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

Richard Zhao
2009-10-01T14:54:46Z

On Thu, Oct 1, 2009 at 5:52 PM, Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> wrote:
> On Thu, Oct 01, 2009 at 05:11:30PM +0800, Richard Zhao wrote:
>> 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.
>
> Ah, so 'make the driver work on i.MX51' is a good statement which should
> be part of the commit message.
Well, maybe I can mention it.
But I think the good point is to present what you modified, not the side effect.
>
>> > 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.
>
> So you say with this patch the driver becomes multi master capable? If
> so, it should also be part of the commit message.
Yes. But I don't have multi-master system. So I can't say that.
The code is just taken from Freescale latest code. Without it, It
could also cause a device error. I forget the details. Anyway, it
doesn't make anything wrong.

Thanks
Richard
>
> Sascha
>
>
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