gpu: nvgpu: support binding multiple channels to a debug session

We currently bind only one channel to a debug session
But some use cases might need multiple channels bound
to same debug session

Add this support by adding a list of channels to debug session.
List structure is implemented as struct dbg_session_channel_data

List node dbg_s_list_node is currently defined in struct
dbg_session_gk20a. But this is inefficient when we need to
add debug session to multiple channels

Hence add new reference structure dbg_session_data to
store dbg_session pointer and list entry

For each NVGPU_DBG_GPU_IOCTL_BIND_CHANNEL call, create
two reference structure dbg_session_channel_data for channel
and dbg_session_data for debug session and bind them together

Define API nvgpu_dbg_gpu_get_session_channel() which will
get first channel in the list of debug session
Use this API wherever we refer to channel bound to debug
session

Remove dbg_sessions define in struct gk20a since it is
not being used anywhere

Add new API NVGPU_DBG_GPU_IOCTL_UNBIND_CHANNEL to support
unbinding of channel from debug sesssion

Bug 200156699

Change-Id: I3bfa6f9cd5b90e7254a75c7e64ac893739776b7f
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/1120331
GVS: Gerrit_Virtual_Submit
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>

5 files changed, 235 insertions, 61 deletions

diff --git a/drivers/gpu/nvgpu/gk20a/channel_gk20a.c b/drivers/gpu/nvgpu/gk20a/channel_gk20a.c
index b7bccd07..e0beefb1 100644
--- a/drivers/gpu/nvgpu/gk20a/channel_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/channel_gk20a.c
@@ -857,6 +857,8 @@ static void gk20a_free_channel(struct channel_gk20a *ch)
         struct vm_gk20a *ch_vm = ch->vm;
         unsigned long timeout = gk20a_get_gr_idle_timeout(g);
         struct dbg_session_gk20a *dbg_s;
+        struct dbg_session_data *session_data, *tmp_s;
+        struct dbg_session_channel_data *ch_data, *tmp;
         bool was_reset;
 
         gk20a_dbg_fn("");
@@ -992,14 +994,21 @@ unbind:
         WARN_ON(ch->sync);
 
         /* unlink all debug sessions */
-        mutex_lock(&ch->dbg_s_lock);
-
-        list_for_each_entry(dbg_s, &ch->dbg_s_list, dbg_s_list_node) {
-                dbg_s->ch = NULL;
-                list_del_init(&dbg_s->dbg_s_list_node);
+        mutex_lock(&g->dbg_sessions_lock);
+
+        list_for_each_entry_safe(session_data, tmp_s,
+                                &ch->dbg_s_list, dbg_s_entry) {
+                dbg_s = session_data->dbg_s;
+                mutex_lock(&dbg_s->ch_list_lock);
+                list_for_each_entry_safe(ch_data, tmp,
+                                        &dbg_s->ch_list, ch_entry) {
+                        if (ch_data->chid == ch->hw_chid)
+                                dbg_unbind_single_channel_gk20a(dbg_s, ch_data);
+                }
+                mutex_unlock(&dbg_s->ch_list_lock);
         }
 
-        mutex_unlock(&ch->dbg_s_lock);
+        mutex_unlock(&g->dbg_sessions_lock);
 
 release:
         /* make sure we catch accesses of unopened channels in case
diff --git a/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.c b/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.c
index f717e207..34685416 100644
--- a/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.c
@@ -35,6 +35,33 @@ struct dbg_gpu_session_ops dbg_gpu_session_ops_gk20a = {
         .exec_reg_ops = exec_regops_gk20a,
 };
 
+/*
+ * API to get first channel from the list of all channels
+ * bound to the debug session
+ */
+struct channel_gk20a *
+nvgpu_dbg_gpu_get_session_channel(struct dbg_session_gk20a *dbg_s)
+{
+        struct dbg_session_channel_data *ch_data;
+        struct channel_gk20a *ch;
+        struct gk20a *g = dbg_s->g;
+
+        mutex_lock(&dbg_s->ch_list_lock);
+        if (list_empty(&dbg_s->ch_list)) {
+                mutex_unlock(&dbg_s->ch_list_lock);
+                return NULL;
+        }
+
+        ch_data = list_first_entry(&dbg_s->ch_list,
+                                   struct dbg_session_channel_data,
+                                   ch_entry);
+        ch = g->fifo.channel + ch_data->chid;
+
+        mutex_unlock(&dbg_s->ch_list_lock);
+
+        return ch;
+}
+
 /* silly allocator - just increment session id */
 static atomic_t session_id = ATOMIC_INIT(0);
 static int generate_session_id(void)
@@ -95,8 +122,9 @@ static int gk20a_dbg_gpu_do_dev_open(struct inode *inode,
         if (gk20a_gpu_is_virtual(dev))
                 dbg_session->is_pg_disabled = true;
 
-        INIT_LIST_HEAD(&dbg_session->dbg_s_list_node);
         init_waitqueue_head(&dbg_session->dbg_events.wait_queue);
+        INIT_LIST_HEAD(&dbg_session->ch_list);
+        mutex_init(&dbg_session->ch_list_lock);
         dbg_session->dbg_events.events_enabled = false;
         dbg_session->dbg_events.num_pending_events = 0;
 
@@ -108,18 +136,22 @@ static int gk20a_dbg_gpu_do_dev_open(struct inode *inode,
  * since it might not have an associated channel. */
 static void gk20a_dbg_session_mutex_lock(struct dbg_session_gk20a *dbg_s)
 {
-        if (dbg_s->is_profiler)
+        struct channel_gk20a *ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+
+        if (dbg_s->is_profiler || !ch)
                 mutex_lock(&dbg_s->g->dbg_sessions_lock);
         else
-                mutex_lock(&dbg_s->ch->dbg_s_lock);
+                mutex_lock(&ch->dbg_s_lock);
 }
 
 static void gk20a_dbg_session_mutex_unlock(struct dbg_session_gk20a *dbg_s)
 {
-        if (dbg_s->is_profiler)
+        struct channel_gk20a *ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+
+        if (dbg_s->is_profiler || !ch)
                 mutex_unlock(&dbg_s->g->dbg_sessions_lock);
         else
-                mutex_unlock(&dbg_s->ch->dbg_s_lock);
+                mutex_unlock(&ch->dbg_s_lock);
 }
 
 static void gk20a_dbg_gpu_events_enable(struct dbg_session_gk20a *dbg_s)
@@ -163,10 +195,12 @@ static int gk20a_dbg_gpu_events_ctrl(struct dbg_session_gk20a *dbg_s,
                           struct nvgpu_dbg_gpu_events_ctrl_args *args)
 {
         int ret = 0;
+        struct channel_gk20a *ch;
 
         gk20a_dbg(gpu_dbg_fn | gpu_dbg_gpu_dbg, "dbg events ctrl cmd %d", args->cmd);
 
-        if (!dbg_s->ch) {
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+        if (!ch) {
                 gk20a_err(dev_from_gk20a(dbg_s->g),
                            "no channel bound to dbg session\n");
                 return -EINVAL;
@@ -235,6 +269,7 @@ int gk20a_prof_gpu_dev_open(struct inode *inode, struct file *filp)
 
 void gk20a_dbg_gpu_post_events(struct channel_gk20a *ch)
 {
+        struct dbg_session_data *session_data;
         struct dbg_session_gk20a *dbg_s;
 
         gk20a_dbg(gpu_dbg_fn | gpu_dbg_gpu_dbg, "");
@@ -242,7 +277,8 @@ void gk20a_dbg_gpu_post_events(struct channel_gk20a *ch)
         /* guard against the session list being modified */
         mutex_lock(&ch->dbg_s_lock);
 
-        list_for_each_entry(dbg_s, &ch->dbg_s_list, dbg_s_list_node) {
+        list_for_each_entry(session_data, &ch->dbg_s_list, dbg_s_entry) {
+                dbg_s = session_data->dbg_s;
                 if (dbg_s->dbg_events.events_enabled) {
                         gk20a_dbg(gpu_dbg_gpu_dbg, "posting event on session id %d",
                                         dbg_s->id);
@@ -260,6 +296,7 @@ void gk20a_dbg_gpu_post_events(struct channel_gk20a *ch)
 
 bool gk20a_dbg_gpu_broadcast_stop_trigger(struct channel_gk20a *ch)
 {
+        struct dbg_session_data *session_data;
         struct dbg_session_gk20a *dbg_s;
         bool broadcast = false;
 
@@ -268,7 +305,8 @@ bool gk20a_dbg_gpu_broadcast_stop_trigger(struct channel_gk20a *ch)
         /* guard against the session list being modified */
         mutex_lock(&ch->dbg_s_lock);
 
-        list_for_each_entry(dbg_s, &ch->dbg_s_list, dbg_s_list_node) {
+        list_for_each_entry(session_data, &ch->dbg_s_list, dbg_s_entry) {
+                dbg_s = session_data->dbg_s;
                 if (dbg_s->broadcast_stop_trigger) {
                         gk20a_dbg(gpu_dbg_gpu_dbg | gpu_dbg_fn | gpu_dbg_intr,
                                         "stop trigger broadcast enabled");
@@ -284,6 +322,7 @@ bool gk20a_dbg_gpu_broadcast_stop_trigger(struct channel_gk20a *ch)
 
 int gk20a_dbg_gpu_clear_broadcast_stop_trigger(struct channel_gk20a *ch)
 {
+        struct dbg_session_data *session_data;
         struct dbg_session_gk20a *dbg_s;
 
         gk20a_dbg(gpu_dbg_fn | gpu_dbg_gpu_dbg | gpu_dbg_intr, "");
@@ -291,7 +330,8 @@ int gk20a_dbg_gpu_clear_broadcast_stop_trigger(struct channel_gk20a *ch)
         /* guard against the session list being modified */
         mutex_lock(&ch->dbg_s_lock);
 
-        list_for_each_entry(dbg_s, &ch->dbg_s_list, dbg_s_list_node) {
+        list_for_each_entry(session_data, &ch->dbg_s_list, dbg_s_entry) {
+                dbg_s = session_data->dbg_s;
                 if (dbg_s->broadcast_stop_trigger) {
                         gk20a_dbg(gpu_dbg_gpu_dbg | gpu_dbg_fn | gpu_dbg_intr,
                                         "stop trigger broadcast disabled");
@@ -347,36 +387,87 @@ static int nvgpu_dbg_timeout_enable(struct dbg_session_gk20a *dbg_s,
         return err;
 }
 
-static int dbg_unbind_channel_gk20a(struct dbg_session_gk20a *dbg_s)
+int dbg_unbind_single_channel_gk20a(struct dbg_session_gk20a *dbg_s,
+                        struct dbg_session_channel_data *ch_data)
 {
-        struct channel_gk20a *ch_gk20a = dbg_s->ch;
         struct gk20a *g = dbg_s->g;
+        int chid;
+        struct channel_gk20a *ch;
+        struct dbg_session_data *session_data;
 
         gk20a_dbg(gpu_dbg_fn | gpu_dbg_gpu_dbg, "");
 
-        /* wasn't bound to start with ? */
-        if (!ch_gk20a) {
-                gk20a_dbg(gpu_dbg_gpu_dbg | gpu_dbg_fn, "not bound already?");
-                return -ENODEV;
-        }
+        chid = ch_data->chid;
+        ch = g->fifo.channel + chid;
 
-        mutex_lock(&g->dbg_sessions_lock);
-        mutex_lock(&ch_gk20a->dbg_s_lock);
+        list_del_init(&ch_data->ch_entry);
 
-        --g->dbg_sessions;
+        session_data = ch_data->session_data;
+        list_del_init(&session_data->dbg_s_entry);
+        kfree(session_data);
 
-        dbg_s->ch = NULL;
-        fput(dbg_s->ch_f);
-        dbg_s->ch_f = NULL;
+        fput(ch_data->ch_f);
+        kfree(ch_data);
 
-        list_del_init(&dbg_s->dbg_s_list_node);
+        return 0;
+}
+
+static int dbg_unbind_all_channels_gk20a(struct dbg_session_gk20a *dbg_s)
+{
+        struct dbg_session_channel_data *ch_data, *tmp;
+        struct gk20a *g = dbg_s->g;
 
-        mutex_unlock(&ch_gk20a->dbg_s_lock);
+        mutex_lock(&g->dbg_sessions_lock);
+        mutex_lock(&dbg_s->ch_list_lock);
+        list_for_each_entry_safe(ch_data, tmp, &dbg_s->ch_list, ch_entry)
+                dbg_unbind_single_channel_gk20a(dbg_s, ch_data);
+        mutex_unlock(&dbg_s->ch_list_lock);
         mutex_unlock(&g->dbg_sessions_lock);
 
         return 0;
 }
 
+static int dbg_unbind_channel_gk20a(struct dbg_session_gk20a *dbg_s,
+                          struct nvgpu_dbg_gpu_unbind_channel_args *args)
+{
+        struct dbg_session_channel_data *ch_data;
+        struct gk20a *g = dbg_s->g;
+        bool channel_found = false;
+        struct channel_gk20a *ch;
+        int err;
+
+        gk20a_dbg(gpu_dbg_fn|gpu_dbg_gpu_dbg, "%s fd=%d",
+                   dev_name(dbg_s->dev), args->channel_fd);
+
+        ch = gk20a_get_channel_from_file(args->channel_fd);
+        if (!ch) {
+                gk20a_dbg_fn("no channel found for fd");
+                return -EINVAL;
+        }
+
+        mutex_lock(&dbg_s->ch_list_lock);
+        list_for_each_entry(ch_data, &dbg_s->ch_list, ch_entry) {
+                if (ch->hw_chid == ch_data->chid) {
+                        channel_found = true;
+                        break;
+                }
+        }
+        mutex_unlock(&dbg_s->ch_list_lock);
+
+        if (!channel_found) {
+                gk20a_dbg_fn("channel not bounded, fd=%d\n", args->channel_fd);
+                return -EINVAL;
+        }
+
+        mutex_lock(&g->dbg_sessions_lock);
+        mutex_lock(&dbg_s->ch_list_lock);
+        err = dbg_unbind_single_channel_gk20a(dbg_s, ch_data);
+        mutex_unlock(&dbg_s->ch_list_lock);
+        mutex_unlock(&g->dbg_sessions_lock);
+
+        return err;
+}
+
 int gk20a_dbg_gpu_dev_release(struct inode *inode, struct file *filp)
 {
         struct dbg_session_gk20a *dbg_s = filp->private_data;
@@ -384,9 +475,8 @@ int gk20a_dbg_gpu_dev_release(struct inode *inode, struct file *filp)
 
         gk20a_dbg(gpu_dbg_gpu_dbg | gpu_dbg_fn, "%s", dev_name(dbg_s->dev));
 
-        /* unbind if it was bound */
-        if (dbg_s->ch)
-                dbg_unbind_channel_gk20a(dbg_s);
+        /* unbind channels */
+        dbg_unbind_all_channels_gk20a(dbg_s);
 
         /* Powergate/Timeout enable is called here as possibility of dbg_session
          * which called powergate/timeout disable ioctl, to be killed without
@@ -405,14 +495,28 @@ static int dbg_bind_channel_gk20a(struct dbg_session_gk20a *dbg_s,
                           struct nvgpu_dbg_gpu_bind_channel_args *args)
 {
         struct file *f;
-        struct gk20a *g;
+        struct gk20a *g = dbg_s->g;
         struct channel_gk20a *ch;
+        struct dbg_session_channel_data *ch_data, *tmp;
+        struct dbg_session_data *session_data;
 
         gk20a_dbg(gpu_dbg_fn|gpu_dbg_gpu_dbg, "%s fd=%d",
                    dev_name(dbg_s->dev), args->channel_fd);
 
-        if (args->channel_fd == ~0)
-                return dbg_unbind_channel_gk20a(dbg_s);
+        if (args->channel_fd == ~0) {
+                ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+                if (!ch)
+                        return -EINVAL;
+
+                mutex_lock(&dbg_s->ch_list_lock);
+                list_for_each_entry_safe(ch_data, tmp,
+                                         &dbg_s->ch_list, ch_entry) {
+                        if (ch_data->chid == ch->hw_chid)
+                                dbg_unbind_single_channel_gk20a(dbg_s, ch_data);
+                }
+                mutex_unlock(&dbg_s->ch_list_lock);
+                return 0;
+        }
 
         /* even though get_file_channel is doing this it releases it as well */
         /* by holding it here we'll keep it from disappearing while the
@@ -428,20 +532,40 @@ static int dbg_bind_channel_gk20a(struct dbg_session_gk20a *dbg_s,
                 return -EINVAL;
         }
 
-        g = dbg_s->g;
         gk20a_dbg_fn("%s hwchid=%d", dev_name(dbg_s->dev), ch->hw_chid);
 
         mutex_lock(&g->dbg_sessions_lock);
         mutex_lock(&ch->dbg_s_lock);
 
-        dbg_s->ch_f = f;
-        dbg_s->ch = ch;
-        list_add(&dbg_s->dbg_s_list_node, &dbg_s->ch->dbg_s_list);
+        ch_data = kzalloc(sizeof(*ch_data), GFP_KERNEL);
+        if (!ch_data) {
+                fput(f);
+                return -ENOMEM;
+        }
+        ch_data->ch_f = f;
+        ch_data->channel_fd = args->channel_fd;
+        ch_data->chid = ch->hw_chid;
+        INIT_LIST_HEAD(&ch_data->ch_entry);
+
+        session_data = kzalloc(sizeof(*session_data), GFP_KERNEL);
+        if (!session_data) {
+                kfree(ch_data);
+                fput(f);
+                return -ENOMEM;
+        }
+        session_data->dbg_s = dbg_s;
+        INIT_LIST_HEAD(&session_data->dbg_s_entry);
+        ch_data->session_data = session_data;
+
+        list_add(&session_data->dbg_s_entry, &ch->dbg_s_list);
 
-        g->dbg_sessions++;
+        mutex_lock(&dbg_s->ch_list_lock);
+        list_add_tail(&ch_data->ch_entry, &dbg_s->ch_list);
+        mutex_unlock(&dbg_s->ch_list_lock);
 
         mutex_unlock(&ch->dbg_s_lock);
         mutex_unlock(&g->dbg_sessions_lock);
+
         return 0;
 }
 
@@ -470,8 +594,12 @@ static int gk20a_perfbuf_unmap(struct dbg_session_gk20a *dbg_s,
 static int gk20a_dbg_pc_sampling(struct dbg_session_gk20a *dbg_s,
                           struct nvgpu_dbg_gpu_pc_sampling_args *args)
 {
-        struct channel_gk20a *ch = dbg_s->ch;
-        struct gk20a *g = ch->g;
+        struct channel_gk20a *ch;
+        struct gk20a *g = dbg_s->g;
+
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+        if (!ch)
+                return -EINVAL;
 
         gk20a_dbg_fn("");
 
@@ -571,9 +699,13 @@ static int nvgpu_dbg_gpu_ioctl_clear_single_sm_error_state(
         struct gk20a *g = get_gk20a(dbg_s->dev);
         struct gr_gk20a *gr = &g->gr;
         u32 sm_id;
-        struct channel_gk20a *ch = dbg_s->ch;
+        struct channel_gk20a *ch;
         int err = 0;
 
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+        if (!ch)
+                return -EINVAL;
+
         sm_id = args->sm_id;
 
         if (sm_id >= gr->no_of_sm)
@@ -598,10 +730,14 @@ static int nvgpu_dbg_gpu_ioctl_write_single_sm_error_state(
         struct gk20a *g = get_gk20a(dbg_s->dev);
         struct gr_gk20a *gr = &g->gr;
         u32 sm_id;
-        struct channel_gk20a *ch = dbg_s->ch;
+        struct channel_gk20a *ch;
         struct nvgpu_dbg_gpu_sm_error_state_record *sm_error_state;
         int err = 0;
 
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+        if (!ch)
+                return -EINVAL;
+
         sm_id = args->sm_id;
         if (sm_id >= gr->no_of_sm)
                 return -EINVAL;
@@ -756,6 +892,11 @@ long gk20a_dbg_gpu_dev_ioctl(struct file *filp, unsigned int cmd,
                   (struct nvgpu_dbg_gpu_write_single_sm_error_state_args *)buf);
                 break;
 
+        case NVGPU_DBG_GPU_IOCTL_UNBIND_CHANNEL:
+                err = dbg_unbind_channel_gk20a(dbg_s,
+                             (struct nvgpu_dbg_gpu_unbind_channel_args *)buf);
+                break;
+
         default:
                 gk20a_err(dev_from_gk20a(g),
                            "unrecognized dbg gpu ioctl cmd: 0x%x",
@@ -805,6 +946,7 @@ static int nvgpu_ioctl_channel_reg_ops(struct dbg_session_gk20a *dbg_s,
         struct device *dev = dbg_s->dev;
         struct gk20a *g = get_gk20a(dbg_s->dev);
         struct nvgpu_dbg_gpu_reg_op *ops;
+        struct channel_gk20a *ch;
         u64 ops_size = sizeof(ops[0]) * args->num_ops;
 
         gk20a_dbg_fn("%d ops, total size %llu", args->num_ops, ops_size);
@@ -814,7 +956,8 @@ static int nvgpu_ioctl_channel_reg_ops(struct dbg_session_gk20a *dbg_s,
                 return -EINVAL;
         }
 
-        if (!dbg_s->is_profiler && !dbg_s->ch) {
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+        if (!dbg_s->is_profiler && !ch) {
                 gk20a_err(dev, "bind a channel before regops for a debugging session");
                 return -EINVAL;
         }
@@ -1016,8 +1159,7 @@ static int nvgpu_dbg_gpu_ioctl_smpc_ctxsw_mode(struct dbg_session_gk20a *dbg_s,
         /* Take the global lock, since we'll be doing global regops */
         mutex_lock(&g->dbg_sessions_lock);
 
-        ch_gk20a = dbg_s->ch;
-
+        ch_gk20a = nvgpu_dbg_gpu_get_session_channel(dbg_s);
         if (!ch_gk20a) {
                 gk20a_err(dev_from_gk20a(g),
                           "no bound channel for smpc ctxsw mode update\n");
@@ -1052,8 +1194,7 @@ static int nvgpu_dbg_gpu_ioctl_hwpm_ctxsw_mode(struct dbg_session_gk20a *dbg_s,
         /* Take the global lock, since we'll be doing global regops */
         mutex_lock(&g->dbg_sessions_lock);
 
-        ch_gk20a = dbg_s->ch;
-
+        ch_gk20a = nvgpu_dbg_gpu_get_session_channel(dbg_s);
         if (!ch_gk20a) {
                 gk20a_err(dev_from_gk20a(g),
                           "no bound channel for pm ctxsw mode update\n");
@@ -1080,12 +1221,16 @@ static int nvgpu_dbg_gpu_ioctl_suspend_resume_sm(
                 struct nvgpu_dbg_gpu_suspend_resume_all_sms_args *args)
 {
         struct gk20a *g = get_gk20a(dbg_s->dev);
-        struct channel_gk20a *ch = dbg_s->ch;
+        struct channel_gk20a *ch;
         bool ch_is_curr_ctx;
         int err = 0, action = args->mode;
 
         gk20a_dbg(gpu_dbg_fn | gpu_dbg_gpu_dbg, "action: %d", args->mode);
 
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
+        if (!ch)
+                return -EINVAL;
+
         mutex_lock(&g->dbg_sessions_lock);
 
         /* Suspend GPU context switching */
diff --git a/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.h b/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.h
index 0ff6cfb3..d569a6cd 100644
--- a/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.h
+++ b/drivers/gpu/nvgpu/gk20a/dbg_gpu_gk20a.h
@@ -31,6 +31,9 @@ int gk20a_prof_gpu_dev_open(struct inode *inode, struct file *filp);
 /* used by the interrupt handler to post events */
 void gk20a_dbg_gpu_post_events(struct channel_gk20a *fault_ch);
 
+struct channel_gk20a *
+nvgpu_dbg_gpu_get_session_channel(struct dbg_session_gk20a *dbg_s);
+
 struct dbg_gpu_session_ops {
         int (*exec_reg_ops)(struct dbg_session_gk20a *dbg_s,
                             struct nvgpu_dbg_gpu_reg_op *ops,
@@ -68,22 +71,37 @@ struct dbg_session_gk20a {
         struct device             *dev;
         struct gk20a              *g;
 
-        /* bound channel, if any */
-        struct file          *ch_f;
-        struct channel_gk20a *ch;
+        /* list of bound channels, if any */
+        struct list_head ch_list;
+        struct mutex ch_list_lock;
 
         /* session operations */
         struct dbg_gpu_session_ops *ops;
 
         /* event support */
         struct dbg_gpu_session_events dbg_events;
-        struct list_head dbg_s_list_node;
 
         bool broadcast_stop_trigger;
 };
 
+struct dbg_session_data {
+        struct dbg_session_gk20a *dbg_s;
+        struct list_head dbg_s_entry;
+};
+
+struct dbg_session_channel_data {
+        struct file          *ch_f;
+        int channel_fd;
+        int chid;
+        struct list_head ch_entry;
+        struct dbg_session_data *session_data;
+};
+
 extern struct dbg_gpu_session_ops dbg_gpu_session_ops_gk20a;
 
+int dbg_unbind_single_channel_gk20a(struct dbg_session_gk20a *dbg_s,
+                        struct dbg_session_channel_data *ch_data);
+
 bool gk20a_dbg_gpu_broadcast_stop_trigger(struct channel_gk20a *ch);
 int gk20a_dbg_gpu_clear_broadcast_stop_trigger(struct channel_gk20a *ch);
 
diff --git a/drivers/gpu/nvgpu/gk20a/gk20a.h b/drivers/gpu/nvgpu/gk20a/gk20a.h
index d1ce6afb..b03e779b 100644
--- a/drivers/gpu/nvgpu/gk20a/gk20a.h
+++ b/drivers/gpu/nvgpu/gk20a/gk20a.h
@@ -647,7 +647,6 @@ struct gk20a {
         /* held while manipulating # of debug/profiler sessions present */
         /* also prevents debug sessions from attaching until released */
         struct mutex dbg_sessions_lock;
-        int dbg_sessions; /* number attached */
         int dbg_powergating_disabled_refcount; /*refcount for pg disable */
         int dbg_timeout_disabled_refcount; /*refcount for timeout disable */
 
diff --git a/drivers/gpu/nvgpu/gk20a/regops_gk20a.c b/drivers/gpu/nvgpu/gk20a/regops_gk20a.c
index fda480cf..6e21e857 100644
--- a/drivers/gpu/nvgpu/gk20a/regops_gk20a.c
+++ b/drivers/gpu/nvgpu/gk20a/regops_gk20a.c
@@ -390,7 +390,7 @@ int exec_regops_gk20a(struct dbg_session_gk20a *dbg_s,
 
         gk20a_dbg(gpu_dbg_fn | gpu_dbg_gpu_dbg, "");
 
-        ch = dbg_s->ch;
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
 
         /* For vgpu, the regops routines need to be handled in the
          * context of the server and support for that does not exist.
@@ -559,6 +559,9 @@ static bool check_whitelists(struct dbg_session_gk20a *dbg_s,
 {
         struct gk20a *g = dbg_s->g;
         bool valid = false;
+        struct channel_gk20a *ch;
+
+        ch = nvgpu_dbg_gpu_get_session_channel(dbg_s);
 
         if (op->type == REGOP(TYPE_GLOBAL)) {
                 /* search global list */
@@ -570,7 +573,7 @@ static bool check_whitelists(struct dbg_session_gk20a *dbg_s,
                         regop_bsearch_range_cmp);
 
                 /* if debug session and channel is bound search context list */
-                if ((!valid) && (!dbg_s->is_profiler && dbg_s->ch)) {
+                if ((!valid) && (!dbg_s->is_profiler && ch)) {
                         /* binary search context list */
                         valid = g->ops.regops.get_context_whitelist_ranges &&
                                 !!bsearch(&offset,
@@ -581,7 +584,7 @@ static bool check_whitelists(struct dbg_session_gk20a *dbg_s,
                 }
 
                 /* if debug session and channel is bound search runcontrol list */
-                if ((!valid) && (!dbg_s->is_profiler && dbg_s->ch)) {
+                if ((!valid) && (!dbg_s->is_profiler && ch)) {
                         valid = g->ops.regops.get_runcontrol_whitelist &&
                                 linear_search(offset,
                                 g->ops.regops.get_runcontrol_whitelist(),
@@ -589,7 +592,7 @@ static bool check_whitelists(struct dbg_session_gk20a *dbg_s,
                 }
         } else if (op->type == REGOP(TYPE_GR_CTX)) {
                 /* it's a context-relative op */
-                if (!dbg_s->ch) {
+                if (!ch) {
                         gk20a_err(dbg_s->dev, "can't perform ctx regop unless bound");
                         op->status = REGOP(STATUS_UNSUPPORTED_OP);
                         return valid;
@@ -604,7 +607,7 @@ static bool check_whitelists(struct dbg_session_gk20a *dbg_s,
                         regop_bsearch_range_cmp);
 
                 /* if debug session and channel is bound search runcontrol list */
-                if ((!valid) && (!dbg_s->is_profiler && dbg_s->ch)) {
+                if ((!valid) && (!dbg_s->is_profiler && ch)) {
                         valid = g->ops.regops.get_runcontrol_whitelist &&
                                 linear_search(offset,
                                 g->ops.regops.get_runcontrol_whitelist(),