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[23.128.96.18]) by mx.google.com with ESMTP id cw5si2245729ejc.182.2021.02.14.07.28.41; Sun, 14 Feb 2021 07:29:05 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229829AbhBNPZY (ORCPT + 99 others); Sun, 14 Feb 2021 10:25:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:35896 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229783AbhBNPZX (ORCPT ); Sun, 14 Feb 2021 10:25:23 -0500 Received: from archlinux (cpc108967-cmbg20-2-0-cust86.5-4.cable.virginm.net [81.101.6.87]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 469AE64E61; Sun, 14 Feb 2021 15:24:38 +0000 (UTC) Date: Sun, 14 Feb 2021 15:24:33 +0000 From: Jonathan Cameron To: Alexandru Ardelean Cc: , , , , , Subject: Re: [PATCH v2 1/3] iio: core: Add mmap interface infrastructure Message-ID: <20210214152433.091ba147@archlinux> In-Reply-To: <20210212101143.18993-2-alexandru.ardelean@analog.com> References: <20210212101143.18993-1-alexandru.ardelean@analog.com> <20210212101143.18993-2-alexandru.ardelean@analog.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 12 Feb 2021 12:11:41 +0200 Alexandru Ardelean wrote: > From: Lars-Peter Clausen > > Add the necessary infrastructure to the IIO core to support an mmap based > interface to access the capture data. > > The advantage of the mmap based interface compared to the read() based > interface is that it avoids an extra copy of the data between kernel and > userspace. This is particular useful for high-speed devices which produce > several megabytes or even gigabytes of data per second. > > The data for the mmap interface is managed at the granularity of so called > blocks. A block is a contiguous region of memory (at the moment both > physically and virtually contiguous). Reducing the granularity from byte > level to block level is done to reduce the userspace-kernelspace > synchronization overhead since performing syscalls for each byte at a > data-rate of a few megabytes is not feasible. > > This of course leads to a slightly increased latency. For this reason an > application can choose the size of the blocks as well as how many blocks it > allocates. E.g. two blocks would be a traditional double buffering scheme. > But using a higher number might be necessary to avoid underflow/overflow > situations in the presence of scheduling latencies. > > A block can either be owned by kernel space or userspace. When owned by > userspace it save to access the data in the block and process it. When > owned by kernel space the block can be in one of 3 states. > > It can be in the incoming queue where all blocks submitted from userspace > are placed and are waiting to be processed by the kernel driver. > > It can be currently being processed by the kernel driver, this means it is > actively placing capturing data in it (usually using DMA). > > Or it can be in the outgoing queue where all blocks that have been > processed by the kernel are placed. Userspace can dequeue the blocks as > necessary. > > As part of the interface 5 new IOCTLs to manage the blocks and exchange > them between userspace and kernelspace. The IOCTLs can be accessed through > a open file descriptor to a IIO device. > > IIO_BUFFER_BLOCK_ALLOC_IOCTL(struct iio_buffer_block_alloc_req *): > Allocates new blocks. Can be called multiple times if necessary. A newly > allocated block is initially owned by userspace. > > IIO_BUFFER_BLOCK_FREE_IOCTL(void): > Frees all previously allocated blocks. If the backing memory of a block is > still in use by a kernel driver (i.e. active DMA transfer) it will be > freed once the kernel driver has released it. > > IIO_BUFFER_BLOCK_QUERY_IOCTL(struct iio_buffer_block *): > Queries information about a block. The id of the block about which > information is to be queried needs to be set by userspace. > > IIO_BUFFER_BLOCK_ENQUEUE_IOCTL(struct iio_buffer_block *): > Places a block on the incoming queue. This transfers ownership of the > block from userspace to kernelspace. Userspace must populate the id field > of the block to indicate which block to enqueue. > > IIO_BUFFER_BLOCK_DEQUEUE_IOCTL(struct iio_buffer_block *): > Removes the first block from the outgoing queue. This transfers ownership > of the block from kernelspace to userspace. Kernelspace will populate all > fields of the block. If the queue is empty and the file descriptor is set > to blocking the IOCTL will block until a new block is available on the > outgoing queue. > > To access the data stored in a block by userspace the block must be mapped > to the process's memory. This is done by calling mmap() on the IIO device > file descriptor. Each block has a unique offset assigned to it which should > be passed to the mmap interface. E.g. > > mmap(0, block.size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, > block.offset); > > A typical workflow for the new interface is: > > BLOCK_ALLOC > > foreach block > BLOCK_QUERY block > mmap block.data.offset > BLOCK_ENQUEUE block > > enable buffer > > while !done > BLOCK_DEQUEUE block > process data > BLOCK_ENQUEUE block > > disable buffer > > BLOCK_FREE Rather feels like some of this info should be in the formal docs somewhere rather than just burried in this patch description. Also good to have a bit more in the way of docs in the uapi header. > > Signed-off-by: Lars-Peter Clausen > Signed-off-by: Alexandru Ardelean Few trivial things inline, but otherwise seems like straightforwards wrappers. Jonathan > --- > drivers/iio/industrialio-buffer.c | 157 ++++++++++++++++++++++++++++++ > include/linux/iio/buffer-dma.h | 5 - > include/linux/iio/buffer_impl.h | 23 +++++ > include/uapi/linux/iio/buffer.h | 26 +++++ > 4 files changed, 206 insertions(+), 5 deletions(-) > > diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c > index 3aa6702a5811..50228df0b09f 100644 > --- a/drivers/iio/industrialio-buffer.c > +++ b/drivers/iio/industrialio-buffer.c > @@ -16,6 +16,7 @@ > #include > #include > #include > +#include > #include > #include > > @@ -1370,6 +1371,12 @@ static void iio_buffer_unregister_legacy_sysfs_groups(struct iio_dev *indio_dev) > kfree(iio_dev_opaque->legacy_scan_el_group.attrs); > } > > +static void iio_buffer_free_blocks(struct iio_buffer *buffer) > +{ > + if (buffer->access->free_blocks) > + buffer->access->free_blocks(buffer); > +} > + > static int iio_buffer_chrdev_release(struct inode *inode, struct file *filep) > { > struct iio_dev_buffer_pair *ib = filep->private_data; > @@ -1378,18 +1385,24 @@ static int iio_buffer_chrdev_release(struct inode *inode, struct file *filep) > > wake_up(&buffer->pollq); > clear_bit(IIO_BUSY_BIT_POS, &buffer->flags); > + iio_buffer_free_blocks(buffer); > iio_device_put(indio_dev); > kfree(ib); > > return 0; > } > > +static long iio_buffer_ioctl(struct file *filep, unsigned int cmd, unsigned long arg); > +static int iio_buffer_mmap(struct file *filep, struct vm_area_struct *vma); > + > static const struct file_operations iio_buffer_chrdev_fileops = { > .owner = THIS_MODULE, > .llseek = noop_llseek, > .read = iio_buffer_read, > .poll = iio_buffer_poll, > + .unlocked_ioctl = iio_buffer_ioctl, > .compat_ioctl = compat_ptr_ioctl, Why do we have an existing compat_ioctl here? Seems odd without the unlocked_ioctl. I see introduced in the multi buffer series whereas I think it should in this one. It has a test against being there without the unlocked_ioctl though so no great disaster. > + .mmap = iio_buffer_mmap, > .release = iio_buffer_chrdev_release, > }; > > @@ -1762,6 +1775,150 @@ void iio_buffer_put(struct iio_buffer *buffer) > } > EXPORT_SYMBOL_GPL(iio_buffer_put); > > +static int iio_buffer_query_block(struct iio_buffer *buffer, > + struct iio_buffer_block __user *user_block) > +{ > + struct iio_buffer_block block; > + int ret; > + > + if (!buffer->access->query_block) > + return -ENOSYS; > + > + if (copy_from_user(&block, user_block, sizeof(block))) > + return -EFAULT; > + > + ret = buffer->access->query_block(buffer, &block); > + if (ret) > + return ret; > + > + if (copy_to_user(user_block, &block, sizeof(block))) > + return -EFAULT; > + > + return 0; > +} > + > +static int iio_buffer_dequeue_block(struct iio_dev *indio_dev, > + struct iio_buffer *buffer, > + struct iio_buffer_block __user *user_block, > + bool non_blocking) > +{ > + struct iio_buffer_block block; > + int ret; > + > + if (!buffer->access->dequeue_block) > + return -ENOSYS; > + > + do { > + if (!iio_buffer_data_available(buffer)) { > + if (non_blocking) > + return -EAGAIN; > + > + ret = wait_event_interruptible(buffer->pollq, > + iio_buffer_data_available(buffer) || > + indio_dev->info == NULL); > + if (ret) > + return ret; > + if (indio_dev->info == NULL) > + return -ENODEV; > + } > + > + ret = buffer->access->dequeue_block(buffer, &block); > + if (ret == -EAGAIN && non_blocking) > + ret = 0; > + } while (ret); > + > + if (ret) > + return ret; > + > + if (copy_to_user(user_block, &block, sizeof(block))) > + return -EFAULT; > + > + return 0; > +} > + > +static int iio_buffer_enqueue_block(struct iio_buffer *buffer, > + struct iio_buffer_block __user *user_block) > +{ > + struct iio_buffer_block block; > + > + if (!buffer->access->enqueue_block) > + return -ENOSYS; > + > + if (copy_from_user(&block, user_block, sizeof(block))) > + return -EFAULT; > + > + return buffer->access->enqueue_block(buffer, &block); > +} > + > +static int iio_buffer_alloc_blocks(struct iio_buffer *buffer, > + struct iio_buffer_block_alloc_req __user *user_req) > +{ > + struct iio_buffer_block_alloc_req req; > + int ret; > + > + if (!buffer->access->alloc_blocks) > + return -ENOSYS; > + > + if (copy_from_user(&req, user_req, sizeof(req))) > + return -EFAULT; > + > + ret = buffer->access->alloc_blocks(buffer, &req); > + if (ret) > + return ret; > + > + if (copy_to_user(user_req, &req, sizeof(req))) > + return -EFAULT; > + > + return 0; > +} > + > +static long iio_buffer_ioctl(struct file *filep, unsigned int cmd, unsigned long arg) > +{ > + bool non_blocking = filep->f_flags & O_NONBLOCK; > + struct iio_dev_buffer_pair *ib = filep->private_data; > + struct iio_dev *indio_dev = ib->indio_dev; > + struct iio_buffer *buffer = ib->buffer; > + > + if (!buffer || !buffer->access) > + return -ENODEV; > + > + switch (cmd) { > + case IIO_BUFFER_BLOCK_ALLOC_IOCTL: > + return iio_buffer_alloc_blocks(buffer, > + (struct iio_buffer_block_alloc_req __user *)arg); > + case IIO_BUFFER_BLOCK_FREE_IOCTL: > + iio_buffer_free_blocks(buffer); > + return 0; > + case IIO_BUFFER_BLOCK_QUERY_IOCTL: > + return iio_buffer_query_block(buffer, > + (struct iio_buffer_block __user *)arg); > + case IIO_BUFFER_BLOCK_ENQUEUE_IOCTL: > + return iio_buffer_enqueue_block(buffer, > + (struct iio_buffer_block __user *)arg); > + case IIO_BUFFER_BLOCK_DEQUEUE_IOCTL: > + return iio_buffer_dequeue_block(indio_dev, buffer, > + (struct iio_buffer_block __user *)arg, non_blocking); > + } > + return -EINVAL; > +} > + > +static int iio_buffer_mmap(struct file *filep, struct vm_area_struct *vma) > +{ > + struct iio_dev_buffer_pair *ib = filep->private_data; > + struct iio_buffer *buffer = ib->buffer; > + > + if (!buffer->access || !buffer->access->mmap) > + return -ENODEV; > + > + if (!(vma->vm_flags & VM_SHARED)) > + return -EINVAL; > + > + if (!(vma->vm_flags & VM_READ)) > + return -EINVAL; > + > + return buffer->access->mmap(buffer, vma); > +} > + > /** > * iio_device_attach_buffer - Attach a buffer to a IIO device > * @indio_dev: The device the buffer should be attached to > diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h > index ff15c61bf319..6564bdcdac66 100644 > --- a/include/linux/iio/buffer-dma.h > +++ b/include/linux/iio/buffer-dma.h > @@ -17,11 +17,6 @@ struct iio_dma_buffer_queue; > struct iio_dma_buffer_ops; > struct device; > > -struct iio_buffer_block { > - u32 size; > - u32 bytes_used; > -}; > - > /** > * enum iio_block_state - State of a struct iio_dma_buffer_block > * @IIO_BLOCK_STATE_DEQUEUED: Block is not queued > diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h > index 245b32918ae1..1d57dc7ccb4f 100644 > --- a/include/linux/iio/buffer_impl.h > +++ b/include/linux/iio/buffer_impl.h > @@ -34,6 +34,18 @@ struct iio_buffer; > * device stops sampling. Calles are balanced with @enable. > * @release: called when the last reference to the buffer is dropped, > * should free all resources allocated by the buffer. > + * @alloc_blocks: called from userspace via ioctl to allocate blocks > + * that will be used via the mmap interface. > + * @free_blocks: called from userspace via ioctl to free all blocks > + * allocated for this buffer. > + * @enqueue_block: called from userspace via ioctl to queue this block > + * to this buffer. Requires a valid block id. > + * @dequeue_block: called from userspace via ioctl to dequeue this block > + * from this buffer. Requires a valid block id. > + * @query_block: called from userspace via ioctl to query the attributes > + * of this block. Requires a valid block id. > + * @mmap: mmap hook for this buffer. Userspace mmap() calls will > + * get routed to this. > * @modes: Supported operating modes by this buffer type > * @flags: A bitmask combination of INDIO_BUFFER_FLAG_* > * > @@ -60,6 +72,17 @@ struct iio_buffer_access_funcs { > > void (*release)(struct iio_buffer *buffer); > > + int (*alloc_blocks)(struct iio_buffer *buffer, > + struct iio_buffer_block_alloc_req *req); > + int (*free_blocks)(struct iio_buffer *buffer); > + int (*enqueue_block)(struct iio_buffer *buffer, > + struct iio_buffer_block *block); > + int (*dequeue_block)(struct iio_buffer *buffer, > + struct iio_buffer_block *block); > + int (*query_block)(struct iio_buffer *buffer, > + struct iio_buffer_block *block); > + int (*mmap)(struct iio_buffer *buffer, struct vm_area_struct *vma); > + > unsigned int modes; > unsigned int flags; > }; > diff --git a/include/uapi/linux/iio/buffer.h b/include/uapi/linux/iio/buffer.h > index 13939032b3f6..70ad3aea01ea 100644 > --- a/include/uapi/linux/iio/buffer.h > +++ b/include/uapi/linux/iio/buffer.h > @@ -5,6 +5,32 @@ > #ifndef _UAPI_IIO_BUFFER_H_ > #define _UAPI_IIO_BUFFER_H_ > > +struct iio_buffer_block_alloc_req { > + __u32 type; > + __u32 size; > + __u32 count; > + __u32 id; > +}; > + > +#define IIO_BUFFER_BLOCK_FLAG_TIMESTAMP_VALID (1 << 0) > + Add some docs for the elements of these structures. > +struct iio_buffer_block { > + __u32 id; > + __u32 size; > + __u32 bytes_used; > + __u32 type; > + __u32 flags; > + union { > + __u32 offset; > + } data; > + __u64 timestamp; > +}; > + > #define IIO_BUFFER_GET_FD_IOCTL _IOWR('i', 0x91, int) > +#define IIO_BUFFER_BLOCK_ALLOC_IOCTL _IOWR('i', 0x92, struct iio_buffer_block_alloc_req) > +#define IIO_BUFFER_BLOCK_FREE_IOCTL _IO('i', 0x93) > +#define IIO_BUFFER_BLOCK_QUERY_IOCTL _IOWR('i', 0x93, struct iio_buffer_block) > +#define IIO_BUFFER_BLOCK_ENQUEUE_IOCTL _IOWR('i', 0x94, struct iio_buffer_block) > +#define IIO_BUFFER_BLOCK_DEQUEUE_IOCTL _IOWR('i', 0x95, struct iio_buffer_block) > > #endif /* _UAPI_IIO_BUFFER_H_ */