[Patch v2 1/2] 5200/mpc: improve i2c bus error recovery
Grant Likely
grant.likely at secretlab.ca
Thu Feb 18 07:10:25 EST 2010
On Wed, Feb 17, 2010 at 11:59 AM, Albrecht Dreß <albrecht.dress at arcor.de> 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 <albrecht.dress at arcor.de>
Acked-by: Grant Likely <grant.likely at secretlab.ca>
>
> ---
>
> 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!
>
>
> --- 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;
>
--
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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