Add a document, which gives a rough introduction about what HSI is and how its handled by the Linux kernel. Signed-off-by: Sebastian Reichel <sre@xxxxxxxxxx> --- Documentation/hsi.txt | 75 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 75 insertions(+) create mode 100644 Documentation/hsi.txt diff --git a/Documentation/hsi.txt b/Documentation/hsi.txt new file mode 100644 index 0000000..6ac6cd5 --- /dev/null +++ b/Documentation/hsi.txt @@ -0,0 +1,75 @@ +HSI - High-speed Synchronous Serial Interface + +1. Introduction +~~~~~~~~~~~~~~~ + +High Speed Syncronous Interface (HSI) is a fullduplex, low latency protocol, +that is optimized for die-level interconnect between an Application Processor +and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and +implemented by multiple vendors since then. + +The HSI interface supports full duplex communication over multiple channels +(typically 8) and is capable of reaching speeds up to 200 Mbit/s. + +The serial protocol uses two signals, DATA and FLAG as combined data and clock +signals and an additional READY signal for flow control. An additional WAKE +signal can be used to wakeup the chips from standby modes. The signals are +commonly prefixed by AC for signals going from the application die to the +cellular die and CA for signals going the other way around. + ++------------+ +---------------+ +| Cellular | | Application | +| Die | | Die | +| | - - - - - - CAWAKE - - - - - - >| | +| T|------------ CADATA ------------>|R | +| X|------------ CAFLAG ------------>|X | +| |<----------- ACREADY ------------| | +| | | | +| | | | +| |< - - - - - ACWAKE - - - - - - -| | +| R|<----------- ACDATA -------------|T | +| X|<----------- ACFLAG -------------|X | +| |------------ CAREADY ----------->| | +| | | | +| | | | ++------------+ +---------------+ + +2. HSI Subsystem in Linux +~~~~~~~~~~~~~~~~~~~~~~~~~ + +In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. +The hsi subsystem contains drivers for hsi controllers including support for +multi-port controllers and provides a generic API for using the HSI ports. + +It also contains HSI client drivers, which make use of the generic API to +implement a protocol used on the HSI interface. These client drivers can +use an arbitrary number of channels. + +3. hsi-char Device +~~~~~~~~~~~~~~~~~~ + +Each port automatically registers a generic client driver called hsi_char, +which provides a charecter device for userspace representing the HSI port. +It can be used to communicate via HSI from userspace. Userspace may +configure the hsi_char device using the following ioctl commands: + +* HSC_RESET: + - flush the HSI port + +* HSC_SET_PM + - enable or disable the client. + +* HSC_SEND_BREAK + - send break + +* HSC_SET_RX + - set RX configuration + +* HSC_GET_RX + - get RX configuration + +* HSC_SET_TX + - set TX configuration + +* HSC_GET_TX + - get TX configuration -- 1.9.0 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
