• Federico Vaga's avatar
    i2c: ocores: add polling interface · 69c8c0c0
    Federico Vaga authored
    This driver assumes that an interrupt line is always available for
    the I2C master. This is not always the case and this patch adds support
    for a polling version.
    Report from Andrew Lunn:
      I did some timing tests for this. On my box, we request a udelay of
      80uS. The kernel actually delays for about 79uS. We then spin in
      ocores_wait() for an additional 10-11uS, which is 3 to 4 iterations.
      There are actually 9 bits on the wire, not 8, since there is an
      ACK/NACK bit after the actual data transfer. So i changed the delay to
      (9 * 1000) / i2c->bus_clock_khz. That resulted in ocores_wait() mostly
      not looping at all. But for reading an 4K AT24 EEPROM, it increased
      the read time by 10ms, from 424ms to 434ms. So we should probably keep
      with 8.
    Signed-off-by: default avatarFederico Vaga <federico.vaga@cern.ch>
    Tested-by: default avatarAndrew Lunn <andrew@lunn.ch>
    Signed-off-by: default avatarWolfram Sang <wsa@the-dreams.de>