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SubjectRe: [PATCH RFC 1/1] uio: Add dma-buf import ioctls
On Sat, Feb 23, 2019 at 12:28:17PM -0800, Hyun Kwon wrote:
> Add the dmabuf map / unmap interfaces. This allows the user driver
> to be able to import the external dmabuf and use it from user space.
>
> Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
> ---
> drivers/uio/Makefile | 2 +-
> drivers/uio/uio.c | 43 +++++++++
> drivers/uio/uio_dmabuf.c | 210 +++++++++++++++++++++++++++++++++++++++++++
> drivers/uio/uio_dmabuf.h | 26 ++++++
> include/uapi/linux/uio/uio.h | 33 +++++++
> 5 files changed, 313 insertions(+), 1 deletion(-)
> create mode 100644 drivers/uio/uio_dmabuf.c
> create mode 100644 drivers/uio/uio_dmabuf.h
> create mode 100644 include/uapi/linux/uio/uio.h
>
> diff --git a/drivers/uio/Makefile b/drivers/uio/Makefile
> index c285dd2..5da16c7 100644
> --- a/drivers/uio/Makefile
> +++ b/drivers/uio/Makefile
> @@ -1,5 +1,5 @@
> # SPDX-License-Identifier: GPL-2.0
> -obj-$(CONFIG_UIO) += uio.o
> +obj-$(CONFIG_UIO) += uio.o uio_dmabuf.o
> obj-$(CONFIG_UIO_CIF) += uio_cif.o
> obj-$(CONFIG_UIO_PDRV_GENIRQ) += uio_pdrv_genirq.o
> obj-$(CONFIG_UIO_DMEM_GENIRQ) += uio_dmem_genirq.o
> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
> index 1313422..6841f98 100644
> --- a/drivers/uio/uio.c
> +++ b/drivers/uio/uio.c
> @@ -24,6 +24,12 @@
> #include <linux/kobject.h>
> #include <linux/cdev.h>
> #include <linux/uio_driver.h>
> +#include <linux/list.h>
> +#include <linux/mutex.h>
> +
> +#include <uapi/linux/uio/uio.h>
> +
> +#include "uio_dmabuf.h"
>
> #define UIO_MAX_DEVICES (1U << MINORBITS)
>
> @@ -454,6 +460,8 @@ static irqreturn_t uio_interrupt(int irq, void *dev_id)
> struct uio_listener {
> struct uio_device *dev;
> s32 event_count;
> + struct list_head dbufs;
> + struct mutex dbufs_lock; /* protect @dbufs */
> };
>
> static int uio_open(struct inode *inode, struct file *filep)
> @@ -500,6 +508,9 @@ static int uio_open(struct inode *inode, struct file *filep)
> if (ret)
> goto err_infoopen;
>
> + INIT_LIST_HEAD(&listener->dbufs);
> + mutex_init(&listener->dbufs_lock);
> +
> return 0;
>
> err_infoopen:
> @@ -529,6 +540,10 @@ static int uio_release(struct inode *inode, struct file *filep)
> struct uio_listener *listener = filep->private_data;
> struct uio_device *idev = listener->dev;
>
> + ret = uio_dmabuf_cleanup(idev, &listener->dbufs, &listener->dbufs_lock);
> + if (ret)
> + dev_err(&idev->dev, "failed to clean up the dma bufs\n");
> +
> mutex_lock(&idev->info_lock);
> if (idev->info && idev->info->release)
> ret = idev->info->release(idev->info, inode);
> @@ -652,6 +667,33 @@ static ssize_t uio_write(struct file *filep, const char __user *buf,
> return retval ? retval : sizeof(s32);
> }
>
> +static long uio_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)

We have resisted adding a uio ioctl for a long time, can't you do this
through sysfs somehow?

A meta-comment about your ioctl structure:

> +#define UIO_DMABUF_DIR_BIDIR 1
> +#define UIO_DMABUF_DIR_TO_DEV 2
> +#define UIO_DMABUF_DIR_FROM_DEV 3
> +#define UIO_DMABUF_DIR_NONE 4

enumerated type?

> +
> +struct uio_dmabuf_args {
> + __s32 dbuf_fd;
> + __u64 dma_addr;
> + __u64 size;
> + __u32 dir;

Why the odd alignment? Are you sure this is the best packing for such a
structure?

Why is dbuf_fd __s32? dir can be __u8, right?

I don't know that dma layer very well, it would be good to get some
review from others to see if this really is even a viable thing to do.
The fd handling seems a bit "odd" here, but maybe I just do not
understand it.

thanks,

greg k-h

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