Re: [PATCH 1/4] i2c: imx: check busy bit when START/STOP

Richard Zhao
2009-10-01T09:11:30Z

On Thu, Oct 1, 2009 at 4:38 PM, Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> wrote:
> On Thu, Oct 01, 2009 at 04:03:20PM +0800, Richard Zhao wrote:
>> On Thu, Oct 1, 2009 at 9:13 AM, Richard Zhao <linuxzsc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> > After START/RESTART, wait for busy bit to be set and
>> > after STOP, wait for busy bit to be clear.
>> >
>> > Signed-off-by: Richard Zhao <linuxzsc-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>> >
>> > diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
>> > index 4afba3e..156cc95 100644
>> > --- a/drivers/i2c/busses/i2c-imx.c
>> > +++ b/drivers/i2c/busses/i2c-imx.c
>> > @@ -125,14 +125,19 @@ struct imx_i2c_struct {
>> >  /** Functions for IMX I2C adapter driver ***************************************
>> >  *******************************************************************************/
>> >
>> > -static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx)
>> > +static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx, int for_busy)
>> >  {
>> >        unsigned long orig_jiffies = jiffies;
>> > +       unsigned int temp;
>> >
>> >        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>> >
>> > -       /* wait for bus not busy */
>> > -       while (readb(i2c_imx->base + IMX_I2C_I2SR) & I2SR_IBB) {
>> > +       temp = readb(i2c_imx->base + IMX_I2C_I2SR);
>> > +       while (1) {
>> > +               if (for_busy && (temp & I2SR_IBB))
>> > +                       break;
>> > +               if (!for_busy && !(temp & I2SR_IBB))
>> > +                       break;
>> >                if (signal_pending(current)) {
>> >                        dev_dbg(&i2c_imx->adapter.dev,
>> >                                "<%s> I2C Interrupted\n", __func__);
>> > @@ -144,6 +149,7 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx)
>> >                        return -EIO;
>> >                }
>> >                schedule();
>> > +               temp = readb(i2c_imx->base + IMX_I2C_I2SR);
>> >        }
>> >
>> >        return 0;
>> > @@ -179,20 +185,32 @@ static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx)
>> >        return 0;
>> >  }
>> >
>> > -static void i2c_imx_start(struct imx_i2c_struct *i2c_imx)
>> > +static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
>> >  {
>> >        unsigned int temp = 0;
>> > +       int result;
>> >
>> >        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>> >
>> >        /* Enable I2C controller */
>> > +       writeb(0, i2c_imx->base + IMX_I2C_I2SR);
>> >        writeb(I2CR_IEN, i2c_imx->base + IMX_I2C_I2CR);
>> > +
>> > +       result = i2c_imx_bus_busy(i2c_imx, 0);
>> > +       if (result)
>> > +               return result;
>> > +
>> >        /* Start I2C transaction */
>> >        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
>> >        temp |= I2CR_MSTA;
>> >        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
>> > +       result = i2c_imx_bus_busy(i2c_imx, 1);
>> > +       if (result)
>> > +               return result;
>> > +
>> >        temp |= I2CR_IIEN | I2CR_MTX | I2CR_TXAK;
>> >        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
>> > +       return result;
>> >  }
>> >
>> >  static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
>> > @@ -202,16 +220,16 @@ static void i2c_imx_stop(struct imx_i2c_struct *i2c_imx)
>> >        /* Stop I2C transaction */
>> >        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>> >        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
>> > -       temp &= ~I2CR_MSTA;
>> > +       temp &= ~(I2CR_MSTA | I2CR_MTX);
>> >        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
>> > -       /* setup chip registers to defaults */
>> > -       writeb(I2CR_IEN, i2c_imx->base + IMX_I2C_I2CR);
>> > -       writeb(0, i2c_imx->base + IMX_I2C_I2SR);
>> >        /*
>> >         * This delay caused by an i.MXL hardware bug.
>> >         * If no (or too short) delay, no "STOP" bit will be generated.
>> >         */
>> >        udelay(i2c_imx->disable_delay);
>> > +
>> > +       i2c_imx_bus_busy(i2c_imx, 0);
>> > +
>> >        /* Disable I2C controller */
>> >        writeb(0, i2c_imx->base + IMX_I2C_I2CR);
>> >  }
>> > @@ -344,7 +362,7 @@ static int i2c_imx_read(struct imx_i2c_struct *i2c_imx, struct i2c_msg *msgs)
>> >                        dev_dbg(&i2c_imx->adapter.dev,
>> >                                "<%s> clear MSTA\n", __func__);
>> >                        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
>> > -                       temp &= ~I2CR_MSTA;
>> > +                       temp &= ~(I2CR_MSTA | I2CR_MTX);
>> >                        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
>> >                } else if (i == (msgs->len - 2)) {
>> >                        dev_dbg(&i2c_imx->adapter.dev,
>> > @@ -370,14 +388,11 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
>> >
>> >        dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
>> >
>> > -       /* Check if i2c bus is not busy */
>> > -       result = i2c_imx_bus_busy(i2c_imx);
>> > +       /* Start I2C transfer */
>> > +       result = i2c_imx_start(i2c_imx);
>> >        if (result)
>> >                goto fail0;
>> >
>> > -       /* Start I2C transfer */
>> > -       i2c_imx_start(i2c_imx);
>> > -
>> >        /* read/write data */
>> >        for (i = 0; i < num; i++) {
>> >                if (i) {
>> > @@ -386,6 +401,9 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
>> >                        temp = readb(i2c_imx->base + IMX_I2C_I2CR);
>> >                        temp |= I2CR_RSTA;
>> >                        writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
>> > +                       result =  i2c_imx_bus_busy(i2c_imx, 1);
>> > +                       if (result)
>> > +                               goto fail0;
>> >                }
>> >                dev_dbg(&i2c_imx->adapter.dev,
>> >                        "<%s> transfer message: %d\n", __func__, i);
>> > --
>> > 1.6.0.4
>> >
>> >
>>
>> Hi Sascha,
>>
>> So I assume you have no comments about this patch ?
>
> No, I'm still thinking about it. The commit message says *what* you're
> doing, but not *why*. Is it a concrete bug that you fix or is it just
> because it might be a good idea to do so?
The driver doesn't work with mx51, which is a fast cpu. So I checked
the driver, and find it didn't check IBB.
> Also, we leave i2c_imx_xfer with the controller in a well defined state.
> So if we leave this function with the controller in non busy state, why
> do we have to check for non busy again when we enter it again?
I2C is a multi-master bus.
Richard
>
> Sascha
>
>
> --
> Pengutronix e.K.                           |                             |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |
>