Messages in this thread | | | From | Vitor Soares <> | Subject | RE: [PATCH v3 5/5] add i3cdev documentation | Date | Wed, 19 Feb 2020 00:46:37 +0000 |
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Hi Jonathan,
From: Vitor Soares <vitor.soares@synopsys.com> Date: Wed, Feb 19, 2020 at 00:20:43
> This patch add documentation for the userspace API of i3cdev module. >
I just realize now that I missed the commit message, it should be: userspace-api: i3c: add i3cdev documentation
I will do next time.
> Signed-off-by: Vitor Soares <vitor.soares@synopsys.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 > +the i3c devices. By default, the i3cdev module only exposes the i3c devices > +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 > +<bus id>-<Provisional ID> same way they can be found in /sys/bus/i3c/devices/. > +:: > + > +# 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 > +using the Sysfs to unbind the kernel driver from the device. > + > +BASIC CHARACTER DEVICE API > +=============================== > +For now, the API has only support private SDR read and write transfers. > +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 > + 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); > + > +Now the file is opened, we can perform the operations available:: > + > + /* Write function */ > + uint_t8 buf[] = {0x00, 0xde, 0xad, 0xbe, 0xef} > + 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 > -- > 2.7.4
Best regards, Vitor Soares
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