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    SubjectRe: [PATCH 1/2] drm/amdgpu/mst: Stop ignoring error codes and deadlocking
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    On Wed, 2022-11-09 at 09:48 +0000, Lin, Wayne wrote:
    > [Public]
    >
    > Thanks, Lyude!
    > Comments inline.
    >
    > > -----Original Message-----
    > > From: Lyude Paul <lyude@redhat.com>
    > > Sent: Saturday, November 5, 2022 7:59 AM
    > > To: amd-gfx@lists.freedesktop.org
    > > Cc: Wentland, Harry <Harry.Wentland@amd.com>; stable@vger.kernel.org;
    > > Li, Sun peng (Leo) <Sunpeng.Li@amd.com>; Siqueira, Rodrigo
    > > <Rodrigo.Siqueira@amd.com>; Deucher, Alexander
    > > <Alexander.Deucher@amd.com>; Koenig, Christian
    > > <Christian.Koenig@amd.com>; Pan, Xinhui <Xinhui.Pan@amd.com>; David
    > > Airlie <airlied@gmail.com>; Daniel Vetter <daniel@ffwll.ch>; Kazlauskas,
    > > Nicholas <Nicholas.Kazlauskas@amd.com>; Pillai, Aurabindo
    > > <Aurabindo.Pillai@amd.com>; Li, Roman <Roman.Li@amd.com>; Zuo, Jerry
    > > <Jerry.Zuo@amd.com>; Wu, Hersen <hersenxs.wu@amd.com>; Lin, Wayne
    > > <Wayne.Lin@amd.com>; Thomas Zimmermann <tzimmermann@suse.de>;
    > > Mahfooz, Hamza <Hamza.Mahfooz@amd.com>; Hung, Alex
    > > <Alex.Hung@amd.com>; Francis, David <David.Francis@amd.com>; Mikita
    > > Lipski <mikita.lipski@amd.com>; Liu, Wenjing <Wenjing.Liu@amd.com>;
    > > open list:DRM DRIVERS <dri-devel@lists.freedesktop.org>; open list <linux-
    > > kernel@vger.kernel.org>
    > > 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@redhat.com>
    > > Fixes: 8c20a1ed9b4f ("drm/amd/display: MST DSC compute fair share")
    > > Cc: Harry Wentland <harry.wentland@amd.com>
    > > Cc: <stable@vger.kernel.org> # 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?

    Yes we should, nice catch!

    >
    > > }
    > > - 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.

    sgtm


    >
    > > }
    > >
    > > /* 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
    >

    --
    Cheers,
    Lyude Paul (she/her)
    Software Engineer at Red Hat

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