDEADLK) {
> +		return ret;

I think we should return here whenever there is an error. Not just for EDEADLK case. 

>  	}
> 
>  	/* Try max compression */
> @@ -964,29 +967,30 @@ static bool
> compute_mst_dsc_configs_for_link(struct drm_atomic_state *state,
>  			vars[i + k].bpp_x16 =
> params[i].bw_range.min_target_bpp_x16;
>  			if (drm_dp_atomic_find_time_slots(state,
> params[i].port->mgr,
>  							  params[i].port, vars[i
> + k].pbn) < 0)
> -				return false;
> +				return -EINVAL;

Same as above.

>  		} else {
>  			vars[i + k].pbn =
> kbps_to_peak_pbn(params[i].bw_range.stream_kbps);
>  			vars[i + k].dsc_enabled = false;
>  			vars[i + k].bpp_x16 = 0;
>  			if (drm_dp_atomic_find_time_slots(state,
> params[i].port->mgr,
>  							  params[i].port, vars[i
> + k].pbn) < 0)
> -				return false;
> +				return -EINVAL;

Same as above.

>  		}
>  	}
> -	if (drm_dp_mst_atomic_check(state))
> -		return false;
> +	ret = drm_dp_mst_atomic_check(state);
> +	if (ret != 0)
> +		return ret;
> 
>  	/* Optimize degree of compression */
>  	if (!increase_dsc_bpp(state, mst_state, dc_link, params, vars, count,
> k))
> -		return false;
> +		return -ENOSPC;
> 
>  	if (!try_disable_dsc(state, dc_link, params, vars, count, k))
> -		return false;
> +		return -ENOSPC;
> 
>  	set_dsc_configs_from_fairness_vars(params, vars, count, k);
> 
> -	return true;
> +	return 0;
>  }
> 
>  static bool is_dsc_need_re_compute(
> @@ -1087,15 +1091,16 @@ static bool is_dsc_need_re_compute(
>  	return is_dsc_need_re_compute;
>  }
> 
> -bool compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> -				       struct dc_state *dc_state,
> -				       struct dsc_mst_fairness_vars *vars)
> +int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> +				      struct dc_state *dc_state,
> +				      struct dsc_mst_fairness_vars *vars)
>  {
>  	int i, j;
>  	struct dc_stream_state *stream;
>  	bool computed_streams[MAX_PIPES];
>  	struct amdgpu_dm_connector *aconnector;
>  	int link_vars_start_index = 0;
> +	int ret = 0;
> 
>  	for (i = 0; i < dc_state->stream_count; i++)
>  		computed_streams[i] = false;
> @@ -1118,17 +1123,19 @@ bool compute_mst_dsc_configs_for_state(struct
> drm_atomic_state *state,
>  			continue;
> 
>  		if (dcn20_remove_stream_from_ctx(stream->ctx->dc,
> dc_state, stream) != DC_OK)
> -			return false;
> +			return -EINVAL;
> 
>  		if (!is_dsc_need_re_compute(state, dc_state, stream->link))
>  			continue;
> 
>  		mutex_lock(&aconnector->mst_mgr.lock);
> -		if (!compute_mst_dsc_configs_for_link(state, dc_state,
> stream->link, vars,
> -						      &aconnector->mst_mgr,
> -						      &link_vars_start_index)) {
> +
> +		ret = compute_mst_dsc_configs_for_link(state, dc_state,
> stream->link, vars,
> +						       &aconnector->mst_mgr,
> +						       &link_vars_start_index);
> +		if (ret != 0) {
>  			mutex_unlock(&aconnector->mst_mgr.lock);
> -			return false;
> +			return ret;
>  		}
>  		mutex_unlock(&aconnector->mst_mgr.lock);
> 
> @@ -1143,22 +1150,22 @@ bool compute_mst_dsc_configs_for_state(struct
> drm_atomic_state *state,
> 
>  		if (stream->timing.flags.DSC == 1)
>  			if (dc_stream_add_dsc_to_resource(stream->ctx-
> >dc, dc_state, stream) != DC_OK)
> -				return false;
> +				return -EINVAL;
>  	}
> 
> -	return true;
> +	return ret;
>  }
> 
> -static bool
> -	pre_compute_mst_dsc_configs_for_state(struct drm_atomic_state
> *state,
> -					      struct dc_state *dc_state,
> -					      struct dsc_mst_fairness_vars
> *vars)
> +static int pre_compute_mst_dsc_configs_for_state(struct
> drm_atomic_state *state,
> +						 struct dc_state *dc_state,
> +						 struct dsc_mst_fairness_vars
> *vars)
>  {
>  	int i, j;
>  	struct dc_stream_state *stream;
>  	bool computed_streams[MAX_PIPES];
>  	struct amdgpu_dm_connector *aconnector;
>  	int link_vars_start_index = 0;
> +	int ret;
> 
>  	for (i = 0; i < dc_state->stream_count; i++)
>  		computed_streams[i] = false;
> @@ -1184,13 +1191,12 @@ static bool
>  			continue;
> 
>  		mutex_lock(&aconnector->mst_mgr.lock);
> -		if (!compute_mst_dsc_configs_for_link(state, dc_state,
> stream->link, vars,
> -						      &aconnector->mst_mgr,
> -						      &link_vars_start_index)) {
> -			mutex_unlock(&aconnector->mst_mgr.lock);
> -			return false;
> -		}
> +		ret = compute_mst_dsc_configs_for_link(state, dc_state,
> stream->link, vars,
> +						       &aconnector->mst_mgr,
> +						       &link_vars_start_index);
>  		mutex_unlock(&aconnector->mst_mgr.lock);
> +		if (ret != 0)
> +			return ret;
> 
>  		for (j = 0; j < dc_state->stream_count; j++) {
>  			if (dc_state->streams[j]->link == stream->link) @@ -
> 1198,7 +1204,7 @@ static bool
>  		}
>  	}
> 
> -	return true;
> +	return ret;
>  }
> 
>  static int find_crtc_index_in_state_by_stream(struct drm_atomic_state
> *state, @@ -1253,9 +1259,9 @@ static bool
> is_dsc_precompute_needed(struct drm_atomic_state *state)
>  	return ret;
>  }
> 
> -bool pre_validate_dsc(struct drm_atomic_state *state,
> -		      struct dm_atomic_state **dm_state_ptr,
> -		      struct dsc_mst_fairness_vars *vars)
> +int pre_validate_dsc(struct drm_atomic_state *state,
> +		     struct dm_atomic_state **dm_state_ptr,
> +		     struct dsc_mst_fairness_vars *vars)
>  {
>  	int i;
>  	struct dm_atomic_state *dm_state;
> @@ -1264,11 +1270,12 @@ bool pre_validate_dsc(struct drm_atomic_state
> *state,
> 
>  	if (!is_dsc_precompute_needed(state)) {
>  		DRM_INFO_ONCE("DSC precompute is not needed.\n");
> -		return true;
> +		return 0;
>  	}
> -	if (dm_atomic_get_state(state, dm_state_ptr)) {
> +	ret = dm_atomic_get_state(state, dm_state_ptr);
> +	if (ret != 0) {
>  		DRM_INFO_ONCE("dm_atomic_get_state() failed\n");
> -		return false;
> +		return ret;
>  	}
>  	dm_state = *dm_state_ptr;
> 
> @@ -1280,7 +1287,7 @@ bool pre_validate_dsc(struct drm_atomic_state
> *state,
> 
>  	local_dc_state = kmemdup(dm_state->context, sizeof(struct
> dc_state), GFP_KERNEL);
>  	if (!local_dc_state)
> -		return false;
> +		return -ENOMEM;
> 
>  	for (i = 0; i < local_dc_state->stream_count; i++) {
>  		struct dc_stream_state *stream = dm_state->context-
> >streams[i]; @@ -1316,9 +1323,9 @@ bool pre_validate_dsc(struct
> drm_atomic_state *state,
>  	if (ret != 0)
>  		goto clean_exit;
> 
> -	if (!pre_compute_mst_dsc_configs_for_state(state, local_dc_state,
> vars)) {
> +	ret = pre_compute_mst_dsc_configs_for_state(state, local_dc_state,
> vars);
> +	if (ret != 0) {
> 
> 	DRM_INFO_ONCE("pre_compute_mst_dsc_configs_for_state()
> failed\n");
> -		ret = -EINVAL;
>  		goto clean_exit;
>  	}
> 
> @@ -1349,7 +1356,7 @@ bool pre_validate_dsc(struct drm_atomic_state
> *state,
> 
>  	kfree(local_dc_state);
> 
> -	return (ret == 0);
> +	return ret;
>  }
> 
>  static unsigned int kbps_from_pbn(unsigned int pbn) diff --git
> a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> index b92a7c5671aa2..97fd70df531bf 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> +++
> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.h
> @@ -53,15 +53,15 @@ struct dsc_mst_fairness_vars {
>  	struct amdgpu_dm_connector *aconnector;  };
> 
> -bool compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> -				       struct dc_state *dc_state,
> -				       struct dsc_mst_fairness_vars *vars);
> +int compute_mst_dsc_configs_for_state(struct drm_atomic_state *state,
> +				      struct dc_state *dc_state,
> +				      struct dsc_mst_fairness_vars *vars);
> 
>  bool needs_dsc_aux_workaround(struct dc_link *link);
> 
> -bool pre_validate_dsc(struct drm_atomic_state *state,
> -		      struct dm_atomic_state **dm_state_ptr,
> -		      struct dsc_mst_fairness_vars *vars);
> +int pre_validate_dsc(struct drm_atomic_state *state,
> +		     struct dm_atomic_state **dm_state_ptr,
> +		     struct dsc_mst_fairness_vars *vars);
> 
>  enum dc_status dm_dp_mst_is_port_support_mode(
>  	struct amdgpu_dm_connector *aconnector,
> --
> 2.37.3
---
Regards,
Wayne Lin




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