• Benjamin Herrenschmidt's avatar
    fsi/sbefifo: Add driver for the SBE FIFO · 9f4a8a2d
    Benjamin Herrenschmidt authored
    This driver provides an in-kernel and a user API for accessing
    the command FIFO of the SBE (Self Boot Engine) of the POWER9
    processor, via the FSI bus.
    It provides an in-kernel interface to submit command and receive
    responses, along with a helper to locate and analyse the response
    status block. It's a simple synchronous submit() type API.
    The user interface uses the write/read interface that an earlier
    version of this driver already provided, however it has some
    specific limitations in order to keep the driver simple and
    avoid using up a lot of kernel memory:
     - The user should perform a single write() with the command and
       a single read() to get the response (with a buffer big enough
       to hold the entire response).
     - On a write() the command is simply "stored" into a kernel buffer,
       it is submitted as one operation on the subsequent read(). This
       allows to have the code write directly from the FIFO into the user
       buffer and avoid hogging the SBE between the write() and read()
       syscall as it's critical that the SBE be freed asap to respond
       to the host. An extra write() will simply replace the previously
       written command.
     - A write of a single 4 bytes containing the value 0x52534554
       in big endian will trigger a reset request. No read is necessary,
       the write() call will return when the reset has been acknowledged
       or times out.
     - The command is limited to 4K bytes.
    Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
    Tested-by: Joel Stanley's avatarJoel Stanley <joel@jms.id.au>
fsi-sbefifo.h 1 KB