On Wed, Feb 01, 2017 at 10:53:55AM -0600, Christopher Bostic wrote: > From: Chris Bostic <cbostic@xxxxxxxxxx> > > Add details on the basic functions of the FSI serial bus. > > Signed-off-by: Chris Bostic <cbostic@xxxxxxxxxx> > --- > Documentation/devicetree/bindings/fsi/fsi.txt | 54 +++++++++++++++++++++++++++ > 1 file changed, 54 insertions(+) > create mode 100644 Documentation/devicetree/bindings/fsi/fsi.txt > > diff --git a/Documentation/devicetree/bindings/fsi/fsi.txt b/Documentation/devicetree/bindings/fsi/fsi.txt > new file mode 100644 > index 0000000..7fa2394 > --- /dev/null > +++ b/Documentation/devicetree/bindings/fsi/fsi.txt > @@ -0,0 +1,54 @@ > +FSI: Flexible Support processor Interface > + > +FSI is a two line serial bus capable of running at speeds up to 166 MHz. > +The lines consist of a clock responsible for synchronizing the target device > +(slave) with the master which is responsible for all transactions on the bus. > +The master owns the clock line and is the only side allowed to change its > +state. The second line, SDA, is a data line that conveys information to/from > +the slave who samples based on the clock line. The data line is > +bi-directional. > + > +The master initiates communication by sending a command to the slave and > +depending on the type of command will allow the slave to control the bus > +to return requested data. All commands are CRC protected. The slave upon > +receipt of a command will determine if the CRC is correct and discard > +the data if noise has corrupted the line. In the same manner the master > +will verify the CRC received from the slave. > + > +Types of commands: > +Read 32 bit: Read a 32 bit word from a specified address on the slave. > +Read 16 bit: Read a 16 bit 'half word' from a specified address on the slave. > +read 8 bit: Read a byte from a specified address on the slave. > +Write 32,16,8 bit: Write to a specified address on the slave with the provided > + data. > +BREAK: Initialize the slave's logic to receive commands. > +TERM: Terminate the slave's error lockout to resume communications > + after an error on the bus is detected. > +D-POLL: Poll the slave to determine when it is no longer buy processing > + a previous command. > +I-POLL: Interrupt signal check. Master queries slave to see if any > + interrupts are asserting. > + > +High fanout capability: > +FSI buses can be chained together in 'hub' configurations to expand the > +available communications channels and thus allow connetion to more slaves. > + > + > +Typical implementation > + > + FSI master ----- slave with local FSI master (hub) ------- downstream slave > + > + > +Each two line combination of a clock and data line is collectively referred > +to as a 'FSI link'. Depending on hardware the primary FSI master may support > +up to 64 links. Hub FSI masters can support at most 8 links. Total number > +of supported slaves can grow exponentially depending on how many hubs are > +placed in the path. Presently only two hubs in the chain are allowed but > +in the future this may be expanded. This document now isn't really more that a description of FSI. You need to define how the above bus structure gets reflected in DT. I assume the root is the FSI master, each child node is a link, a child can be a hub with its children being more links. What is the format of reg property is another thing to define. > + > +The slave hardware logic responsible for decoding FSI master commands is > +contained in a CFAM (Common Field replaceable unit Access Macro). Up to > +4 slaves or CFAMs can be connected on each FSI link. CFAMs in addition > +to the slave logic (or engine) can contain other functions that allow access > +via FSI. Common additional functionality includes I2C masters, GPIO > +controllers, UARTs, etc... > -- > 1.8.2.2 > -- 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
