[PATCH v12 4/7] iio: buffer-dma: Enable support for DMABUFs

Paul Cercueil
2024-06-20T12:28:23Z

Implement iio_dma_buffer_attach_dmabuf(), iio_dma_buffer_detach_dmabuf()
and iio_dma_buffer_transfer_dmabuf(), which can then be used by the IIO
DMA buffer implementations.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Co-developed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v3: Update code to provide the functions that will be used as callbacks
for the new IOCTLs.

v6: - Update iio_dma_buffer_enqueue_dmabuf() to take a dma_fence pointer
- Pass that dma_fence pointer along to
iio_buffer_signal_dmabuf_done()
- Add iio_dma_buffer_lock_queue() / iio_dma_buffer_unlock_queue()
- Do not lock the queue in iio_dma_buffer_enqueue_dmabuf().
The caller will ensure that it has been locked already.
- Replace "int += bool;" by "if (bool) int++;"
- Use dma_fence_begin/end_signalling in the dma_fence critical
sections
- Use one "num_dmabufs" fields instead of one "num_blocks" and one
"num_fileio_blocks". Make it an atomic_t, which makes it possible
to decrement it atomically in iio_buffer_block_release() without
having to lock the queue mutex; and in turn, it means that we
don't need to use iio_buffer_block_put_atomic() everywhere to
avoid locking the queue mutex twice.
- Use cleanup.h guard(mutex) when possible
- Explicitely list all states in the switch in
iio_dma_can_enqueue_block()
- Rename iio_dma_buffer_fileio_mode() to
iio_dma_buffer_can_use_fileio(), and add a comment explaining why
it cannot race vs. DMABUF.

v11:
- Remove useless field "attach" in struct iio_dma_buffer_block
- Document "sg_table" and "fence" fields in struct iio_block_state
---
drivers/iio/buffer/industrialio-buffer-dma.c | 178 +++++++++++++++++--
include/linux/iio/buffer-dma.h | 31 ++++
2 files changed, 198 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index 13b1a858969e..647f417a045e 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -4,6 +4,8 @@
* Author: Lars-Peter Clausen <lars@metafoo.de>
*/

+#include <linux/atomic.h>
+#include <linux/cleanup.h>
#include <linux/slab.h>
#include <linux/kernel.h>
#include <linux/module.h>
@@ -14,6 +16,8 @@
#include <linux/poll.h>
#include <linux/iio/buffer_impl.h>
#include <linux/iio/buffer-dma.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-fence.h>
#include <linux/dma-mapping.h>
#include <linux/sizes.h>

@@ -94,13 +98,18 @@ static void iio_buffer_block_release(struct kref *kref)
{
struct iio_dma_buffer_block *block = container_of(kref,
struct iio_dma_buffer_block, kref);
+ struct iio_dma_buffer_queue *queue = block->queue;

- WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
+ WARN_ON(block->fileio && block->state != IIO_BLOCK_STATE_DEAD);

- dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
- block->vaddr, block->phys_addr);
+ if (block->fileio) {
+ dma_free_coherent(queue->dev, PAGE_ALIGN(block->size),
+ block->vaddr, block->phys_addr);
+ } else {
+ atomic_dec(&queue->num_dmabufs);
+ }

- iio_buffer_put(&block->queue->buffer);
+ iio_buffer_put(&queue->buffer);
kfree(block);
}

@@ -163,7 +172,7 @@ static struct iio_dma_buffer_queue *iio_buffer_to_queue(struct iio_buffer *buf)
}

static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
- struct iio_dma_buffer_queue *queue, size_t size)
+ struct iio_dma_buffer_queue *queue, size_t size, bool fileio)
{
struct iio_dma_buffer_block *block;

@@ -171,13 +180,16 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
if (!block)
return NULL;

- block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
- &block->phys_addr, GFP_KERNEL);
- if (!block->vaddr) {
- kfree(block);
- return NULL;
+ if (fileio) {
+ block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
+ &block->phys_addr, GFP_KERNEL);
+ if (!block->vaddr) {
+ kfree(block);
+ return NULL;
+ }
}

+ block->fileio = fileio;
block->size = size;
block->state = IIO_BLOCK_STATE_DONE;
block->queue = queue;
@@ -186,6 +198,9 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(

iio_buffer_get(&queue->buffer);

+ if (!fileio)
+ atomic_inc(&queue->num_dmabufs);
+
return block;
}

@@ -218,13 +233,20 @@ void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
{
struct iio_dma_buffer_queue *queue = block->queue;
unsigned long flags;
+ bool cookie;
+
+ cookie = dma_fence_begin_signalling();

spin_lock_irqsave(&queue->list_lock, flags);
_iio_dma_buffer_block_done(block);
spin_unlock_irqrestore(&queue->list_lock, flags);

+ if (!block->fileio)
+ iio_buffer_signal_dmabuf_done(block->fence, 0);
+
iio_buffer_block_put_atomic(block);
iio_dma_buffer_queue_wake(queue);
+ dma_fence_end_signalling(cookie);
}
EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);

@@ -243,17 +265,27 @@ void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
{
struct iio_dma_buffer_block *block, *_block;
unsigned long flags;
+ bool cookie;
+
+ cookie = dma_fence_begin_signalling();

spin_lock_irqsave(&queue->list_lock, flags);
list_for_each_entry_safe(block, _block, list, head) {
list_del(&block->head);
block->bytes_used = 0;
_iio_dma_buffer_block_done(block);
+
+ if (!block->fileio)
+ iio_buffer_signal_dmabuf_done(block->fence, -EINTR);
iio_buffer_block_put_atomic(block);
}
spin_unlock_irqrestore(&queue->list_lock, flags);

+ if (queue->fileio.enabled)
+ queue->fileio.enabled = false;
+
iio_dma_buffer_queue_wake(queue);
+ dma_fence_end_signalling(cookie);
}
EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);

@@ -273,6 +305,16 @@ static bool iio_dma_block_reusable(struct iio_dma_buffer_block *block)
}
}

+static bool iio_dma_buffer_can_use_fileio(struct iio_dma_buffer_queue *queue)
+{
+ /*
+ * Note that queue->num_dmabufs cannot increase while the queue is
+ * locked, it can only decrease, so it does not race against
+ * iio_dma_buffer_alloc_block().
+ */
+ return queue->fileio.enabled || !atomic_read(&queue->num_dmabufs);
+}
+
/**
* iio_dma_buffer_request_update() - DMA buffer request_update callback
* @buffer: The buffer which to request an update
@@ -299,6 +341,12 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)

mutex_lock(&queue->lock);

+ queue->fileio.enabled = iio_dma_buffer_can_use_fileio(queue);
+
+ /* If DMABUFs were created, disable fileio interface */
+ if (!queue->fileio.enabled)
+ goto out_unlock;
+
/* Allocations are page aligned */
if (PAGE_ALIGN(queue->fileio.block_size) == PAGE_ALIGN(size))
try_reuse = true;
@@ -339,7 +387,7 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
}

if (!block) {
- block = iio_dma_buffer_alloc_block(queue, size);
+ block = iio_dma_buffer_alloc_block(queue, size, true);
if (!block) {
ret = -ENOMEM;
goto out_unlock;
@@ -412,8 +460,12 @@ static void iio_dma_buffer_submit_block(struct iio_dma_buffer_queue *queue,

block->state = IIO_BLOCK_STATE_ACTIVE;
iio_buffer_block_get(block);
+
ret = queue->ops->submit(queue, block);
if (ret) {
+ if (!block->fileio)
+ iio_buffer_signal_dmabuf_done(block->fence, ret);
+
/*
* This is a bit of a problem and there is not much we can do
* other then wait for the buffer to be disabled and re-enabled
@@ -646,6 +698,110 @@ size_t iio_dma_buffer_usage(struct iio_buffer *buf)
}
EXPORT_SYMBOL_GPL(iio_dma_buffer_usage);

+struct iio_dma_buffer_block *
+iio_dma_buffer_attach_dmabuf(struct iio_buffer *buffer,
+ struct dma_buf_attachment *attach)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ struct iio_dma_buffer_block *block;
+
+ guard(mutex)(&queue->lock);
+
+ /*
+ * If the buffer is enabled and in fileio mode new blocks can't be
+ * allocated.
+ */
+ if (queue->fileio.enabled)
+ return ERR_PTR(-EBUSY);
+
+ block = iio_dma_buffer_alloc_block(queue, attach->dmabuf->size, false);
+ if (!block)
+ return ERR_PTR(-ENOMEM);
+
+ /* Free memory that might be in use for fileio mode */
+ iio_dma_buffer_fileio_free(queue);
+
+ return block;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_attach_dmabuf);
+
+void iio_dma_buffer_detach_dmabuf(struct iio_buffer *buffer,
+ struct iio_dma_buffer_block *block)
+{
+ block->state = IIO_BLOCK_STATE_DEAD;
+ iio_buffer_block_put_atomic(block);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_detach_dmabuf);
+
+static int iio_dma_can_enqueue_block(struct iio_dma_buffer_block *block)
+{
+ struct iio_dma_buffer_queue *queue = block->queue;
+
+ /* If in fileio mode buffers can't be enqueued. */
+ if (queue->fileio.enabled)
+ return -EBUSY;
+
+ switch (block->state) {
+ case IIO_BLOCK_STATE_QUEUED:
+ return -EPERM;
+ case IIO_BLOCK_STATE_ACTIVE:
+ case IIO_BLOCK_STATE_DEAD:
+ return -EBUSY;
+ case IIO_BLOCK_STATE_DONE:
+ break;
+ }
+
+ return 0;
+}
+
+int iio_dma_buffer_enqueue_dmabuf(struct iio_buffer *buffer,
+ struct iio_dma_buffer_block *block,
+ struct dma_fence *fence,
+ struct sg_table *sgt,
+ size_t size, bool cyclic)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ bool cookie;
+ int ret;
+
+ WARN_ON(!mutex_is_locked(&queue->lock));
+
+ cookie = dma_fence_begin_signalling();
+
+ ret = iio_dma_can_enqueue_block(block);
+ if (ret < 0)
+ goto out_end_signalling;
+
+ block->bytes_used = size;
+ block->cyclic = cyclic;
+ block->sg_table = sgt;
+ block->fence = fence;
+
+ iio_dma_buffer_enqueue(queue, block);
+
+out_end_signalling:
+ dma_fence_end_signalling(cookie);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_enqueue_dmabuf);
+
+void iio_dma_buffer_lock_queue(struct iio_buffer *buffer)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+
+ mutex_lock(&queue->lock);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_lock_queue);
+
+void iio_dma_buffer_unlock_queue(struct iio_buffer *buffer)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+
+ mutex_unlock(&queue->lock);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_unlock_queue);
+
/**
* iio_dma_buffer_set_bytes_per_datum() - DMA buffer set_bytes_per_datum callback
* @buffer: Buffer to set the bytes-per-datum for
diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index 6e27e47077d5..5eb66a399002 100644
--- a/include/linux/iio/buffer-dma.h
+++ b/include/linux/iio/buffer-dma.h
@@ -7,6 +7,7 @@
#ifndef __INDUSTRIALIO_DMA_BUFFER_H__
#define __INDUSTRIALIO_DMA_BUFFER_H__

+#include <linux/atomic.h>
#include <linux/list.h>
#include <linux/kref.h>
#include <linux/spinlock.h>
@@ -16,6 +17,9 @@
struct iio_dma_buffer_queue;
struct iio_dma_buffer_ops;
struct device;
+struct dma_buf_attachment;
+struct dma_fence;
+struct sg_table;

/**
* enum iio_block_state - State of a struct iio_dma_buffer_block
@@ -41,6 +45,10 @@ enum iio_block_state {
* @queue: Parent DMA buffer queue
* @kref: kref used to manage the lifetime of block
* @state: Current state of the block
+ * @cyclic: True if this is a cyclic buffer
+ * @fileio: True if this buffer is used for fileio mode
+ * @sg_table: DMA table for the transfer when transferring a DMABUF
+ * @fence: DMA fence to be signaled when a DMABUF transfer is complete
*/
struct iio_dma_buffer_block {
/* May only be accessed by the owner of the block */
@@ -63,6 +71,12 @@ struct iio_dma_buffer_block {
* queue->list_lock if the block is not owned by the core.
*/
enum iio_block_state state;
+
+ bool cyclic;
+ bool fileio;
+
+ struct sg_table *sg_table;
+ struct dma_fence *fence;
};

/**
@@ -72,6 +86,7 @@ struct iio_dma_buffer_block {
* @pos: Read offset in the active block
* @block_size: Size of each block
* @next_dequeue: index of next block that will be dequeued
+ * @enabled: Whether the buffer is operating in fileio mode
*/
struct iio_dma_buffer_queue_fileio {
struct iio_dma_buffer_block *blocks[2];
@@ -80,6 +95,7 @@ struct iio_dma_buffer_queue_fileio {
size_t block_size;

unsigned int next_dequeue;
+ bool enabled;
};

/**
@@ -95,6 +111,7 @@ struct iio_dma_buffer_queue_fileio {
* the DMA controller
* @incoming: List of buffers on the incoming queue
* @active: Whether the buffer is currently active
+ * @num_dmabufs: Total number of DMABUFs attached to this queue
* @fileio: FileIO state
*/
struct iio_dma_buffer_queue {
@@ -107,6 +124,7 @@ struct iio_dma_buffer_queue {
struct list_head incoming;

bool active;
+ atomic_t num_dmabufs;

struct iio_dma_buffer_queue_fileio fileio;
};
@@ -144,4 +162,17 @@ int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue);
void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue);

+struct iio_dma_buffer_block *
+iio_dma_buffer_attach_dmabuf(struct iio_buffer *buffer,
+ struct dma_buf_attachment *attach);
+void iio_dma_buffer_detach_dmabuf(struct iio_buffer *buffer,
+ struct iio_dma_buffer_block *block);
+int iio_dma_buffer_enqueue_dmabuf(struct iio_buffer *buffer,
+ struct iio_dma_buffer_block *block,
+ struct dma_fence *fence,
+ struct sg_table *sgt,
+ size_t size, bool cyclic);
+void iio_dma_buffer_lock_queue(struct iio_buffer *buffer);
+void iio_dma_buffer_unlock_queue(struct iio_buffer *buffer);
+
#endif
--
2.43.0