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    SubjectRe: [2/5] i2c: davinci: query STP always when NACK is received
    Hello,

    On Thu, Nov 20, 2014 at 12:03:05PM +0200, Grygorii Strashko wrote:
    > According to I2C specification the NACK should be handled as folowing:
    s/folowing/follows/

    > "When SDA remains HIGH during this ninth clock pulse, this is defined as the Not
    > Acknowledge signal. The master can then gene rate either a STOP condition to
    s/gene rate/generate/

    > abort the transfer, or a repeated START condition to start a new transfer."
    > [http://www.nxp.com/documents/user_manual/UM10204.pdf]
    The link is nice, but pointing out that this is the i2c spec would be
    nice.

    > The same is recomened by TI I2C wiki:
    s/recomened/recommended/

    > http://processors.wiki.ti.com/index.php/I2C_Tips
    If the specification tells what to do, there is no need to further
    support your claim.

    > Currently, the Davinci I2C driver interrupts I2C trunsfer in case of NACK, but
    s/trunsfer/transfer/

    > It queries Stop condition DAVINCI_I2C_MDR_REG.STP=1 only if NACK has been received
    s/It/it/

    > during the last message transmitting/recieving.
    s/transmitting/transmitted/; s/recieving/received/

    I think I don't understand this sentence even with the typos corrected.
    Do you want to say:

    Currently the Davinci i2c driver interrupts the transfer on receipt of a
    NACK but fails to send a STOP in some situations and so makes the bus
    stuck.

    > This may lead to Bus stuck in "Bus Busy" until I2C IP reset (idle/enable) if
    > during SMBus reading transaction the first I2C message is NACKed.
    Did you hit this problem, or is this a theoretical issue?

    Assuming this is a candidate for stable, adding a Fixes:-footer would be
    nice.

    > Hence, fix it by querying Stop condition (STP) always when NACK is received.
    >
    > This patch fixes Davinci I2C in the same way it was done for OMAP I2C
    > commit cda2109a26eb ("i2c: omap: query STP always when NACK is received").
    >
    > More info can be found at:
    > https://lkml.org/lkml/2013/7/16/159
    > http://patchwork.ozlabs.org/patch/249790/
    I'd drop this "more info" paragraph.

    > CC: Sekhar Nori <nsekhar@ti.com>
    > CC: Kevin Hilman <khilman@deeprootsystems.com>
    > CC: Santosh Shilimkar <ssantosh@kernel.org>
    > CC: Murali Karicheri <m-karicheri2@ti.com>
    > Reported-by: Hein Tibosch <hein_tibosch@yahoo.es>
    Is this Reported-by tag reused from the omap issue?

    > Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
    > ---
    > drivers/i2c/busses/i2c-davinci.c | 8 +++-----
    > 1 file changed, 3 insertions(+), 5 deletions(-)
    >
    > diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
    > index 9bbfb8f..2cef115 100644
    > --- a/drivers/i2c/busses/i2c-davinci.c
    > +++ b/drivers/i2c/busses/i2c-davinci.c
    > @@ -411,11 +411,9 @@ i2c_davinci_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg, int stop)
    > if (dev->cmd_err & DAVINCI_I2C_STR_NACK) {
    > if (msg->flags & I2C_M_IGNORE_NAK)
    > return msg->len;
    > - if (stop) {
    > - w = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
    > - w |= DAVINCI_I2C_MDR_STP;
    > - davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, w);
    > - }
    > + w = davinci_i2c_read_reg(dev, DAVINCI_I2C_MDR_REG);
    > + w |= DAVINCI_I2C_MDR_STP;
    > + davinci_i2c_write_reg(dev, DAVINCI_I2C_MDR_REG, w);
    I think this is a good change, but I wonder if the handling of
    I2C_M_IGNORE_NAK is correct here. If the controller reports a NACK say
    for the 2nd byte of a 5-byte-message, the transfer supposed to
    continue, right? (Hmm, maybe the framework handle this and restarts the
    transfer with I2C_M_NOSTART but the davinci driver doesn't seem to
    handle this flag?)

    Best regards
    Uwe

    > return -EREMOTEIO;
    > }
    > return -EIO;

    --
    Pengutronix e.K. | Uwe Kleine-König |
    Industrial Linux Solutions | http://www.pengutronix.de/ |


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