Re: [PATCH 1/1] i2c: busses: Add support for atomic transfers in Actions Semi Owl driver

[Cristian Ciocaltea]

Hi Mani,

Thanks for the review!

On Fri, Aug 28, 2020 at 06:34:04PM +0530, Manivannan Sadhasivam wrote:
> On 0803, Cristian Ciocaltea wrote:
> > Atomic transfers are required to properly power off a machine through
> > an I2C controlled PMIC, such as the Actions Semi ATC260x series.
> > 
> > System shutdown may happen with interrupts being disabled and, as a
> > consequence, the kernel may hang if the driver does not support atomic
> > transfers.
> > 
> > This functionality is essentially implemented by polling the FIFO
> > Status register until either Command Execute Completed or NACK Error
> > bits are set.
> > 
> > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@xxxxxxxxx>
> > ---
> >  drivers/i2c/busses/i2c-owl.c | 80 ++++++++++++++++++++++++++----------
> >  1 file changed, 59 insertions(+), 21 deletions(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-owl.c b/drivers/i2c/busses/i2c-owl.c
> > index 672f1f239bd6..90dd2e814313 100644
> > --- a/drivers/i2c/busses/i2c-owl.c
> > +++ b/drivers/i2c/busses/i2c-owl.c
> > @@ -14,6 +14,7 @@
> >  #include <linux/i2c.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/io.h>
> > +#include <linux/iopoll.h>
> >  #include <linux/module.h>
> >  #include <linux/of_device.h>
> >  
> > @@ -76,6 +77,7 @@
> >  #define OWL_I2C_FIFOCTL_TFR	BIT(2)
> >  
> >  /* I2Cc_FIFOSTAT Bit Mask */
> > +#define OWL_I2C_FIFOSTAT_CECB	BIT(0)
> >  #define OWL_I2C_FIFOSTAT_RNB	BIT(1)
> >  #define OWL_I2C_FIFOSTAT_RFE	BIT(2)
> >  #define OWL_I2C_FIFOSTAT_TFF	BIT(5)
> > @@ -83,7 +85,8 @@
> >  #define OWL_I2C_FIFOSTAT_RFD	GENMASK(15, 8)
> >  
> >  /* I2C bus timeout */
> > -#define OWL_I2C_TIMEOUT		msecs_to_jiffies(4 * 1000)
> > +#define OWL_I2C_TIMEOUT_MS	(4 * 1000)
> > +#define OWL_I2C_TIMEOUT		msecs_to_jiffies(OWL_I2C_TIMEOUT_MS)
> >  
> >  #define OWL_I2C_MAX_RETRIES	50
> >  
> > @@ -161,29 +164,25 @@ static void owl_i2c_set_freq(struct owl_i2c_dev *i2c_dev)
> >  	writel(OWL_I2C_DIV_FACTOR(val), i2c_dev->base + OWL_I2C_REG_CLKDIV);
> >  }
> >  
> > -static irqreturn_t owl_i2c_interrupt(int irq, void *_dev)
> > +static int owl_i2c_xfer_data(struct owl_i2c_dev *i2c_dev)
> >  {
> > -	struct owl_i2c_dev *i2c_dev = _dev;
> >  	struct i2c_msg *msg = i2c_dev->msg;
> > -	unsigned long flags;
> >  	unsigned int stat, fifostat;
> >  
> > -	spin_lock_irqsave(&i2c_dev->lock, flags);
> > -
> >  	i2c_dev->err = 0;
> >  
> >  	/* Handle NACK from slave */
> >  	fifostat = readl(i2c_dev->base + OWL_I2C_REG_FIFOSTAT);
> >  	if (fifostat & OWL_I2C_FIFOSTAT_RNB) {
> >  		i2c_dev->err = -ENXIO;
> > -		goto stop;
> > +		return 1;
> 
> This looks odd! And moreover you're not making use of this return value
> anywhere.

You are right, that's just a leftover from my initial implementation
and I totally missed it when I did the final cleanup. Thanks for
spotting it!

> Thanks,
> Mani

If there is nothing else, I can submit the revised patch.

Regards,
Cristi

> >  	}
> >  
> >  	/* Handle bus error */
> >  	stat = readl(i2c_dev->base + OWL_I2C_REG_STAT);
> >  	if (stat & OWL_I2C_STAT_BEB) {
> >  		i2c_dev->err = -EIO;
> > -		goto stop;
> > +		return 1;
> >  	}
> >  
> >  	/* Handle FIFO read */
> > @@ -196,18 +195,30 @@ static irqreturn_t owl_i2c_interrupt(int irq, void *_dev)
> >  	} else {
> >  		/* Handle the remaining bytes which were not sent */
> >  		while (!(readl(i2c_dev->base + OWL_I2C_REG_FIFOSTAT) &
> > -			 OWL_I2C_FIFOSTAT_TFF) && i2c_dev->msg_ptr < msg->len) {
> > +			OWL_I2C_FIFOSTAT_TFF) && i2c_dev->msg_ptr < msg->len) {
> >  			writel(msg->buf[i2c_dev->msg_ptr++],
> >  			       i2c_dev->base + OWL_I2C_REG_TXDAT);
> >  		}
> >  	}
> >  
> > -stop:
> > +	return 0;
> > +}
> > +
> > +static irqreturn_t owl_i2c_interrupt(int irq, void *_dev)
> > +{
> > +	struct owl_i2c_dev *i2c_dev = _dev;
> > +	unsigned long flags;
> > +
> > +	spin_lock_irqsave(&i2c_dev->lock, flags);
> > +
> > +	owl_i2c_xfer_data(i2c_dev);
> > +
> >  	/* Clear pending interrupts */
> >  	owl_i2c_update_reg(i2c_dev->base + OWL_I2C_REG_STAT,
> >  			   OWL_I2C_STAT_IRQP, true);
> >  
> >  	complete_all(&i2c_dev->msg_complete);
> > +
> >  	spin_unlock_irqrestore(&i2c_dev->lock, flags);
> >  
> >  	return IRQ_HANDLED;
> > @@ -235,8 +246,8 @@ static int owl_i2c_check_bus_busy(struct i2c_adapter *adap)
> >  	return 0;
> >  }
> >  
> > -static int owl_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> > -			       int num)
> > +static int owl_i2c_xfer_common(struct i2c_adapter *adap, struct i2c_msg *msgs,
> > +			       int num, bool atomic)
> >  {
> >  	struct owl_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
> >  	struct i2c_msg *msg;
> > @@ -280,11 +291,12 @@ static int owl_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> >  		goto err_exit;
> >  	}
> >  
> > -	reinit_completion(&i2c_dev->msg_complete);
> > +	if (!atomic)
> > +		reinit_completion(&i2c_dev->msg_complete);
> >  
> > -	/* Enable I2C controller interrupt */
> > +	/* Enable/disable I2C controller interrupt */
> >  	owl_i2c_update_reg(i2c_dev->base + OWL_I2C_REG_CTL,
> > -			   OWL_I2C_CTL_IRQE, true);
> > +			   OWL_I2C_CTL_IRQE, !atomic);
> >  
> >  	/*
> >  	 * Select: FIFO enable, Master mode, Stop enable, Data count enable,
> > @@ -352,20 +364,33 @@ static int owl_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> >  
> >  	spin_unlock_irqrestore(&i2c_dev->lock, flags);
> >  
> > -	time_left = wait_for_completion_timeout(&i2c_dev->msg_complete,
> > -						adap->timeout);
> > +	if (atomic) {
> > +		/* Wait for Command Execute Completed or NACK Error bits */
> > +		ret = readl_poll_timeout_atomic(i2c_dev->base + OWL_I2C_REG_FIFOSTAT,
> > +						val, val & (OWL_I2C_FIFOSTAT_CECB |
> > +							    OWL_I2C_FIFOSTAT_RNB),
> > +						10, OWL_I2C_TIMEOUT_MS * 1000);
> > +	} else {
> > +		time_left = wait_for_completion_timeout(&i2c_dev->msg_complete,
> > +							adap->timeout);
> > +		if (!time_left)
> > +			ret = -ETIMEDOUT;
> > +	}
> >  
> >  	spin_lock_irqsave(&i2c_dev->lock, flags);
> > -	if (time_left == 0) {
> > +
> > +	if (ret) {
> >  		dev_err(&adap->dev, "Transaction timed out\n");
> >  		/* Send stop condition and release the bus */
> >  		owl_i2c_update_reg(i2c_dev->base + OWL_I2C_REG_CTL,
> >  				   OWL_I2C_CTL_GBCC_STOP | OWL_I2C_CTL_RB,
> >  				   true);
> > -		ret = -ETIMEDOUT;
> >  		goto err_exit;
> >  	}
> >  
> > +	if (atomic)
> > +		owl_i2c_xfer_data(i2c_dev);
> > +
> >  	ret = i2c_dev->err < 0 ? i2c_dev->err : num;
> >  
> >  err_exit:
> > @@ -379,9 +404,22 @@ static int owl_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> >  	return ret;
> >  }
> >  
> > +static int owl_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
> > +			int num)
> > +{
> > +	return owl_i2c_xfer_common(adap, msgs, num, false);
> > +}
> > +
> > +static int owl_i2c_xfer_atomic(struct i2c_adapter *adap,
> > +			       struct i2c_msg *msgs, int num)
> > +{
> > +	return owl_i2c_xfer_common(adap, msgs, num, true);
> > +}
> > +
> >  static const struct i2c_algorithm owl_i2c_algorithm = {
> > -	.master_xfer    = owl_i2c_master_xfer,
> > -	.functionality  = owl_i2c_func,
> > +	.master_xfer	     = owl_i2c_xfer,
> > +	.master_xfer_atomic  = owl_i2c_xfer_atomic,
> > +	.functionality	     = owl_i2c_func,
> >  };
> >  
> >  static const struct i2c_adapter_quirks owl_i2c_quirks = {
> > -- 
> > 2.28.0
> >