Re: [PATCH v2 1/1] i2c: busses: Add support for atomic transfers in Actions Semi Owl driver

[Cristian Ciocaltea <cristian.ciocaltea@gmail.com>]

On Thu, Sep 10, 2020 at 08:32:25AM +0530, Manivannan Sadhasivam wrote:
> On 0909, Cristian Ciocaltea wrote:
> > Hi Mani,
> > 
> > Thanks for the review!
> > 
> > On Wed, Sep 09, 2020 at 08:47:48PM +0530, Manivannan Sadhasivam wrote:
> > > Hi Cristi,
> > > 
> > > On 0908, 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.
> > > > 
> > > 
> > > Thanks for the patch! I just have couple of minor comments and other
> > > than that it looks good to me.
> > > 
> > > > Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
> > > > ---
> > > > Changes in v2:
> > > >  - Dropped unused return codes from owl_i2c_xfer_data(), per Mani's review
> > > >  - Rebased patch on v5.9-rc4
> > > > 
> > > >  drivers/i2c/busses/i2c-owl.c | 78 ++++++++++++++++++++++++++----------
> > > >  1 file changed, 57 insertions(+), 21 deletions(-)
> > > > 
> > > > diff --git a/drivers/i2c/busses/i2c-owl.c b/drivers/i2c/busses/i2c-owl.c
> > > > index 672f1f239bd6..29605257831f 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 void 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;
> > > >  	}
> > > >  
> > > >  	/* 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;
> > > >  	}
> > > >  
> > > >  	/* Handle FIFO read */
> > > > @@ -196,18 +195,28 @@ 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) {
> > > 
> > > Spurious change?
> > 
> > I have just fixed a small indentation issue (removed extra space char
> > in front of OWL_I2C...). I will revert it if you think it's not the right
> > context for doing this (located ~10 lines bellow the previous edit).
> > 
> 
> The extra space was there to align with the starting of 'readl', so please keep
> it as it is.

Right, sorry! I aligned it with the other 'readl' a few lines above and
I missed the extra offset caused by the '!' operator.

> > > >  			writel(msg->buf[i2c_dev->msg_ptr++],
> > > >  			       i2c_dev->base + OWL_I2C_REG_TXDAT);
> > > >  		}
> > > >  	}
> > > > +}
> > > > +
> > > > +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);
> > > >  
> > > > -stop:
> > > >  	/* 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 +244,8 @@ 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 +289,12 @@ 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 +362,33 @@ 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);
> > > 
> > > You are not clearing the pending interrupts here.
> > 
> > I assumed this is not needed for atomic contexts since the controller
> > interrupt is disabled (please see the comment above: Enable/disable I2C
> > controller interrupt).
> > 
> > Otherwise I will simply move the clear pending interrupts code from 
> > owl_i2c_interrupt() to owl_i2c_xfer_data().
> > 
> 
> Hmm. My intention was to say that we are not clearing the error bits when they
> happen but I misinterpreted that setting IRQP will take care of that but it
> doesn't.
> 
> So I think you should submit a patch which writes to RNB and BEB fields when
> they are set (writing 1 will clear the interrupts) and ignore my previous
> comment.

Sure, I can handle this. I assume this should be a separate patch, to
be applied before the current patch. Should I submit a patch series
instead?

Thanks,
Cristi

> Thanks,
> Mani
> 
> > > Thanks,
> > > Mani
> > > 
> > > > +
> > > >  	ret = i2c_dev->err < 0 ? i2c_dev->err : num;
> > > >  
> > > >  err_exit:
> > > > @@ -379,9 +402,22 @@ 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
> > > > 
> > 
> > Kind regards,
> > Cristi