• Federico Vaga's avatar
    i2c: ocores: stop transfer on timeout · e7663ef5
    Federico Vaga authored
    Detecting a timeout is ok, but we also need to assert a STOP command on
    the bus in order to prevent it from generating interrupts when there are
    no on going transfers.
    Example: very long transmission.
    1. ocores_xfer: START a transfer
    2. ocores_isr : handle byte by byte the transfer
    3. ocores_xfer: goes in timeout [[bugfix here]]
    4. ocores_xfer: return to I2C subsystem and to the I2C driver
    5. I2C driver : it may clean up the i2c_msg memory
    6. ocores_isr : receives another interrupt (pending bytes to be
                    transferred) but the i2c_msg memory is invalid now
    So, since the transfer was too long, we have to detect the timeout and
    STOP the transfer.
    Another point is that we have a critical region here. When handling the
    timeout condition we may have a running IRQ handler. For this reason I
    introduce a spinlock.
    In order to make easier to understan locking I have:
    - added a new function to handle timeout
    - modified the current ocores_process() function in order to be protected
      by the new spinlock
    Like this it is obvious at first sight that this locking serializes
    the execution of ocores_process() and ocores_process_timeout()
    Signed-off-by: default avatarFederico Vaga <federico.vaga@cern.ch>
    Reviewed-by: default avatarAndrew Lunn <andrew@lunn.ch>
    Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>