Date:   Tue, 18 Feb 2020 20:34:00 -0800
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Vitor Soares <Vitor.Soares@...opsys.com>,
        linux-kernel@...r.kernel.org, linux-i3c@...ts.infradead.org
Cc:     Joao.Pinto@...opsys.com, Jose.Abreu@...opsys.com,
        bbrezillon@...nel.org, gregkh@...uxfoundation.org,
        wsa@...-dreams.de, arnd@...db.de, broonie@...nel.org,
        corbet@....net
Subject: Re: [PATCH v3 5/5] add i3cdev documentation

On 2/18/20 4:20 PM, Vitor Soares wrote:
> This patch add documentation for the userspace API of i3cdev module.
> 
> Signed-off-by: Vitor Soares <vitor.soares@...opsys.com>
> ---
>  Documentation/userspace-api/i3c/i3cdev.rst | 116 +++++++++++++++++++++++++++++
>  1 file changed, 116 insertions(+)
>  create mode 100644 Documentation/userspace-api/i3c/i3cdev.rst
> 
> diff --git a/Documentation/userspace-api/i3c/i3cdev.rst b/Documentation/userspace-api/i3c/i3cdev.rst
> new file mode 100644
> index 0000000..ada269f
> --- /dev/null
> +++ b/Documentation/userspace-api/i3c/i3cdev.rst
> @@ -0,0 +1,116 @@
> +====================
> +I3C Device Interface
> +====================
> +
> +I3C devices have the flexibility of being accessed from userspace, as well
> +through the conventional use of kernel drivers. Userspace access, although
> +limited to private SDR I3C transfers, provides the advantage of simplifying
> +the implementation of straightforward communication protocols, applicable to
> +scenarios where transfers are dedicated such for sensor bring-up scenarios
> +(prototyping environments) or for microcontroller slave communication
> +implementation.
> +
> +The major device number is dynamically attributed and it's all reserved for

                                          allocated (?)

> +the i3c devices. By default, the i3cdev module only exposes the i3c devices

       I3C                                                         I3C

> +without device driver bind and aren't of master type in sort of character
> +device file under /dev/bus/i3c/ folder. They are identified through its

IMO:                              s/folder/directory/ or sub-directory

> +<bus id>-<Provisional ID> same way they can be found in /sys/bus/i3c/devices/.

                             in the same way

> +::
> +
> +# ls -l /dev/bus/i3c/
> +total 0
> +crw-------    1 root     root      248,   0 Jan  1 00:22 0-6072303904d2
> +crw-------    1 root     root      248,   1 Jan  1 00:22 0-b7405ba00929
> +
> +The simplest way to use this interface is to not have an I3C device bound to
> +a kernel driver, this can be achieved by not have the kernel driver loaded or

            driver. This                 by not having

> +using the Sysfs to unbind the kernel driver from the device.

         the sysfs interface to unbind

> +
> +BASIC CHARACTER DEVICE API
> +===============================
> +For now, the API has only support private SDR read and write transfers.

                        only support for private

For the unfamiliar, what is this "SDR"?  (thanks)

> +Those transaction can be achieved by the following:
> +
> +``read(file, buffer, sizeof(buffer))``
> +  The standard read() operation will work as a simple transaction of private
> +  SDR read data followed a stop.
> +  Return the number of bytes read on success, and a negative error otherwise.
> +
> +``write(file, buffer, sizeof(buffer))``
> +  The standard write() operation will work as a simple transaction of private
> +  SDR write data followed a stop.
> +  Return the number of bytes written on success, and a negative error otherwise.
> +
> +``ioctl(file, I3C_IOC_PRIV_XFER(nxfers), struct i3c_ioc_priv_xfer *xfers)``
> +  It combines read/write transactions without a stop in between.
> +  Return 0 on success, and a negative error otherwise.
> +
> +NOTES:
> +  - According to the MIPI I3C Protocol is the I3C slave that terminates the read

                                          it is the I3C slave

> +    transaction otherwise Master can abort early on ninth (T) data bit of each
> +    SDR data word.
> +
> +  - Normal open() and close() operations on /dev/bus/i3c/<bus>-<provisional id>
> +    files work as you would expect.
> +
> +  - As documented in cdev_del() if a device was already open during
> +    i3cdev_detach, the read(), write() and ioctl() fops will still be callable
> +    yet they will return -EACCES.
> +
> +C EXAMPLE
> +=========
> +Working with I3C devices is much like working with files. You will need to open
> +a file descriptor, do some I/O operations with it, and then close it.
> +
> +The following header files should be included in an I3C program::
> +
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <sys/ioctl.h>
> +#include <linux/types.h>
> +#include <linux/i3c/i3cdev.h>
> +
> +To work with an I3C device, the application must open the driver, made
> +available at the device node::
> +
> +  int file;
> +
> +  file = open("/dev/bus/i3c/0-6072303904d2", O_RDWR);
> +  if (file < 0)
> +  exit(1);

better indentation?

> +
> +Now the file is opened, we can perform the operations available::
> +
> +  /* Write function */
> +  uint_t8  buf[] = {0x00, 0xde, 0xad, 0xbe, 0xef}

I can't find uint_t8.  Where is it located?
and the braces should end with a ';'.

> +  if (write(file, buf, 5) != 5) {
> +    /* ERROR HANDLING: I3C transaction failed */
> +  }
> +
> +  /*  Read function */
> +  ret = read(file, buf, 5);
> +  If (ret < 0) {
> +    /* ERROR HANDLING: I3C transaction failed */
> +  } else {
> +    /* Iterate over buf[] to get the read data */
> +  }
> +
> +  /* IOCTL function */
> +  struct i3c_ioc_priv_xfer xfers[2];
> +
> +  uint8_t tx_buf[] = {0x00, 0xde, 0xad, 0xbe, 0xef};
> +  uint8_t rx_buf[10];
> +
> +  xfers[0].data = (uintptr_t)tx_buf;
> +  xfers[0].len = 5;
> +  xfers[0].rnw = 0;
> +  xfers[1].data = (uintptr_t)rx_buf;
> +  xfers[1].len = 10;
> +  xfers[1].rnw = 1;
> +
> +  if (ioctl(file, I3C_IOC_PRIV_XFER(2), xfers) < 0)
> +    /* ERROR HANDLING: I3C transaction failed */
> +
> +The device can be closed when the open file descriptor is no longer required::
> +
> +  close(file);
> \ No newline at end of file

Please fix that warning. ^^^^^


-- 
~Randy

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