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Date:   Thu, 10 Sep 2020 08:32:25 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
To:     Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
Cc:     Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>,
        linux-i2c@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, linux-actions@lists.infradead.org
Subject: Re: [PATCH v2 1/1] i2c: busses: Add support for atomic transfers in
 Actions Semi Owl driver
Message-ID: <20200910030225.GA10495@mani>
References: <b6c56858854805b0f03e29b7dde40b20796d5c93.1599561278.git.cristian.ciocaltea@gmail.com>
 <20200909151748.GA11397@mani>
 <20200909165915.GA387239@BV030612LT>
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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.

> > >  			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.

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