[RFC] staging: vchiq_arm: move state dump to debugfs

Besides the IOCTL interface the VCHIQ character device also provides
a state dump of the whole VCHIQ driver via read. Moving the state dump
function to debugfs has a lot advantages:

- following changes on state dump doesn't break userspace ABI
- debug doesn't depend on VCHIQ_CDEV
- dump code simplifies a lot and reduce the chance of buffer overflows

Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
---

Hello,

since recent discussion raised the question about the future of debugfs
for vchiq [1], i want to submit this cleanup patch as part of the
discussion. The patch itself based on the latest series [2] of
Umang Jain to convert VCHIQ into a bus. I'm aware of the checkpatch
warnings which will be fixed in the next version, but not revelant
to the discussion.

Best regards

[1] - https://lore.kernel.org/lkml/7ea529c2-3da6-47df-9b09-28d4ab36c4ef@kadam.mountain/T/
[2] - https://lore.kernel.org/linux-arm-kernel/dc6d4108-7bb0-ba81-2f6b-0409b848ab0d@ideasonboard.com/T/#t

 .../interface/vchiq_arm/vchiq_arm.c           |  94 ++-----
 .../interface/vchiq_arm/vchiq_arm.h           |   7 -
 .../interface/vchiq_arm/vchiq_core.c          | 236 ++++++------------
 .../interface/vchiq_arm/vchiq_core.h          |  17 +-
 .../interface/vchiq_arm/vchiq_debugfs.c       |  10 +
 .../interface/vchiq_arm/vchiq_dev.c           |  21 --
 6 files changed, 116 insertions(+), 269 deletions(-)

--
2.34.1

Hi Stefan,

On Sun, Sep 24, 2023 at 01:53:25AM +0200, Stefan Wahren wrote:
> Besides the IOCTL interface the VCHIQ character device also provides
> a state dump of the whole VCHIQ driver via read. Moving the state dump
> function to debugfs has a lot advantages:
> 
> - following changes on state dump doesn't break userspace ABI
> - debug doesn't depend on VCHIQ_CDEV
> - dump code simplifies a lot and reduce the chance of buffer overflows
> 
> Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
> ---
> 
> Hello,
> 
> since recent discussion raised the question about the future of debugfs
> for vchiq [1], i want to submit this cleanup patch as part of the
> discussion. The patch itself based on the latest series [2] of
> Umang Jain to convert VCHIQ into a bus. I'm aware of the checkpatch
> warnings which will be fixed in the next version, but not revelant
> to the discussion.

I personally like debugfs for this. Assuming we can switch without
userspace screaming at us (and I suppose that being in staging helps),
this patch looks good to me.

> [1] - https://lore.kernel.org/lkml/7ea529c2-3da6-47df-9b09-28d4ab36c4ef@kadam.mountain/T/
> [2] - https://lore.kernel.org/linux-arm-kernel/dc6d4108-7bb0-ba81-2f6b-0409b848ab0d@ideasonboard.com/T/#t
> 
>  .../interface/vchiq_arm/vchiq_arm.c           |  94 ++-----
>  .../interface/vchiq_arm/vchiq_arm.h           |   7 -
>  .../interface/vchiq_arm/vchiq_core.c          | 236 ++++++------------
>  .../interface/vchiq_arm/vchiq_core.h          |  17 +-
>  .../interface/vchiq_arm/vchiq_debugfs.c       |  10 +
>  .../interface/vchiq_arm/vchiq_dev.c           |  21 --
>  6 files changed, 116 insertions(+), 269 deletions(-)

I certainly like this too :-)

> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> index 5eccf5b277e5..150b85ce29da 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> @@ -662,13 +662,9 @@ vchiq_complete_bulk(struct vchiq_instance *instance, struct vchiq_bulk *bulk)
>  			      bulk->actual);
>  }
> 
> -int vchiq_dump_platform_state(void *dump_context)
> +void vchiq_dump_platform_state(struct seq_file *f)
>  {
> -	char buf[80];
> -	int len;
> -
> -	len = snprintf(buf, sizeof(buf), "  Platform: 2835 (VC master)");
> -	return vchiq_dump(dump_context, buf, len + 1);
> +	seq_puts(f, "  Platform: 2835 (VC master)\n");
>  }
> 
>  #define VCHIQ_INIT_RETRIES 10
> @@ -1177,56 +1173,13 @@ service_callback(struct vchiq_instance *instance, enum vchiq_reason reason,
>  		bulk_userdata);
>  }
> 
> -int vchiq_dump(void *dump_context, const char *str, int len)
> -{
> -	struct dump_context *context = (struct dump_context *)dump_context;
> -	int copy_bytes;
> -
> -	if (context->actual >= context->space)
> -		return 0;
> -
> -	if (context->offset > 0) {
> -		int skip_bytes = min_t(int, len, context->offset);
> -
> -		str += skip_bytes;
> -		len -= skip_bytes;
> -		context->offset -= skip_bytes;
> -		if (context->offset > 0)
> -			return 0;
> -	}
> -	copy_bytes = min_t(int, len, context->space - context->actual);
> -	if (copy_bytes == 0)
> -		return 0;
> -	if (copy_to_user(context->buf + context->actual, str,
> -			 copy_bytes))
> -		return -EFAULT;
> -	context->actual += copy_bytes;
> -	len -= copy_bytes;
> -
> -	/*
> -	 * If the terminating NUL is included in the length, then it
> -	 * marks the end of a line and should be replaced with a
> -	 * carriage return.
> -	 */
> -	if ((len == 0) && (str[copy_bytes - 1] == '\0')) {
> -		char cr = '\n';
> -
> -		if (copy_to_user(context->buf + context->actual - 1,
> -				 &cr, 1))
> -			return -EFAULT;
> -	}
> -	return 0;
> -}
> -
> -int vchiq_dump_platform_instances(void *dump_context)
> +void vchiq_dump_platform_instances(struct seq_file *f)
>  {
>  	struct vchiq_state *state = vchiq_get_state();
> -	char buf[80];
> -	int len;
>  	int i;
> 
>  	if (!state)
> -		return -ENOTCONN;
> +		return;
> 
>  	/*
>  	 * There is no list of instances, so instead scan all services,
> @@ -1251,7 +1204,6 @@ int vchiq_dump_platform_instances(void *dump_context)
>  	for (i = 0; i < state->unused_service; i++) {
>  		struct vchiq_service *service;
>  		struct vchiq_instance *instance;
> -		int err;
> 
>  		rcu_read_lock();
>  		service = rcu_dereference(state->services[i]);
> @@ -1267,43 +1219,35 @@ int vchiq_dump_platform_instances(void *dump_context)
>  		}
>  		rcu_read_unlock();
> 
> -		len = snprintf(buf, sizeof(buf),
> -			       "Instance %pK: pid %d,%s completions %d/%d",
> -			       instance, instance->pid,
> -			       instance->connected ? " connected, " :
> -			       "",
> -			       instance->completion_insert -
> -			       instance->completion_remove,
> -			       MAX_COMPLETIONS);
> -		err = vchiq_dump(dump_context, buf, len + 1);
> -		if (err)
> -			return err;
> +		seq_printf(f, "Instance %pK: pid %d,%s completions %d/%d\n",
> +			   instance, instance->pid,
> +			   instance->connected ? " connected, " :
> +			   "",
> +			   instance->completion_insert -
> +			   instance->completion_remove,
> +			   MAX_COMPLETIONS);
>  		instance->mark = 1;
>  	}
> -	return 0;
>  }
> 
> -int vchiq_dump_platform_service_state(void *dump_context,
> -				      struct vchiq_service *service)
> +void vchiq_dump_platform_service_state(struct seq_file *f,
> +				       struct vchiq_service *service)
>  {
>  	struct user_service *user_service =
>  			(struct user_service *)service->base.userdata;
> -	char buf[80];
> -	int len;
> 
> -	len = scnprintf(buf, sizeof(buf), "  instance %pK", service->instance);
> +	seq_printf(f, "  instance %pK", service->instance);
> 
>  	if ((service->base.callback == service_callback) && user_service->is_vchi) {
> -		len += scnprintf(buf + len, sizeof(buf) - len, ", %d/%d messages",
> -				 user_service->msg_insert - user_service->msg_remove,
> -				 MSG_QUEUE_SIZE);
> +		seq_printf(f, ", %d/%d messages",
> +			   user_service->msg_insert - user_service->msg_remove,
> +			   MSG_QUEUE_SIZE);
> 
>  		if (user_service->dequeue_pending)
> -			len += scnprintf(buf + len, sizeof(buf) - len,
> -				" (dequeue pending)");
> +			seq_puts(f, " (dequeue pending)");
>  	}
> 
> -	return vchiq_dump(dump_context, buf, len + 1);
> +	seq_puts(f, "\n");
>  }
> 
>  struct vchiq_state *
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
> index 2fb31f9b527f..372f4d06ffbb 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
> @@ -69,13 +69,6 @@ struct vchiq_instance {
>  	struct vchiq_debugfs_node debugfs_node;
>  };
> 
> -struct dump_context {
> -	char __user *buf;
> -	size_t actual;
> -	size_t space;
> -	loff_t offset;
> -};
> -
>  extern int vchiq_arm_log_level;
>  extern int vchiq_susp_log_level;
> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c
> index 596894338cb4..fa234d460401 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c
> @@ -3394,8 +3394,8 @@ vchiq_set_service_option(struct vchiq_instance *instance, unsigned int handle,
>  	return ret;
>  }
> 
> -static int
> -vchiq_dump_shared_state(void *dump_context, struct vchiq_state *state,
> +static void
> +vchiq_dump_shared_state(struct seq_file *f, struct vchiq_state *state,
>  			struct vchiq_shared_state *shared, const char *label)
>  {
>  	static const char *const debug_names[] = {
> @@ -3412,139 +3412,83 @@ vchiq_dump_shared_state(void *dump_context, struct vchiq_state *state,
>  		"COMPLETION_QUEUE_FULL_COUNT"
>  	};
>  	int i;
> -	char buf[80];
> -	int len;
> -	int err;
> -
> -	len = scnprintf(buf, sizeof(buf), "  %s: slots %d-%d tx_pos=%x recycle=%x",
> -			label, shared->slot_first, shared->slot_last,
> -			shared->tx_pos, shared->slot_queue_recycle);
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> -
> -	len = scnprintf(buf, sizeof(buf), "    Slots claimed:");
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> +
> +	seq_printf(f, "  %s: slots %d-%d tx_pos=%x recycle=%x\n",
> +		   label, shared->slot_first, shared->slot_last,
> +		   shared->tx_pos, shared->slot_queue_recycle);
> +
> +	seq_puts(f, "    Slots claimed:\n");
> 
>  	for (i = shared->slot_first; i <= shared->slot_last; i++) {
>  		struct vchiq_slot_info slot_info =
>  						*SLOT_INFO_FROM_INDEX(state, i);
>  		if (slot_info.use_count != slot_info.release_count) {
> -			len = scnprintf(buf, sizeof(buf), "      %d: %d/%d", i, slot_info.use_count,
> -					slot_info.release_count);
> -			err = vchiq_dump(dump_context, buf, len + 1);
> -			if (err)
> -				return err;
> +			seq_printf(f, "      %d: %d/%d\n", i, slot_info.use_count,
> +				   slot_info.release_count);
>  		}
>  	}
> 
>  	for (i = 1; i < shared->debug[DEBUG_ENTRIES]; i++) {
> -		len = scnprintf(buf, sizeof(buf), "    DEBUG: %s = %d(%x)",
> -				debug_names[i], shared->debug[i], shared->debug[i]);
> -		err = vchiq_dump(dump_context, buf, len + 1);
> -		if (err)
> -			return err;
> +		seq_printf(f, "    DEBUG: %s = %d(%x)\n",
> +			   debug_names[i], shared->debug[i], shared->debug[i]);
>  	}
> -	return 0;
>  }
> 
> -int vchiq_dump_state(void *dump_context, struct vchiq_state *state)
> +void vchiq_dump_state(struct seq_file *f, struct vchiq_state *state)
>  {
> -	char buf[80];
> -	int len;
>  	int i;
> -	int err;
> -
> -	len = scnprintf(buf, sizeof(buf), "State %d: %s", state->id,
> -			conn_state_names[state->conn_state]);
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> -
> -	len = scnprintf(buf, sizeof(buf), "  tx_pos=%x(@%pK), rx_pos=%x(@%pK)",
> -			state->local->tx_pos,
> -			state->tx_data + (state->local_tx_pos & VCHIQ_SLOT_MASK),
> -			state->rx_pos,
> -			state->rx_data + (state->rx_pos & VCHIQ_SLOT_MASK));
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> -
> -	len = scnprintf(buf, sizeof(buf), "  Version: %d (min %d)",
> -			VCHIQ_VERSION, VCHIQ_VERSION_MIN);
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> +
> +	seq_printf(f, "State %d: %s\n", state->id,
> +		   conn_state_names[state->conn_state]);
> +
> +	seq_printf(f, "  tx_pos=%x(@%pK), rx_pos=%x(@%pK)\n",
> +		   state->local->tx_pos,
> +		   state->tx_data + (state->local_tx_pos & VCHIQ_SLOT_MASK),
> +		   state->rx_pos,
> +		   state->rx_data + (state->rx_pos & VCHIQ_SLOT_MASK));
> +
> +	seq_printf(f, "  Version: %d (min %d)\n", VCHIQ_VERSION,
> +		   VCHIQ_VERSION_MIN);
> 
>  	if (VCHIQ_ENABLE_STATS) {
> -		len = scnprintf(buf, sizeof(buf),
> -				"  Stats: ctrl_tx_count=%d, ctrl_rx_count=%d, error_count=%d",
> -				state->stats.ctrl_tx_count, state->stats.ctrl_rx_count,
> -				state->stats.error_count);
> -		err = vchiq_dump(dump_context, buf, len + 1);
> -		if (err)
> -			return err;
> -	}
> -
> -	len = scnprintf(buf, sizeof(buf),
> -			"  Slots: %d available (%d data), %d recyclable, %d stalls (%d data)",
> -			((state->slot_queue_available * VCHIQ_SLOT_SIZE) -
> -			state->local_tx_pos) / VCHIQ_SLOT_SIZE,
> -			state->data_quota - state->data_use_count,
> -			state->local->slot_queue_recycle - state->slot_queue_available,
> -			state->stats.slot_stalls, state->stats.data_stalls);
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> -
> -	err = vchiq_dump_platform_state(dump_context);
> -	if (err)
> -		return err;
> -
> -	err = vchiq_dump_shared_state(dump_context,
> -				      state,
> -				      state->local,
> -				      "Local");
> -	if (err)
> -		return err;
> -	err = vchiq_dump_shared_state(dump_context,
> -				      state,
> -				      state->remote,
> -				      "Remote");
> -	if (err)
> -		return err;
> -
> -	err = vchiq_dump_platform_instances(dump_context);
> -	if (err)
> -		return err;
> +		seq_printf(f, "  Stats: ctrl_tx_count=%d, ctrl_rx_count=%d, error_count=%d\n",
> +			   state->stats.ctrl_tx_count, state->stats.ctrl_rx_count,
> +			   state->stats.error_count);
> +	}
> +
> +	seq_printf(f, "  Slots: %d available (%d data), %d recyclable, %d stalls (%d data)\n",
> +		   ((state->slot_queue_available * VCHIQ_SLOT_SIZE) -
> +		   state->local_tx_pos) / VCHIQ_SLOT_SIZE,
> +		   state->data_quota - state->data_use_count,
> +		   state->local->slot_queue_recycle - state->slot_queue_available,
> +		   state->stats.slot_stalls, state->stats.data_stalls);
> +
> +	vchiq_dump_platform_state(f);
> +
> +	vchiq_dump_shared_state(f, state, state->local, "Local");
> +
> +	vchiq_dump_shared_state(f, state, state->remote, "Remote");
> +
> +	vchiq_dump_platform_instances(f);
> 
>  	for (i = 0; i < state->unused_service; i++) {
>  		struct vchiq_service *service = find_service_by_port(state, i);
> 
>  		if (service) {
> -			err = vchiq_dump_service_state(dump_context, service);
> +			vchiq_dump_service_state(f, service);
>  			vchiq_service_put(service);
> -			if (err)
> -				return err;
>  		}
>  	}
> -	return 0;
>  }
> 
> -int vchiq_dump_service_state(void *dump_context, struct vchiq_service *service)
> +void vchiq_dump_service_state(struct seq_file *f, struct vchiq_service *service)
>  {
> -	char buf[80];
> -	int len;
> -	int err;
>  	unsigned int ref_count;
> 
>  	/*Don't include the lock just taken*/
>  	ref_count = kref_read(&service->ref_count) - 1;
> -	len = scnprintf(buf, sizeof(buf), "Service %u: %s (ref %u)",
> -			service->localport, srvstate_names[service->srvstate],
> -			ref_count);
> +	seq_printf(f, "Service %u: %s (ref %u)", service->localport,
> +		   srvstate_names[service->srvstate], ref_count);
> 
>  	if (service->srvstate != VCHIQ_SRVSTATE_FREE) {
>  		char remoteport[30];
> @@ -3564,15 +3508,10 @@ int vchiq_dump_service_state(void *dump_context, struct vchiq_service *service)
>  			strscpy(remoteport, "n/a", sizeof(remoteport));
>  		}
> 
> -		len += scnprintf(buf + len, sizeof(buf) - len,
> -				 " '%c%c%c%c' remote %s (msg use %d/%d, slot use %d/%d)",
> -				 VCHIQ_FOURCC_AS_4CHARS(fourcc), remoteport,
> -				 quota->message_use_count, quota->message_quota,
> -				 quota->slot_use_count, quota->slot_quota);
> -
> -		err = vchiq_dump(dump_context, buf, len + 1);
> -		if (err)
> -			return err;
> +		seq_printf(f, " '%c%c%c%c' remote %s (msg use %d/%d, slot use %d/%d)\n",
> +			   VCHIQ_FOURCC_AS_4CHARS(fourcc), remoteport,
> +			   quota->message_use_count, quota->message_quota,
> +			   quota->slot_use_count, quota->slot_quota);
> 
>  		tx_pending = service->bulk_tx.local_insert -
>  			service->bulk_tx.remote_insert;
> @@ -3580,52 +3519,35 @@ int vchiq_dump_service_state(void *dump_context, struct vchiq_service *service)
>  		rx_pending = service->bulk_rx.local_insert -
>  			service->bulk_rx.remote_insert;
> 
> -		len = scnprintf(buf, sizeof(buf),
> -				"  Bulk: tx_pending=%d (size %d), rx_pending=%d (size %d)",
> -				tx_pending,
> -				tx_pending ?
> -				service->bulk_tx.bulks[BULK_INDEX(service->bulk_tx.remove)].size :
> -				0, rx_pending, rx_pending ?
> -				service->bulk_rx.bulks[BULK_INDEX(service->bulk_rx.remove)].size :
> -				0);
> +		seq_printf(f, "  Bulk: tx_pending=%d (size %d), rx_pending=%d (size %d)\n",
> +			   tx_pending,
> +			   tx_pending ? service->bulk_tx.bulks[BULK_INDEX(service->bulk_tx.remove)].size : 0,
> +			   rx_pending,
> +			   rx_pending ? service->bulk_rx.bulks[BULK_INDEX(service->bulk_rx.remove)].size : 0);
> 
>  		if (VCHIQ_ENABLE_STATS) {
> -			err = vchiq_dump(dump_context, buf, len + 1);
> -			if (err)
> -				return err;
> -
> -			len = scnprintf(buf, sizeof(buf),
> -					"  Ctrl: tx_count=%d, tx_bytes=%llu, rx_count=%d, rx_bytes=%llu",
> -					service->stats.ctrl_tx_count, service->stats.ctrl_tx_bytes,
> -					service->stats.ctrl_rx_count, service->stats.ctrl_rx_bytes);
> -			err = vchiq_dump(dump_context, buf, len + 1);
> -			if (err)
> -				return err;
> -
> -			len = scnprintf(buf, sizeof(buf),
> -					"  Bulk: tx_count=%d, tx_bytes=%llu, rx_count=%d, rx_bytes=%llu",
> -					service->stats.bulk_tx_count, service->stats.bulk_tx_bytes,
> -					service->stats.bulk_rx_count, service->stats.bulk_rx_bytes);
> -			err = vchiq_dump(dump_context, buf, len + 1);
> -			if (err)
> -				return err;
> -
> -			len = scnprintf(buf, sizeof(buf),
> -					"  %d quota stalls, %d slot stalls, %d bulk stalls, %d aborted, %d errors",
> -					service->stats.quota_stalls, service->stats.slot_stalls,
> -					service->stats.bulk_stalls,
> -					service->stats.bulk_aborted_count,
> -					service->stats.error_count);
> -		}
> -	}
> -
> -	err = vchiq_dump(dump_context, buf, len + 1);
> -	if (err)
> -		return err;
> -
> -	if (service->srvstate != VCHIQ_SRVSTATE_FREE)
> -		err = vchiq_dump_platform_service_state(dump_context, service);
> -	return err;
> +			seq_printf(f, "  Ctrl: tx_count=%d, tx_bytes=%llu, rx_count=%d, rx_bytes=%llu\n",
> +				   service->stats.ctrl_tx_count,
> +				   service->stats.ctrl_tx_bytes,
> +				   service->stats.ctrl_rx_count,
> +				   service->stats.ctrl_rx_bytes);
> +
> +			seq_printf(f, "  Bulk: tx_count=%d, tx_bytes=%llu, rx_count=%d, rx_bytes=%llu\n",
> +				   service->stats.bulk_tx_count,
> +				   service->stats.bulk_tx_bytes,
> +				   service->stats.bulk_rx_count,
> +				   service->stats.bulk_rx_bytes);
> +
> +			seq_printf(f, "  %d quota stalls, %d slot stalls, %d bulk stalls, %d aborted, %d errors\n",
> +				   service->stats.quota_stalls,
> +				   service->stats.slot_stalls,
> +				   service->stats.bulk_stalls,
> +				   service->stats.bulk_aborted_count,
> +				   service->stats.error_count);
> +		}
> +	}
> +
> +	vchiq_dump_platform_service_state(f, service);
>  }
> 
>  void
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h
> index ec1a3caefaea..8568e37f89e0 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.h
> @@ -6,6 +6,7 @@
> 
>  #include <linux/mutex.h>
>  #include <linux/completion.h>
> +#include <linux/debugfs.h>
>  #include <linux/kthread.h>
>  #include <linux/kref.h>
>  #include <linux/rcupdate.h>
> @@ -508,11 +509,11 @@ vchiq_bulk_transfer(struct vchiq_instance *instance, unsigned int handle, void *
>  		    void __user *uoffset, int size, void *userdata, enum vchiq_bulk_mode mode,
>  		    enum vchiq_bulk_dir dir);
> 
> -extern int
> -vchiq_dump_state(void *dump_context, struct vchiq_state *state);
> +extern void
> +vchiq_dump_state(struct seq_file *f, struct vchiq_state *state);
> 
> -extern int
> -vchiq_dump_service_state(void *dump_context, struct vchiq_service *service);
> +extern void
> +vchiq_dump_service_state(struct seq_file *f, struct vchiq_service *service);

This function is defined and called from vchiq_core.c only, you can drop
it from here and make it static.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> 
>  extern void
>  vchiq_loud_error_header(void);
> @@ -568,13 +569,11 @@ void vchiq_complete_bulk(struct vchiq_instance *instance, struct vchiq_bulk *bul
> 
>  void remote_event_signal(struct remote_event *event);
> 
> -int vchiq_dump(void *dump_context, const char *str, int len);
> -
> -int vchiq_dump_platform_state(void *dump_context);
> +void vchiq_dump_platform_state(struct seq_file *f);
> 
> -int vchiq_dump_platform_instances(void *dump_context);
> +void vchiq_dump_platform_instances(struct seq_file *f);
> 
> -int vchiq_dump_platform_service_state(void *dump_context, struct vchiq_service *service);
> +void vchiq_dump_platform_service_state(struct seq_file *f, struct vchiq_service *service);
> 
>  int vchiq_use_service_internal(struct vchiq_service *service);
> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_debugfs.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_debugfs.c
> index dc667afd1f8c..0333da728011 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_debugfs.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_debugfs.c
> @@ -36,6 +36,13 @@ static struct vchiq_debugfs_log_entry vchiq_debugfs_log_entries[] = {
>  	{ "arm",  &vchiq_arm_log_level },
>  };
> 
> +static int vchiq_dump_show(struct seq_file *f, void *offset)
> +{
> +	vchiq_dump_state(f, &g_state);
> +	return 0;
> +}
> +DEFINE_SHOW_ATTRIBUTE(vchiq_dump);
> +
>  static int debugfs_log_show(struct seq_file *f, void *offset)
>  {
>  	int *levp = f->private;
> @@ -211,6 +218,9 @@ void vchiq_debugfs_init(void)
>  	vchiq_dbg_dir = debugfs_create_dir("vchiq", NULL);
>  	vchiq_dbg_clients = debugfs_create_dir("clients", vchiq_dbg_dir);
> 
> +	debugfs_create_file("state", S_IFREG | 0444, vchiq_dbg_dir, NULL,
> +			    &vchiq_dump_fops);
> +
>  	/* create an entry under <debugfs>/vchiq/log for each log category */
>  	dir = debugfs_create_dir("log", vchiq_dbg_dir);
> 
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_dev.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_dev.c
> index 841e1a535642..ec043e8e60c7 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_dev.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_dev.c
> @@ -1306,26 +1306,6 @@ static int vchiq_release(struct inode *inode, struct file *file)
>  	return ret;
>  }
> 
> -static ssize_t
> -vchiq_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> -{
> -	struct dump_context context;
> -	int err;
> -
> -	context.buf = buf;
> -	context.actual = 0;
> -	context.space = count;
> -	context.offset = *ppos;
> -
> -	err = vchiq_dump_state(&context, &g_state);
> -	if (err)
> -		return err;
> -
> -	*ppos += context.actual;
> -
> -	return context.actual;
> -}
> -
>  static const struct file_operations
>  vchiq_fops = {
>  	.owner = THIS_MODULE,
> @@ -1335,7 +1315,6 @@ vchiq_fops = {
>  #endif
>  	.open = vchiq_open,
>  	.release = vchiq_release,
> -	.read = vchiq_read
>  };
> 
>  static struct miscdevice vchiq_miscdev = {