RE: [PATCH v6] OMAP2/3: I2C: Errata ID i207: Clear wrong RDR interrupt

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> -----Original Message-----
> From: Menon, Nishanth 
> Sent: Wednesday, April 28, 2010 3:35 PM
> To: G, Manjunath Kondaiah
> Cc: linux-omap@xxxxxxxxxxxxxxx; linux-i2c@xxxxxxxxxxxxxxx; 
> ben-linux@xxxxxxxxx; Kalliguddi, Hema; Aaro Koskinen; Tony Lindgren
> Subject: Re: [PATCH v6] OMAP2/3: I2C: Errata ID i207: Clear 
> wrong RDR interrupt
> 
> very minor comments below:
> On 04/28/2010 12:47 AM, G, Manjunath Kondaiah wrote:
> > Under certain rare conditions, I2C_STAT[13].RDR bit may be set
> > and the corresponding interrupt fire, even there is no data in
> > the receive FIFO, or the I2C data transfer is still ongoing.
> > These spurious RDR events must be ignored by the software.
> >
> > This patch handles and ignores RDR spurious interrupts.
> >
> > The below sequence is required in interrupt handler for
> > handling this errata:
> > 1. If RDR is set to 1, clear RDR
> > 2. Read I2C status register and check for BusBusy bit. If BusBusy
> > bit is set, skip remaining steps.
> > 3. If BusBusy bit is not set, perform read operation on I2C status
> > register.
> > 4. If RDR is set, clear the same. Check RDR again and clear 
> if it sets
> > RDR bit again.
> > 5. Perform I2C Data Read operation N number of times(where 
> N is value
> > read from the register BUFSTAT-RXSTAT bit fields).
> >
> > Note : This errata is applicable for OMAP2 and OMAP3 platforms only.
> > It is not applicable for OMAP4.
> >
> > Signed-off-by: Manjunatha GK<manjugk@xxxxxx>
> > Cc: linux-i2c@xxxxxxxxxxxxxxx
> > Cc: ben-linux@xxxxxxxxx
> > Cc: Kalliguddi, Hema<hemahk@xxxxxx>
> > Cc: Nishanth Menon<nm@xxxxxx>
> > Cc: Aaro Koskinen<Aaro.Koskinen@xxxxxxxxx>
> > Cc: Tony Lindgren<tony@xxxxxxxxxxx>
> > ---
> >   drivers/i2c/busses/i2c-omap.c |   40 
> ++++++++++++++++++++++++++++++++++++++++
> >   1 files changed, 40 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/i2c/busses/i2c-omap.c 
> b/drivers/i2c/busses/i2c-omap.c
> > index ef73483..cdcdfeb 100644
> > --- a/drivers/i2c/busses/i2c-omap.c
> > +++ b/drivers/i2c/busses/i2c-omap.c
> > @@ -166,6 +166,8 @@ enum {
> >   #define SYSC_IDLEMODE_SMART		0x2
> >   #define SYSC_CLOCKACTIVITY_FCLK		0x2
> >
> > +/* Errata definitions */
> > +#define I2C_OMAP_ERRATA_I207		(1<<  0)
>                                          ^^^^
>                                tiny nit: s/1<</1 << (need a space)
> >
> >   struct omap_i2c_dev {
> >   	struct device		*dev;
> > @@ -199,6 +201,7 @@ struct omap_i2c_dev {
> >   	u16			bufstate;
> >   	u16			syscstate;
> >   	u16			westate;
> > +	u16			errata;
> overall I'd prefer the term quirk over errata - quirk is more of a 
> standard linux term used accross network, usb and other drivers, will 
> allow the code to be a little more familiar with the upstream 
> maintainers/reviewers.. but i leave it to tony and others to comment 
> more.. maybe it is just me being an ass again ;)
> 
> >   };
> >
> >   const static u8 reg_map[] = {
> > @@ -498,6 +501,11 @@ static int omap_i2c_init(struct 
> omap_i2c_dev *dev)
> >   	/* Take the I2C module out of reset: */
> >   	omap_i2c_write_reg(dev, OMAP_I2C_CON_REG, OMAP_I2C_CON_EN);
> >
> > +	dev->errata = 0;
> > +
> > +	if (cpu_is_omap2430() || cpu_is_omap34xx())
>                     ^^^^^^^^ wont cpu_is_omap24xx() cover omap2420 as 
> well? I think it might be better using that.. apologies on 
> missing it in 
> the last look.

This errata is not applicable for 2420 and it is applicable for:
1. omap2430 
2. omap34xx(including omap3630).

Sorry. My earlier patch was using this errata logic for all omap's 
except omap4 which was wrong(for omap2420 and omap1 - not sure, I don't have
any data hence ignoring this errata for omap1 also).

> 
> > +		dev->errata |= I2C_OMAP_ERRATA_I207;
> > +
> >   	/* Enable interrupts */
> >   	dev->iestate = (OMAP_I2C_IE_XRDY | OMAP_I2C_IE_RRDY |
> >   			OMAP_I2C_IE_ARDY | OMAP_I2C_IE_NACK |
> > @@ -695,6 +703,34 @@ omap_i2c_ack_stat(struct omap_i2c_dev 
> *dev, u16 stat)
> >   	omap_i2c_write_reg(dev, OMAP_I2C_STAT_REG, stat);
> >   }
> >
> > +static inline void i2c_omap_errata_i207(struct 
> omap_i2c_dev *dev, u16 stat)
> > +{
> > +	/*
> > +	 * I2C Errata(Errata Nos. OMAP2: 1.67, OMAP3: 1.8)
> > +	 * Not applicable for OMAP4.
> > +	 * Under certain rare conditions, RDR could be set again
> > +	 * when the bus is busy, then ignore the interrupt and
> > +	 * clear the interrupt.
> > +	 */
> > +	if (stat&  OMAP_I2C_STAT_RDR) {
> > +		/* Step 1: If RDR is set, clear it */
> > +		omap_i2c_ack_stat(dev, OMAP_I2C_STAT_RDR);
> > +
> > +		/* Step 2: */
> > +		if (!(omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG)
> > +						&  OMAP_I2C_STAT_BB)) {
> > +
> > +			/* Step 3: */
> > +			if (omap_i2c_read_reg(dev, OMAP_I2C_STAT_REG)
> > +						&  OMAP_I2C_STAT_RDR) {
> > +				omap_i2c_ack_stat(dev, 
> OMAP_I2C_STAT_RDR);
> > +				dev_dbg(dev->dev, "RDR when bus 
> is busy.\n");
> > +			}
> > +
> > +		}
> > +	}
> > +}
> > +
> >   /* rev1 devices are apparently only on some 15xx */
> >   #ifdef CONFIG_ARCH_OMAP15XX
> >
> > @@ -826,6 +862,10 @@ complete:
> >   		}
> >   		if (stat&  (OMAP_I2C_STAT_RRDY | OMAP_I2C_STAT_RDR)) {
> >   			u8 num_bytes = 1;
> > +
> > +			if (dev->errata&  I2C_OMAP_ERRATA_I207)
> > +				i2c_omap_errata_i207(dev, stat);
> > +
> >   			if (dev->fifo_size) {
> >   				if (stat&  OMAP_I2C_STAT_RRDY)
> >   					num_bytes = dev->fifo_size;
> 
> Thanks, sparse and checkpatch are happy now :)
> Regards,
> Nishanth Menon
> --
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