[PATCH v4 5/6] iio: buffer-dma: Add mmap support

From: Alexandru Ardelean
Date: Wed Feb 17 2021 - 02:40:23 EST

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From: Lars-Peter Clausen <lars@xxxxxxxxxx>

Add support for the new mmap interface to IIO DMA buffer. This interface
allows to directly map the backing memory of a block to userspace. This is
especially advantageous for high-speed devices where the extra copy from
kernel space to userspace of the data incurs a significant overhead.

In addition this interface allows more fine grained control over how many
blocks are allocated and their size.

Signed-off-by: Lars-Peter Clausen <lars@xxxxxxxxxx>
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
---
drivers/iio/buffer/industrialio-buffer-dma.c | 279 +++++++++++++++++-
.../buffer/industrialio-buffer-dmaengine.c | 22 +-
include/linux/iio/buffer-dma.h | 22 +-
3 files changed, 306 insertions(+), 17 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index 858af7eea53e..e187c1640b17 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -90,6 +90,9 @@
* callback is called from within the custom callback.
*/

+static unsigned int iio_dma_buffer_max_block_size = SZ_16M;
+module_param_named(max_block_size, iio_dma_buffer_max_block_size, uint, 0644);
+
static void iio_buffer_block_release(struct kref *kref)
{
struct iio_dma_buffer_block *block = container_of(kref,
@@ -97,7 +100,7 @@ static void iio_buffer_block_release(struct kref *kref)

WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);

- dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
+ dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->block.size),
block->vaddr, block->phys_addr);

iio_buffer_put(&block->queue->buffer);
@@ -178,7 +181,7 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
return NULL;
}

- block->size = size;
+ block->block.size = size;
block->state = IIO_BLOCK_STATE_DEQUEUED;
block->queue = queue;
INIT_LIST_HEAD(&block->head);
@@ -243,7 +246,7 @@ void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
spin_lock_irqsave(&queue->list_lock, flags);
list_for_each_entry_safe(block, _block, list, head) {
list_del(&block->head);
- block->bytes_used = 0;
+ block->block.bytes_used = 0;
_iio_dma_buffer_block_done(block);
iio_buffer_block_put_atomic(block);
}
@@ -296,6 +299,10 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)

mutex_lock(&queue->lock);

+ /* If in mmap mode dont do anything */
+ if (queue->num_blocks)
+ goto out_unlock;
+
/* Allocations are page aligned */
if (PAGE_ALIGN(queue->fileio.block_size) == PAGE_ALIGN(size))
try_reuse = true;
@@ -330,7 +337,7 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
iio_buffer_block_put(block);
block = NULL;
} else {
- block->size = size;
+ block->block.size = size;
}
} else {
block = NULL;
@@ -345,6 +352,8 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
queue->fileio.blocks[i] = block;
}

+ block->block.id = i;
+
block->state = IIO_BLOCK_STATE_QUEUED;
list_add_tail(&block->head, &queue->incoming);
}
@@ -428,6 +437,7 @@ int iio_dma_buffer_enable(struct iio_buffer *buffer,
struct iio_dma_buffer_block *block, *_block;

mutex_lock(&queue->lock);
+ queue->fileio.enabled = !queue->num_blocks;
queue->active = true;
list_for_each_entry_safe(block, _block, &queue->incoming, head) {
list_del(&block->head);
@@ -453,6 +463,7 @@ int iio_dma_buffer_disable(struct iio_buffer *buffer,
struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);

mutex_lock(&queue->lock);
+ queue->fileio.enabled = false;
queue->active = false;

if (queue->ops && queue->ops->abort)
@@ -514,6 +525,11 @@ int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,

mutex_lock(&queue->lock);

+ if (!queue->fileio.enabled) {
+ ret = -EBUSY;
+ goto out_unlock;
+ }
+
if (!queue->fileio.active_block) {
block = iio_dma_buffer_dequeue(queue);
if (block == NULL) {
@@ -527,8 +543,8 @@ int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,
}

n = rounddown(n, buffer->bytes_per_datum);
- if (n > block->bytes_used - queue->fileio.pos)
- n = block->bytes_used - queue->fileio.pos;
+ if (n > block->block.bytes_used - queue->fileio.pos)
+ n = block->block.bytes_used - queue->fileio.pos;

if (copy_to_user(user_buffer, block->vaddr + queue->fileio.pos, n)) {
ret = -EFAULT;
@@ -537,7 +553,7 @@ int iio_dma_buffer_read(struct iio_buffer *buffer, size_t n,

queue->fileio.pos += n;

- if (queue->fileio.pos == block->bytes_used) {
+ if (queue->fileio.pos == block->block.bytes_used) {
queue->fileio.active_block = NULL;
iio_dma_buffer_enqueue(queue, block);
}
@@ -573,11 +589,11 @@ size_t iio_dma_buffer_data_available(struct iio_buffer *buf)

mutex_lock(&queue->lock);
if (queue->fileio.active_block)
- data_available += queue->fileio.active_block->size;
+ data_available += queue->fileio.active_block->block.size;

spin_lock_irq(&queue->list_lock);
list_for_each_entry(block, &queue->outgoing, head)
- data_available += block->size;
+ data_available += block->block.size;
spin_unlock_irq(&queue->list_lock);
mutex_unlock(&queue->lock);

@@ -585,6 +601,251 @@ size_t iio_dma_buffer_data_available(struct iio_buffer *buf)
}
EXPORT_SYMBOL_GPL(iio_dma_buffer_data_available);

+int iio_dma_buffer_alloc_blocks(struct iio_buffer *buffer,
+ struct iio_buffer_block_alloc_req *req)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ struct iio_dma_buffer_block **blocks;
+ unsigned int num_blocks;
+ unsigned int i;
+ int ret = 0;
+
+ mutex_lock(&queue->lock);
+
+ /*
+ * If the buffer is enabled and in fileio mode new blocks can't be
+ * allocated.
+ */
+ if (queue->fileio.enabled) {
+ ret = -EBUSY;
+ goto err_unlock;
+ }
+
+ /* Free memory that might be in use for fileio mode */
+ iio_dma_buffer_fileio_free(queue);
+
+ /* 64 blocks ought to be enough for anybody ;) */
+ if (req->count > 64 - queue->num_blocks)
+ req->count = 64 - queue->num_blocks;
+ if (req->size > iio_dma_buffer_max_block_size)
+ req->size = iio_dma_buffer_max_block_size;
+
+ req->id = queue->num_blocks;
+
+ if (req->count == 0 || req->size == 0) {
+ ret = 0;
+ goto err_unlock;
+ }
+
+ num_blocks = req->count + queue->num_blocks;
+
+ blocks = krealloc(queue->blocks, sizeof(*blocks) * num_blocks,
+ GFP_KERNEL);
+ if (!blocks) {
+ ret = -ENOMEM;
+ goto err_unlock;
+ }
+
+ for (i = queue->num_blocks; i < num_blocks; i++) {
+ blocks[i] = iio_dma_buffer_alloc_block(queue, req->size);
+ if (!blocks[i]) {
+ ret = -ENOMEM;
+ goto err_unwind;
+ }
+ blocks[i]->block.id = i;
+ blocks[i]->block.data.offset = queue->max_offset;
+ queue->max_offset += PAGE_ALIGN(req->size);
+ }
+
+ req->count = i - queue->num_blocks;
+ queue->num_blocks = i;
+ queue->blocks = blocks;
+
+ mutex_unlock(&queue->lock);
+
+ return 0;
+
+err_unwind:
+ for (; i >= 0; i--)
+ iio_buffer_block_put(blocks[i]);
+ kfree(blocks);
+err_unlock:
+ mutex_unlock(&queue->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_alloc_blocks);
+
+int iio_dma_buffer_free_blocks(struct iio_buffer *buffer)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ unsigned int i;
+
+ mutex_lock(&queue->lock);
+
+ spin_lock_irq(&queue->list_lock);
+ INIT_LIST_HEAD(&queue->incoming);
+ INIT_LIST_HEAD(&queue->outgoing);
+
+ for (i = 0; i < queue->num_blocks; i++)
+ queue->blocks[i]->state = IIO_BLOCK_STATE_DEAD;
+ spin_unlock_irq(&queue->list_lock);
+
+ for (i = 0; i < queue->num_blocks; i++)
+ iio_buffer_block_put(queue->blocks[i]);
+
+ kfree(queue->blocks);
+ queue->blocks = NULL;
+ queue->num_blocks = 0;
+ queue->max_offset = 0;
+
+ mutex_unlock(&queue->lock);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_free_blocks);
+
+int iio_dma_buffer_query_block(struct iio_buffer *buffer,
+ struct iio_buffer_block *block)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ int ret = 0;
+
+ mutex_lock(&queue->lock);
+
+ if (block->id >= queue->num_blocks) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ *block = queue->blocks[block->id]->block;
+
+out_unlock:
+ mutex_unlock(&queue->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_query_block);
+
+int iio_dma_buffer_enqueue_block(struct iio_buffer *buffer,
+ struct iio_buffer_block *block)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ struct iio_dma_buffer_block *dma_block;
+ int ret = 0;
+
+ mutex_lock(&queue->lock);
+
+ if (block->id >= queue->num_blocks) {
+ ret = -EINVAL;
+ goto out_unlock;
+ }
+
+ dma_block = queue->blocks[block->id];
+ dma_block->block.bytes_used = block->bytes_used;
+ dma_block->block.flags = block->flags;
+
+ switch (dma_block->state) {
+ case IIO_BLOCK_STATE_DONE:
+ list_del_init(&dma_block->head);
+ break;
+ case IIO_BLOCK_STATE_QUEUED:
+ /* Nothing to do */
+ goto out_unlock;
+ case IIO_BLOCK_STATE_DEQUEUED:
+ break;
+ default:
+ ret = -EBUSY;
+ goto out_unlock;
+ }
+
+ iio_dma_buffer_enqueue(queue, dma_block);
+
+out_unlock:
+ mutex_unlock(&queue->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_enqueue_block);
+
+int iio_dma_buffer_dequeue_block(struct iio_buffer *buffer,
+ struct iio_buffer_block *block)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ struct iio_dma_buffer_block *dma_block;
+ int ret = 0;
+
+ mutex_lock(&queue->lock);
+
+ dma_block = iio_dma_buffer_dequeue(queue);
+ if (!dma_block) {
+ ret = -EAGAIN;
+ goto out_unlock;
+ }
+
+ *block = dma_block->block;
+
+out_unlock:
+ mutex_unlock(&queue->lock);
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_dequeue_block);
+
+static void iio_dma_buffer_mmap_open(struct vm_area_struct *area)
+{
+ struct iio_dma_buffer_block *block = area->vm_private_data;
+
+ iio_buffer_block_get(block);
+}
+
+static void iio_dma_buffer_mmap_close(struct vm_area_struct *area)
+{
+ struct iio_dma_buffer_block *block = area->vm_private_data;
+
+ iio_buffer_block_put(block);
+}
+
+static const struct vm_operations_struct iio_dma_buffer_vm_ops = {
+ .open = iio_dma_buffer_mmap_open,
+ .close = iio_dma_buffer_mmap_close,
+};
+
+int iio_dma_buffer_mmap(struct iio_buffer *buffer, struct vm_area_struct *vma)
+{
+ struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+ struct iio_dma_buffer_block *block = NULL;
+ size_t vm_offset;
+ unsigned int i;
+
+ vm_offset = vma->vm_pgoff << PAGE_SHIFT;
+
+ for (i = 0; i < queue->num_blocks; i++) {
+ if (queue->blocks[i]->block.data.offset == vm_offset) {
+ block = queue->blocks[i];
+ break;
+ }
+ }
+
+ if (block == NULL)
+ return -EINVAL;
+
+ if (PAGE_ALIGN(block->block.size) < vma->vm_end - vma->vm_start)
+ return -EINVAL;
+
+ vma->vm_pgoff = 0;
+
+ vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
+ vma->vm_ops = &iio_dma_buffer_vm_ops;
+ vma->vm_private_data = block;
+
+ vma->vm_ops->open(vma);
+
+ return dma_mmap_coherent(queue->dev, vma, block->vaddr,
+ block->phys_addr, vma->vm_end - vma->vm_start);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_mmap);
+
/**
* 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/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
index 19fbe5d9ef5b..6db24be7e11d 100644
--- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
+++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
@@ -54,7 +54,7 @@ static void iio_dmaengine_buffer_block_done(void *data,
spin_lock_irqsave(&block->queue->list_lock, flags);
list_del(&block->head);
spin_unlock_irqrestore(&block->queue->list_lock, flags);
- block->bytes_used -= result->residue;
+ block->block.bytes_used -= result->residue;
iio_dma_buffer_block_done(block);
}

@@ -66,12 +66,17 @@ static int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
struct dma_async_tx_descriptor *desc;
dma_cookie_t cookie;

- block->bytes_used = min(block->size, dmaengine_buffer->max_size);
- block->bytes_used = rounddown(block->bytes_used,
- dmaengine_buffer->align);
+ block->block.bytes_used = min(block->block.size,
+ dmaengine_buffer->max_size);
+ block->block.bytes_used = rounddown(block->block.bytes_used,
+ dmaengine_buffer->align);
+ if (block->block.bytes_used == 0) {
+ iio_dma_buffer_block_done(block);
+ return 0;
+ }

desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
- block->phys_addr, block->bytes_used, DMA_DEV_TO_MEM,
+ block->phys_addr, block->block.bytes_used, DMA_DEV_TO_MEM,
DMA_PREP_INTERRUPT);
if (!desc)
return -ENOMEM;
@@ -120,6 +125,13 @@ static const struct iio_buffer_access_funcs iio_dmaengine_buffer_ops = {
.data_available = iio_dma_buffer_data_available,
.release = iio_dmaengine_buffer_release,

+ .alloc_blocks = iio_dma_buffer_alloc_blocks,
+ .free_blocks = iio_dma_buffer_free_blocks,
+ .query_block = iio_dma_buffer_query_block,
+ .enqueue_block = iio_dma_buffer_enqueue_block,
+ .dequeue_block = iio_dma_buffer_dequeue_block,
+ .mmap = iio_dma_buffer_mmap,
+
.modes = INDIO_BUFFER_HARDWARE,
.flags = INDIO_BUFFER_FLAG_FIXED_WATERMARK,
};
diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index 9de27d23e791..f6f2ce3e2ed1 100644
--- a/include/linux/iio/buffer-dma.h
+++ b/include/linux/iio/buffer-dma.h
@@ -36,7 +36,7 @@ enum iio_block_state {
/**
* struct iio_dma_buffer_block - IIO buffer block
* @head: List head
- * @size: Total size of the block in bytes
+ * @block: Underlying block object for this DMA buffer block
* @bytes_used: Number of bytes that contain valid data
* @vaddr: Virutal address of the blocks memory
* @phys_addr: Physical address of the blocks memory
@@ -47,7 +47,7 @@ enum iio_block_state {
struct iio_dma_buffer_block {
/* May only be accessed by the owner of the block */
struct list_head head;
- size_t bytes_used;
+ struct iio_buffer_block block;

/*
* Set during allocation, constant thereafter. May be accessed read-only
@@ -55,7 +55,6 @@ struct iio_dma_buffer_block {
*/
void *vaddr;
dma_addr_t phys_addr;
- u32 size;
struct iio_dma_buffer_queue *queue;

/* Must not be accessed outside the core. */
@@ -73,12 +72,14 @@ struct iio_dma_buffer_block {
* @active_block: Block being used in read()
* @pos: Read offset in the active block
* @block_size: Size of each block
+ * @enabled: Whether the buffer is operating in fileio mode
*/
struct iio_dma_buffer_queue_fileio {
struct iio_dma_buffer_block *blocks[2];
struct iio_dma_buffer_block *active_block;
size_t pos;
size_t block_size;
+ bool enabled;
};

/**
@@ -109,6 +110,10 @@ struct iio_dma_buffer_queue {

bool active;

+ unsigned int num_blocks;
+ struct iio_dma_buffer_block **blocks;
+ unsigned int max_offset;
+
struct iio_dma_buffer_queue_fileio fileio;
};

@@ -143,4 +148,15 @@ 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);

+int iio_dma_buffer_alloc_blocks(struct iio_buffer *buffer,
+ struct iio_buffer_block_alloc_req *req);
+int iio_dma_buffer_free_blocks(struct iio_buffer *buffer);
+int iio_dma_buffer_query_block(struct iio_buffer *buffer,
+ struct iio_buffer_block *block);
+int iio_dma_buffer_enqueue_block(struct iio_buffer *buffer,
+ struct iio_buffer_block *block);
+int iio_dma_buffer_dequeue_block(struct iio_buffer *buffer,
+ struct iio_buffer_block *block);
+int iio_dma_buffer_mmap(struct iio_buffer *buffer, struct vm_area_struct *vma);
+
#endif
--
2.17.1

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