Subject: Re: [Patch v2 1/2] 5200/mpc: improve i2c bus error recovery

From: "Ira W. Snyder" <[email-masked]>
Date: Wed, 5 May 2010 15:09:16 -0700

On Wed, Feb 17, 2010 at 07:59:14PM +0100, Albrecht Dreß wrote:
> This patch improves the recovery of the MPC's I2C bus from errors like bus
> hangs resulting in timeouts:
> 1. make the bus timeout configurable, as it depends on the bus clock and
>     the attached slave chip(s); default is still 1 second;
> 2. detect any of the cases indicated by the CF, BB and RXAK MSR flags if a
>     timeout occurs, and add a missing (required) MAL reset;
> 3. use a more reliable method to fixup the bus if a hang has been detected.
>     The sequence is sent 9 times which seems to be necessary if a slave
>     "misses" more than one clock cycle.  For 400 kHz bus speed, the fixup is
>     also ~70us (81us vs. 150us) faster.
> 
> Tested on a custom Lite5200b derived board, with a Dallas RTC, AD sensors
> and NXP IO expander chips attached to the i2c.
> 
> Changes vs. v1:
> - use improved bus fixup sequence for all chips (not only the 5200)
> - calculate real clock from defaults if no clock is given in the device tree
> - better description (I hope) of the changes.
> 
> I didn't split the changes in this file into three parts as recommended by
> Grant, as they actually belong together (i.e. they address one single
> problem, just in three places of one single source file).
> 
> Signed-off-by: Albrecht Dreß <[email-masked]>
> 
> ---
> 
> Note about the reset sequence: I verified the waveforms for 18.4kHz, 85.9kHz
> and 375kHz (drop me a note if you want to see scope screen shots).  Not
> verified on other mpc chips yet.
> @Ira: thanks in advance for giving it a try on your box!
> 

Did this series get forgotten about? I don't see it in bjdook's next-i2c
branch or in benh's next branch.

I've pulled these into my 2.6.31.13 kernel, and they seem to work fine.
You've got my Tested-by if you didn't get one from me already.

Ira

> --- linux-2.6.32-orig/drivers/i2c/busses/i2c-mpc.c	2009-12-03 04:51:21.000000000 +0100
> +++ linux-2.6.32/drivers/i2c/busses/i2c-mpc.c	2010-02-17 16:23:11.000000000 +0100
> @@ -59,6 +59,7 @@ struct mpc_i2c {
>   	wait_queue_head_t queue;
>   	struct i2c_adapter adap;
>   	int irq;
> +	u32 real_clk;
>   };
> 
>   struct mpc_i2c_divider {
> @@ -93,20 +94,23 @@ static irqreturn_t mpc_i2c_isr(int irq,
>   /* Sometimes 9th clock pulse isn't generated, and slave doesn't release
>    * the bus, because it wants to send ACK.
>    * Following sequence of enabling/disabling and sending start/stop generates
> - * the pulse, so it's all OK.
> + * the 9 pulses, so it's all OK.
>    */
>   static void mpc_i2c_fixup(struct mpc_i2c *i2c)
>   {
> -	writeccr(i2c, 0);
> -	udelay(30);
> -	writeccr(i2c, CCR_MEN);
> -	udelay(30);
> -	writeccr(i2c, CCR_MSTA | CCR_MTX);
> -	udelay(30);
> -	writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> -	udelay(30);
> -	writeccr(i2c, CCR_MEN);
> -	udelay(30);
> +	int k;
> +	u32 delay_val = 1000000 / i2c->real_clk + 1;
> +
> +	if (delay_val < 2)
> +		delay_val = 2;
> +
> +	for (k = 9; k; k--) {
> +		writeccr(i2c, 0);
> +		writeccr(i2c, CCR_MSTA | CCR_MTX | CCR_MEN);
> +		udelay(delay_val);
> +		writeccr(i2c, CCR_MEN);
> +		udelay(delay_val << 1);
> +	}
>   }
> 
>   static int i2c_wait(struct mpc_i2c *i2c, unsigned timeout, int writing)
> @@ -186,15 +190,19 @@ static const struct mpc_i2c_divider mpc_
>   	{10240, 0x9d}, {12288, 0x9e}, {15360, 0x9f}
>   };
> 
> -int mpc_i2c_get_fdr_52xx(struct device_node *node, u32 clock, int prescaler)
> +int mpc_i2c_get_fdr_52xx(struct device_node *node, u32 clock, int prescaler,
> +			 u32 *real_clk)
>   {
>   	const struct mpc_i2c_divider *div = NULL;
>   	unsigned int pvr = mfspr(SPRN_PVR);
>   	u32 divider;
>   	int i;
> 
> -	if (!clock)
> +	if (!clock) {
> +		/* see below - default fdr = 0x3f -> div = 2048 */
> +		*real_clk = mpc5xxx_get_bus_frequency(node) / 2048;
>   		return -EINVAL;
> +	}
> 
>   	/* Determine divider value */
>   	divider = mpc5xxx_get_bus_frequency(node) / clock;
> @@ -212,7 +220,8 @@ int mpc_i2c_get_fdr_52xx(struct device_n
>   			break;
>   	}
> 
> -	return div ? (int)div->fdr : -EINVAL;
> +	*real_clk = mpc5xxx_get_bus_frequency(node) / div->divider;
> +	return (int)div->fdr;
>   }
> 
>   static void mpc_i2c_setclock_52xx(struct device_node *node,
> @@ -221,13 +230,14 @@ static void mpc_i2c_setclock_52xx(struct
>   {
>   	int ret, fdr;
> 
> -	ret = mpc_i2c_get_fdr_52xx(node, clock, prescaler);
> +	ret = mpc_i2c_get_fdr_52xx(node, clock, prescaler, &i2c->real_clk);
>   	fdr = (ret >= 0) ? ret : 0x3f; /* backward compatibility */
> 
>   	writeb(fdr & 0xff, i2c->base + MPC_I2C_FDR);
> 
>   	if (ret >= 0)
> -		dev_info(i2c->dev, "clock %d Hz (fdr=%d)\n", clock, fdr);
> +		dev_info(i2c->dev, "clock %u Hz (fdr=%d)\n", i2c->real_clk,
> +			 fdr);
>   }
>   #else /* !CONFIG_PPC_MPC52xx */
>   static void mpc_i2c_setclock_52xx(struct device_node *node,
> @@ -287,14 +297,18 @@ u32 mpc_i2c_get_sec_cfg_8xxx(void)
>   	return val;
>   }
> 
> -int mpc_i2c_get_fdr_8xxx(struct device_node *node, u32 clock, u32 prescaler)
> +int mpc_i2c_get_fdr_8xxx(struct device_node *node, u32 clock, u32 prescaler,
> +			 u32 *real_clk)
>   {
>   	const struct mpc_i2c_divider *div = NULL;
>   	u32 divider;
>   	int i;
> 
> -	if (!clock)
> +	if (!clock) {
> +		/* see below - default fdr = 0x1031 -> div = 16 * 3072 */
> +		*real_clk = fsl_get_sys_freq() / prescaler / (16 * 3072);
>   		return -EINVAL;
> +	}
> 
>   	/* Determine proper divider value */
>   	if (of_device_is_compatible(node, "fsl,mpc8544-i2c"))
> @@ -317,6 +331,7 @@ int mpc_i2c_get_fdr_8xxx(struct device_n
>   			break;
>   	}
> 
> +	*real_clk = fsl_get_sys_freq() / prescaler / div->divider;
>   	return div ? (int)div->fdr : -EINVAL;
>   }
> 
> @@ -326,7 +341,7 @@ static void mpc_i2c_setclock_8xxx(struct
>   {
>   	int ret, fdr;
> 
> -	ret = mpc_i2c_get_fdr_8xxx(node, clock, prescaler);
> +	ret = mpc_i2c_get_fdr_8xxx(node, clock, prescaler, &i2c->real_clk);
>   	fdr = (ret >= 0) ? ret : 0x1031; /* backward compatibility */
> 
>   	writeb(fdr & 0xff, i2c->base + MPC_I2C_FDR);
> @@ -334,7 +349,7 @@ static void mpc_i2c_setclock_8xxx(struct
> 
>   	if (ret >= 0)
>   		dev_info(i2c->dev, "clock %d Hz (dfsrr=%d fdr=%d)\n",
> -			 clock, fdr >> 8, fdr & 0xff);
> +			 i2c->real_clk, fdr >> 8, fdr & 0xff);
>   }
> 
>   #else /* !CONFIG_FSL_SOC */
> @@ -446,10 +461,14 @@ static int mpc_xfer(struct i2c_adapter *
>   			return -EINTR;
>   		}
>   		if (time_after(jiffies, orig_jiffies + HZ)) {
> +			u8 status = readb(i2c->base + MPC_I2C_SR);
> +
>   			dev_dbg(i2c->dev, "timeout\n");
> -			if (readb(i2c->base + MPC_I2C_SR) ==
> -			    (CSR_MCF | CSR_MBB | CSR_RXAK))
> +			if ((status & (CSR_MCF | CSR_MBB | CSR_RXAK)) != 0) {
> +				writeb(status & ~CSR_MAL,
> +				       i2c->base + MPC_I2C_SR);
>   				mpc_i2c_fixup(i2c);
> +			}
>   			return -EIO;
>   		}
>   		schedule();
> @@ -540,6 +559,14 @@ static int __devinit fsl_i2c_probe(struc
>   		}
>   	}
> 
> +	prop = of_get_property(op->node, "fsl,timeout", &plen);
> +	if (prop && plen == sizeof(u32)) {
> +		mpc_ops.timeout = *prop * HZ / 1000000;
> +		if (mpc_ops.timeout < 5)
> +			mpc_ops.timeout = 5;
> +	}
> +	dev_info(i2c->dev, "timeout %u us\n", mpc_ops.timeout * 1000000 / HZ);
> +
>   	dev_set_drvdata(&op->dev, i2c);
> 
>   	i2c->adap = mpc_ops;
>