Hi Grant & Ira: Thanks a lot for reviewing the patch, and for the encouraging comments! I will re-submit a new version according according to them, hopefully tomorrow or on Thursday.
Best, Albrecht. ----- Original Nachricht ---- Von: Grant Likely <[email protected]> An: Albrecht Dreß <[email protected]> Datum: 16.02.2010 20:31 Betreff: Re: [PATCH/RFC 1/2] 5200: improve i2c bus error recovery > Hi Albrecht, > > Comments below. > > On Fri, Jan 22, 2010 at 1:17 PM, Albrecht Dreß <[email protected]> > wrote: > > Improve the recovery of the MPC5200B's I2C bus from errors like bus > > hangs. > > > > Signed-off-by: Albrecht Dreß <[email protected]> > > > > --- > > > > This patch introduces several improvements to the MPC5200B's I2C driver > > as to improve the recovery from error conditions I encountered when > > testing a custom board with several I2C devices attached (eeprom, io > > expander, rtc, sensors). The error conditions included cases where the > > bus if logic of one slave apparently went south, blocking the bus > > completely. > > > > My fixes include: > > 1. make the bus timeout configurable in fsl_i2c_probe(); the default of > > one second is *way* too long for my use case; > > 2. if a timeout condition occurs in mpc_xfer(), mpc_i2c_fixup() the bus > > if *any* of the CF, BB and RXAK flags in the MSR is 1. I actually > > saw different combinations with hangs, not only all three set; > > 3. improve the fixup procedure by calculating the timing needed from the > > real (configured) bus clock, calculated in mpc_i2c_setclock_52xx(). > > Furthermore, I issue 9 instead of one cycle, as I experienced cases > > where the single one is not enough (found this tip in a forum). As a > > side effect, the new scheme needs only 81us @375kHz bus clock instead > > of 150us. I recorded waveforms for 18.4kHz, 85.9kHz and 375kHz, all > > looking fine, which I can provide if anyone is interested. > > These are three separate fixes. Ideally you should submit them in > separate patches to make it easy on poor old reviewers like me. And, > as Ben mentions, this descriptions should be above the '---' line so > it appears in the commit text. OK, will do. > > > > > Open questions: > > - is the approach correct at all, in particular the interpretation of > > the flags (#2)? > > - could this code also be used on non-5200 processors? > > > > --- 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 2010-01-22 > 16:05:13.000000000 +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 { > > @@ -97,16 +98,32 @@ static irqreturn_t mpc_i2c_isr(int irq, > > */ > > 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); > > + if (i2c->real_clk == 0) { > > + 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); > > + } else { > > + 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); > > + } > > + } > > This doesn't look right. Why is the old code being preserved? Isn't > it not as reliable? It looks to me that the new block should be the > only path, with delay_val getting hard set to a sane value if real_clk > == 0. This approach looks to add complexity to the driver without a > reason other than fear it *might* breaking something. > > If the new code is better, then be strong, stand tall, and say in a > loud voice, "this old code is crap. The new stuff is much better." :-) Ok... > > g. > > > } > > > > static int i2c_wait(struct mpc_i2c *i2c, unsigned timeout, int writing) > > @@ -186,15 +203,18 @@ 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) { > > + *real_clk = 0; > > return -EINVAL; > > + } > > > > /* Determine divider value */ > > divider = mpc5xxx_get_bus_frequency(node) / clock; > > @@ -212,7 +232,8 @@ 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 +242,14 @@ 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, > > @@ -446,10 +468,14 @@ 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 +566,14 @@ static int __devinit fsl_i2c_probe(struc > > } > > } > > > > + prop = of_get_property(op->node, "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; > > > > _______________________________________________ > > devicetree-discuss mailing list > > [email protected] > > https://lists.ozlabs.org/listinfo/devicetree-discuss > > > > > > -- > Grant Likely, B.Sc., P.Eng. > Secret Lab Technologies Ltd. > _______________________________________________ > Linuxppc-dev mailing list > [email protected] > https://lists.ozlabs.org/listinfo/linuxppc-dev > Immer auf dem Laufenden! 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