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

Sascha Hauer s.hauer at pengutronix.de
Tue Sep 29 10:06:12 EDT 2009


On Tue, Sep 29, 2009 at 09:54:05PM +0800, Richard Zhao wrote:
> Thanks, Sacha. See comments inline.
> 
> On Tue, Sep 29, 2009 at 9:25 PM, Sascha Hauer <s.hauer at pengutronix.de> wrote:
> > Hi Richard,
> >
> >
> > On Tue, Sep 29, 2009 at 07:41:44PM +0800, Richard Zhao wrote:
> >> After START, wait busy bit to be set and
> >> after STOP, wait busy bit to be clear.
> >>
> >> Disable clock when it's possible to save power.
> >>
> >> Signed-off-by: Richard Zhao <linuxzsc at gmail.com>
> >> ---
> >>  drivers/i2c/busses/i2c-imx.c |  116 ++++++++++++++++++++++++++++++++----------
> >>  1 files changed, 88 insertions(+), 28 deletions(-)
> >>
> >> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> >> index 4afba3e..59cde70 100644
> >> --- a/drivers/i2c/busses/i2c-imx.c
> >> +++ b/drivers/i2c/busses/i2c-imx.c
> >> @@ -120,19 +120,40 @@ struct imx_i2c_struct {
> >>       wait_queue_head_t       queue;
> >>       unsigned long           i2csr;
> >>       unsigned int            disable_delay;
> >> +     unsigned int            ifdr; /* IMX_I2C_IFDR */
> >>  };
> >>
> >>  /** Functions for IMX I2C adapter driver
> >> ***************************************
> >>  *******************************************************************************/
> >>
> >> -static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx)
> >> +#ifdef CONFIG_I2C_DEBUG_BUS
> >> +#define reg_dump(i2c_imx) \
> >> +{ \
> >> +     printk(KERN_DEBUG "fun %s:%d ", __func__, __LINE__); \
> >> +     printk(KERN_DEBUG "IADR %02x IFDR %02x I2CR %02x I2SR %02x\n", \
> >> +             readb(i2c_imx->base + IMX_I2C_IADR), \
> >> +             readb(i2c_imx->base + IMX_I2C_IFDR), \
> >> +             readb(i2c_imx->base + IMX_I2C_I2CR), \
> >> +             readb(i2c_imx->base + IMX_I2C_I2SR)); \
> >> +}
> >> +#else
> >> +#define reg_dump(i2c_imx)
> >> +#endif
> >> +
> >
> > Can you please remove this reg_dump? If we really need this it should be
> > in an extra patch and not clutter this one.
> I think it's needed. It helps much to debug and don't effect
> performance by default.
> >
> >> +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 */
> >
> > This comment seems wrong now. This function waits for busy or not busy
> > depending on for_busy.
> Right. Thanks
> >
> >> -     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__);
> >> @@ -141,9 +162,11 @@ static int i2c_imx_bus_busy(struct imx_i2c_struct *i2c_imx)
> >>               if (time_after(jiffies, orig_jiffies + HZ / 1000)) {
> >>                       dev_dbg(&i2c_imx->adapter.dev,
> >>                               "<%s> I2C bus is busy\n", __func__);
> >> +                     reg_dump(i2c_imx);
> >>                       return -EIO;
> >>               }
> >>               schedule();
> >> +             temp = readb(i2c_imx->base + IMX_I2C_I2SR);
> >>       }
> >>
> >>       return 0;
> >> @@ -158,9 +181,11 @@ static int i2c_imx_trx_complete(struct
> >> imx_i2c_struct *i2c_imx)
> >>
> >>       if (unlikely(result < 0)) {
> >>               dev_dbg(&i2c_imx->adapter.dev, "<%s> result < 0\n", __func__);
> >> +             reg_dump(i2c_imx);
> >>               return result;
> >>       } else if (unlikely(!(i2c_imx->i2csr & I2SR_IIF))) {
> >>               dev_dbg(&i2c_imx->adapter.dev, "<%s> Timeout\n", __func__);
> >> +             reg_dump(i2c_imx);
> >>               return -ETIMEDOUT;
> >>       }
> >>       dev_dbg(&i2c_imx->adapter.dev, "<%s> TRX complete\n", __func__);
> >> @@ -172,6 +197,7 @@ static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx)
> >>  {
> >>       if (readb(i2c_imx->base + IMX_I2C_I2SR) & I2SR_RXAK) {
> >>               dev_dbg(&i2c_imx->adapter.dev, "<%s> No ACK\n", __func__);
> >> +             reg_dump(i2c_imx);
> >>               return -EIO;  /* No ACK */
> >>       }
> >>
> >> @@ -179,20 +205,37 @@ 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__);
> >>
> >> +     clk_enable(i2c_imx->clk);
> >> +     writeb(i2c_imx->ifdr, i2c_imx->base + IMX_I2C_IFDR);
> >>       /* 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) {
> >> +             reg_dump(i2c_imx);
> >> +             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) {
> >> +             reg_dump(i2c_imx);
> >> +             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)
> >> @@ -202,18 +245,21 @@ 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);
> >
> > This change seems unrelated. Is it necessary?
> Yes. It's about STOP. It's better clear MTX. We must generate STOP
> before read the last byte of Data register. If not, there will be an
> extra 9bit clock.
> >
> >>       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);
> >> +
> >> +
> >
> > double blank line
> Right.
> >
> >> +     if (i2c_imx_bus_busy(i2c_imx, 0))
> >> +             reg_dump(i2c_imx);
> >> +
> >>       /* Disable I2C controller */
> >>       writeb(0, i2c_imx->base + IMX_I2C_I2CR);
> >> +     clk_disable(i2c_imx->clk);
> >>  }
> >>
> >>  static void __init i2c_imx_set_clk(struct imx_i2c_struct *i2c_imx,
> >> @@ -233,17 +279,19 @@ static void __init i2c_imx_set_clk(struct
> >> imx_i2c_struct *i2c_imx,
> >>       else
> >>               for (i = 0; i2c_clk_div[i][0] < div; i++);
> >>
> >> -     /* Write divider value to register */
> >> -     writeb(i2c_clk_div[i][1], i2c_imx->base + IMX_I2C_IFDR);
> >
> > Why can't we write this value directly anymore...
> clock will be enable/disable in start/stop
> >
> >> -
> >> -     /*
> >> -      * There dummy delay is calculated.
> >> -      * It should be about one I2C clock period long.
> >> -      * This delay is used in I2C bus disable function
> >> -      * to fix chip hardware bug.
> >> -      */
> >> -     i2c_imx->disable_delay = (500000U * i2c_clk_div[i][0]
> >> -             + (i2c_clk_rate / 2) - 1) / (i2c_clk_rate / 2);
> >> +     /* Store divider value */
> >> +     i2c_imx->ifdr = i2c_clk_div[i][1];
> >
> > ...but have to store it in a variable instead?
> To save power, because i2c is not aways be accessed, and it's very low
> speed bus.
> >
> >> +
> >> +     if (cpu_is_mx1()) {
> >> +             /*
> >> +              * There dummy delay is calculated.
> >> +              * It should be about one I2C clock period long.
> >> +              * This delay is used in I2C bus disable function
> >> +              * to fix chip hardware bug.
> >> +              */
> >> +             i2c_imx->disable_delay = (500000U * i2c_clk_div[i][0]
> >> +                     + (i2c_clk_rate / 2) - 1) / (i2c_clk_rate / 2);
> >> +     }
> >>
> >>       /* dev_dbg() can't be used, because adapter is not yet registered */
> >>  #ifdef CONFIG_I2C_DEBUG_BUS
> >> @@ -344,7 +392,7 @@ 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,
> >> @@ -369,14 +417,24 @@ static int i2c_imx_xfer(struct i2c_adapter *adapter,
> >>       struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
> >>
> >>       dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
> >> -
> >> +#ifdef CONFIG_I2C_DEBUG_BUS
> >> +     for (i = 0; i < num; i++) {
> >> +             printk(KERN_DEBUG "msg%d addr %02x RD %d cnt %d d:", i,
> >> +                     msgs[i].addr, msgs[i].flags & I2C_M_RD, msgs[i].len);
> >> +             if (!(msgs[i].flags & I2C_M_RD)) {
> >> +                     int j;
> >> +                     for (j = 0; j < msgs[i].len; j++)
> >> +                             printk("%02x ", msgs[i].buf[j]);
> >> +             }
> >> +             printk("\n");
> >> +     }
> >> +#endif
> >>       /* Check if i2c bus is not busy */
> >> -     result = i2c_imx_bus_busy(i2c_imx);
> >> -     if (result)
> >> -             goto fail0;
> >
> > When removing the code you should also remove the comment.
> Right
> >
> >>
> >>       /* Start I2C transfer */
> >> -     i2c_imx_start(i2c_imx);
> >> +     result = i2c_imx_start(i2c_imx);
> >> +     if (result)
> >> +             goto fail0;
> >>
> >>       /* read/write data */
> >>       for (i = 0; i < num; i++) {
> >> @@ -386,6 +444,11 @@ 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) {
> >> +                             reg_dump(i2c_imx);
> >> +                             goto fail0;
> >> +                     }
> >>               }
> >>               dev_dbg(&i2c_imx->adapter.dev,
> >>                       "<%s> transfer message: %d\n", __func__, i);
> >> @@ -442,7 +505,7 @@ static int __init i2c_imx_probe(struct
> >> platform_device *pdev)
> >>       int irq;
> >>       int ret;
> >>
> >> -     dev_dbg(&pdev->dev, "<%s>\n", __func__);
> >> +     dev_info(&pdev->dev, "<%s>\n", __func__);
> >
> > no
> Why? I even don't know how many i2c controllers we have, if I didn't
> get sysfs working. And it only print once.
> >
> >>
> >>       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> >>       if (!res) {
> >> @@ -500,7 +563,6 @@ static int __init i2c_imx_probe(struct
> >> platform_device *pdev)
> >>               dev_err(&pdev->dev, "can't get I2C clock\n");
> >>               goto fail3;
> >>       }
> >> -     clk_enable(i2c_imx->clk);
> >
> > I think it's generally a good idea to start/stop the clocks when needed
> > as you do here. It should be an extra patch though.
> You think I should split the patch to three: IBB, reg_dump, clk dis/en ?
> The idea is good, more easy to revert. but sometimes, I think it make
> small things too complex.
> Anyway, I'll follow your suggestion.

In case of regressions everybody will thank you for doing it.

Sascha


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