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    SubjectRe: [PATCH 2/4] i2c-designware: always set the STOP bit after last byte
    Hi,

    On Thu, Jan 17, 2013 at 12:31:05PM +0200, Mika Westerberg wrote:
    > If IC_EMPTYFIFO_HOLD_MASTER_EN is set to one, the DesignWare I2C controller
    > doesn't generate STOP on the bus when the FIFO is empty. This violates the
    > rules of Linux I2C stack as it requires that the STOP is issued once the
    > i2c_transfer() is finished.
    >
    > However, there is no way to detect this from the hardware registers, so we
    > must make sure that the STOP bit is always set once the last byte of the
    > last message is transferred.
    >
    > This patch is based on the work of Dirk Brandewie.
    >
    > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    > ---
    > drivers/i2c/busses/i2c-designware-core.c | 16 ++++++++++++++--
    > 1 file changed, 14 insertions(+), 2 deletions(-)
    >
    > diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
    > index f5258c2..94fd818 100644
    > --- a/drivers/i2c/busses/i2c-designware-core.c
    > +++ b/drivers/i2c/busses/i2c-designware-core.c
    > @@ -413,11 +413,23 @@ i2c_dw_xfer_msg(struct dw_i2c_dev *dev)
    > rx_limit = dev->rx_fifo_depth - dw_readl(dev, DW_IC_RXFLR);
    >
    > while (buf_len > 0 && tx_limit > 0 && rx_limit > 0) {
    > + u32 cmd = 0;
    > +
    > + /*
    > + * If IC_EMPTYFIFO_HOLD_MASTER_EN is set we must
    > + * manually set the stop bit. However, it cannot be
    > + * detected from the registers so we set it always
    > + * when writing/reading the last byte.
    > + */
    > + if (dev->msg_write_idx == dev->msgs_num - 1 &&
    > + buf_len == 1)
    > + cmd |= BIT(9);
    > +
    > if (msgs[dev->msg_write_idx].flags & I2C_M_RD) {
    > - dw_writel(dev, 0x100, DW_IC_DATA_CMD);
    > + dw_writel(dev, cmd | 0x100, DW_IC_DATA_CMD);
    > rx_limit--;
    > } else
    > - dw_writel(dev, *buf++, DW_IC_DATA_CMD);
    > + dw_writel(dev, cmd | *buf++, DW_IC_DATA_CMD);

    also need to send STP bit if I2C_M_STOP is set.

    --
    balbi
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