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author | Jonathan Corbet <corbet@lwn.net> | 2016-09-06 07:15:24 -0600 |
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committer | Jonathan Corbet <corbet@lwn.net> | 2016-09-06 09:14:52 -0600 |
commit | 5e995786850e78b7950f6979a6bdd3990abc89cd (patch) | |
tree | e95ff5fb0ee816885b92206fdff70aa1bfe4a027 /Documentation/driver-api/hsi.rst | |
parent | 70fc1f547a91c137913a23a0f7a4a89c33930c6a (diff) | |
download | linux-5e995786850e78b7950f6979a6bdd3990abc89cd.tar.bz2 |
docs: split up serial-interfaces.rst
It never made sense to keep these documents together; move each into its
own file.
Drop the section numbering on hsi.txt on its way to its own file.
Suggested-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/driver-api/hsi.rst')
-rw-r--r-- | Documentation/driver-api/hsi.rst | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/Documentation/driver-api/hsi.rst b/Documentation/driver-api/hsi.rst new file mode 100644 index 000000000000..f9cec02b72a1 --- /dev/null +++ b/Documentation/driver-api/hsi.rst @@ -0,0 +1,88 @@ +High Speed Synchronous Serial Interface (HSI) +============================================= + +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 ----------->| | + | | | | + | | | | + +------------+ +---------------+ + +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. + +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 + +The kernel HSI API +------------------ + +.. kernel-doc:: include/linux/hsi/hsi.h + :internal: + +.. kernel-doc:: drivers/hsi/hsi_core.c + :export: + |