| Message ID | 3778fa75-0327-0c36-1721-e89e23a782b6@ergon.ch (mailing list archive) |
|---|---|
| State | New, archived |
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Hi Claudio, On Tue, Sep 26, 2017 at 02:24:59PM +0200, Claudio Foellmi wrote: > On 19.09.2017 12:50, Vignesh R wrote: > > > > > > On Monday 18 September 2017 05:31 PM, Claudio Foellmi wrote: > >> On 18.09.2017 07:24, Vignesh R wrote: > >>> > >>> > >>> On Saturday 16 September 2017 05:01 AM, Strashko, Grygorii wrote: > >>>> > >>>> > >>>> On 09/14/2017 10:39 AM, Claudio Foellmi wrote: > >>>>> A very conservative check for bus activity (to prevent interference > >>>>> in multimaster setups) prevented the bus recovery methods from being > >>>>> triggered in the case that SDA or SCL was stuck low. > >>>>> This defeats the purpose of the recovery mechanism, which was introduced > >>>>> for exactly this situation (a slave device keeping SDA pulled down). > >>>>> > >>>>> Note that bus lockups can persist across reboots. The only other options > >>>>> are to reset or power cycle the offending slave device, and many i2c > >>>>> slaves do not even have a reset pin. > >>>>> > >>>>> If we see that one of the lines is low for the entire timeout duration, > >>>>> we can actually be sure that there is no other master driving the bus. > >>>>> It is therefore save for us to attempt a bus recovery. > >>>>> > >>>> > >>>> Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com> > >>>> > >>>>> Signed-off-by: Claudio Foellmi <claudio.foellmi@ergon.ch> > >>>>> --- > >>>>> Caveat: It turns out I don't have the hardware to fully test the > >>>>> recovery mechanism. My faulty i2c slave device actually pulls down SCL, > >>>>> not SDA (so the recovery will not succeed in my case). > >>> > >>> Maybe, you could detect SCL stuck low case by reading status of SCL line > >>> from OMAP_I2C_SYSTEST_REG and then call IP reset (there is nothing much > >>> that can be done) instead of bus recovery. > >>> > >> > >> I plan on posting a related patch soon, that will print better messages > >> if the generic recovery fails. If SCL is stuck low, I think the best we > >> can do is make the problem visible in the kernel log. > >> > >>>>> But by directly connecting SDA to ground, I could at least make sure > >>>>> the recovery function gets called after applying this patch. > >>>>> > >>> > >>> I had seen flood of XRDY & RRDY interrupts as soon as TMODE is set to > >>> 0x3 as part of omap_i2c_prepare_recovery() leading to unusable system. > >>> Did you observe this behavior on your system? Could you mention the > >>> platform on which this experiment done? > >>> > >> > >> So attempting bus recovery is dangerous on some platforms? > >> I did not notice any obvious problems (assuming an 'unusable system' > >> would be hard to miss), but then again I only have one target to test on. > >> I'm working with a TI AM3352, the slave is a NXP NT3H2211 on i2c-1. > >> > > > > I hit a situation where when communicating with a faulty i2c device, the > > last transaction on the bus does not end with proper STOP condition on > > the i2c bus. Since, STOP condition was not detected by IP, Bus Busy will > > remain set even though both SCL and SDA are high. Thus, > > omap_i2c_wait_for_bb() function would end up calling bus recovery. And > > as soon as TMODE is set to 0x3 and ST_EN to 0x1, there is a flood of > > XRDY & RRDY interrupts. > > > > This spurious irqs can be reproduced easily by setting TMODE to 0x3 and > > ST_EN to 0x1 in OMAP_I2C_SYSTEST_REG when both SCL and SDA are high (bus > > is idle) even on AM335x. > > > > So, if you are not seeing irq flood when SCL/SDA is stuck low, then > > maybe its safe to enter TMODE 0x3 in such cases. Could you modify the > > patch to test whether or not SDA is stuck low before initiating bus > > recovery? > > > > This sounds more like a problem with the interrupt handler than with > bus recovery, so I'm a bit hesitant to just add such a workaround. > Instead, I spent a few hours looking through the interrupt handling > (and poking my i2c bus with a wire to induce random faults), and > I suspect to have found the underlying cause, or at least part of it: > > We sometimes ignore some interrupts (such as RRDY if we think we are > not in receiving mode), but don't really deal with their cause. > As a result, the same interrupt will just be raised again as soon as > we leave the handler. It will then be ignored again, and raised again... > > I'm still not quite sure how we can reliably get into such situations in > the first place, but not sending a stop condition seems to be part of it. > Maybe it is somehow connected to the automatic internal state change > that happens as part of AL or NACK interrupts. > > > Below is a small patch that should test my assumptions. > It clears the incoming fifo and acks the ignored RRDY interrupts. > > Sebastian, can you please check if this helps with your problems on N950? > If it does, I'll turn it into a proper standalone patch. No, it does not. Also no interrupts ignoring messages appearing in dmesg: n950# dmesg | grep -E "48072000.i2c|lp5523x" [ 0.791046] omap_i2c 48072000.i2c: bus 1 rev4.4 at 400 kHz [ 4.934265] lp5523x 1-0032: reset command sent (no ACK)! [ 6.003875] omap_i2c 48072000.i2c: controller timed out [ 6.033874] lp5523x 1-0032: device detection err: -110 [ 6.039154] lp5523x: probe of 1-0032 failed with error -110 -- Sebastian
On 29.09.2017 14:52, Sebastian Reichel wrote: > Hi Claudio, > > On Tue, Sep 26, 2017 at 02:24:59PM +0200, Claudio Foellmi wrote: >> On 19.09.2017 12:50, Vignesh R wrote: >>> >>> >>> On Monday 18 September 2017 05:31 PM, Claudio Foellmi wrote: >>>> On 18.09.2017 07:24, Vignesh R wrote: >>>>> >>>>> >>>>> On Saturday 16 September 2017 05:01 AM, Strashko, Grygorii wrote: >>>>>> >>>>>> >>>>>> On 09/14/2017 10:39 AM, Claudio Foellmi wrote: >>>>>>> A very conservative check for bus activity (to prevent interference >>>>>>> in multimaster setups) prevented the bus recovery methods from being >>>>>>> triggered in the case that SDA or SCL was stuck low. >>>>>>> This defeats the purpose of the recovery mechanism, which was introduced >>>>>>> for exactly this situation (a slave device keeping SDA pulled down). >>>>>>> >>>>>>> Note that bus lockups can persist across reboots. The only other options >>>>>>> are to reset or power cycle the offending slave device, and many i2c >>>>>>> slaves do not even have a reset pin. >>>>>>> >>>>>>> If we see that one of the lines is low for the entire timeout duration, >>>>>>> we can actually be sure that there is no other master driving the bus. >>>>>>> It is therefore save for us to attempt a bus recovery. >>>>>>> >>>>>> >>>>>> Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com> >>>>>> >>>>>>> Signed-off-by: Claudio Foellmi <claudio.foellmi@ergon.ch> >>>>>>> --- >>>>>>> Caveat: It turns out I don't have the hardware to fully test the >>>>>>> recovery mechanism. My faulty i2c slave device actually pulls down SCL, >>>>>>> not SDA (so the recovery will not succeed in my case). >>>>> >>>>> Maybe, you could detect SCL stuck low case by reading status of SCL line >>>>> from OMAP_I2C_SYSTEST_REG and then call IP reset (there is nothing much >>>>> that can be done) instead of bus recovery. >>>>> >>>> >>>> I plan on posting a related patch soon, that will print better messages >>>> if the generic recovery fails. If SCL is stuck low, I think the best we >>>> can do is make the problem visible in the kernel log. >>>> >>>>>>> But by directly connecting SDA to ground, I could at least make sure >>>>>>> the recovery function gets called after applying this patch. >>>>>>> >>>>> >>>>> I had seen flood of XRDY & RRDY interrupts as soon as TMODE is set to >>>>> 0x3 as part of omap_i2c_prepare_recovery() leading to unusable system. >>>>> Did you observe this behavior on your system? Could you mention the >>>>> platform on which this experiment done? >>>>> >>>> >>>> So attempting bus recovery is dangerous on some platforms? >>>> I did not notice any obvious problems (assuming an 'unusable system' >>>> would be hard to miss), but then again I only have one target to test on. >>>> I'm working with a TI AM3352, the slave is a NXP NT3H2211 on i2c-1. >>>> >>> >>> I hit a situation where when communicating with a faulty i2c device, the >>> last transaction on the bus does not end with proper STOP condition on >>> the i2c bus. Since, STOP condition was not detected by IP, Bus Busy will >>> remain set even though both SCL and SDA are high. Thus, >>> omap_i2c_wait_for_bb() function would end up calling bus recovery. And >>> as soon as TMODE is set to 0x3 and ST_EN to 0x1, there is a flood of >>> XRDY & RRDY interrupts. >>> >>> This spurious irqs can be reproduced easily by setting TMODE to 0x3 and >>> ST_EN to 0x1 in OMAP_I2C_SYSTEST_REG when both SCL and SDA are high (bus >>> is idle) even on AM335x. >>> >>> So, if you are not seeing irq flood when SCL/SDA is stuck low, then >>> maybe its safe to enter TMODE 0x3 in such cases. Could you modify the >>> patch to test whether or not SDA is stuck low before initiating bus >>> recovery? >>> >> >> This sounds more like a problem with the interrupt handler than with >> bus recovery, so I'm a bit hesitant to just add such a workaround. >> Instead, I spent a few hours looking through the interrupt handling >> (and poking my i2c bus with a wire to induce random faults), and >> I suspect to have found the underlying cause, or at least part of it: >> >> We sometimes ignore some interrupts (such as RRDY if we think we are >> not in receiving mode), but don't really deal with their cause. >> As a result, the same interrupt will just be raised again as soon as >> we leave the handler. It will then be ignored again, and raised again... >> >> I'm still not quite sure how we can reliably get into such situations in >> the first place, but not sending a stop condition seems to be part of it. >> Maybe it is somehow connected to the automatic internal state change >> that happens as part of AL or NACK interrupts. >> >> >> Below is a small patch that should test my assumptions. >> It clears the incoming fifo and acks the ignored RRDY interrupts. >> >> Sebastian, can you please check if this helps with your problems on N950? >> If it does, I'll turn it into a proper standalone patch. > > No, it does not. Also no interrupts ignoring messages appearing > in dmesg: > > n950# dmesg | grep -E "48072000.i2c|lp5523x" > [ 0.791046] omap_i2c 48072000.i2c: bus 1 rev4.4 at 400 kHz > [ 4.934265] lp5523x 1-0032: reset command sent (no ACK)! > [ 6.003875] omap_i2c 48072000.i2c: controller timed out > [ 6.033874] lp5523x 1-0032: device detection err: -110 > [ 6.039154] lp5523x: probe of 1-0032 failed with error -110 > Hi Sebastian Thank you for trying it out. It seems that your symptoms are quite different from the ones that Vignesh described earlier. He had never-ending storms of spurious interrupts (which that patch would have addressed), but you don't seem to get any interrupts at all. Not even the NACK one, which just looks wrong. If you want to still dig deeper, you can enable debug logs for i2c-omap, so you can see every single interrupt. But if there are none, I don't see what we could possibly do to fix it. Vignesh, do you still have access to any of those devices with interrupt floods? If so, could you try the previous patch on one of them? Also note that Sebastian's issue is definitely not caused (or helped) by bus recovery, the timeout he sees resets the adapter right away. So he is not affected by my original patch either way. -- Claudio -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Hi, On Fri, Sep 29, 2017 at 05:17:47PM +0200, Claudio Foellmi wrote: > >> Sebastian, can you please check if this helps with your problems on N950? > >> If it does, I'll turn it into a proper standalone patch. > > > > No, it does not. Also no interrupts ignoring messages appearing > > in dmesg: > > > > n950# dmesg | grep -E "48072000.i2c|lp5523x" > > [ 0.791046] omap_i2c 48072000.i2c: bus 1 rev4.4 at 400 kHz > > [ 4.934265] lp5523x 1-0032: reset command sent (no ACK)! > > [ 6.003875] omap_i2c 48072000.i2c: controller timed out > > [ 6.033874] lp5523x 1-0032: device detection err: -110 > > [ 6.039154] lp5523x: probe of 1-0032 failed with error -110 > > > > Hi Sebastian > > Thank you for trying it out. > It seems that your symptoms are quite different from the ones that Vignesh > described earlier. He had never-ending storms of spurious interrupts > (which that patch would have addressed), but you don't seem to get > any interrupts at all. Not even the NACK one, which just looks wrong. > > If you want to still dig deeper, you can enable debug logs for i2c-omap, > so you can see every single interrupt. But if there are none, I don't see > what we could possibly do to fix it. > > > Vignesh, do you still have access to any of those devices with interrupt > floods? If so, could you try the previous patch on one of them? > > Also note that Sebastian's issue is definitely not caused (or helped) > by bus recovery, the timeout he sees resets the adapter right away. > So he is not affected by my original patch either way. > > -- Claudio Yeah, I don't see IRQ storm, so this might be a different issue. FWIW this is what I see on N950: n950# dmesg | grep -E "48072000.i2c|lp55" [ 2.136383] omap_i2c 48072000.i2c: bus 1 rev4.4 at 400 kHz [ 8.212951] omap_i2c 48072000.i2c: addr: 0x0032, len: 2, flags: 0x0, stop: 1 [ 8.213287] omap_i2c 48072000.i2c: IRQ (ISR = 0x0010) [ 8.213592] omap_i2c 48072000.i2c: IRQ (ISR = 0x0002) [ 8.213897] lp5523x 1-0032: reset command sent (no ACK)! [ 8.242462] omap_i2c 48072000.i2c: addr: 0x0032, len: 2, flags: 0x0, stop: 1 [ 8.243255] omap_i2c 48072000.i2c: IRQ (ISR = 0x0014) [ 8.243469] omap_i2c 48072000.i2c: IRQ (ISR = 0x0010) [ 8.253387] omap_i2c 48072000.i2c: addr: 0x0032, len: 1, flags: 0x0, stop: 0 [ 8.253631] omap_i2c 48072000.i2c: IRQ (ISR = 0x0010) [ 9.272735] omap_i2c 48072000.i2c: controller timed out [ 9.278167] lp5523x 1-0032: device detection err: -110 [ 9.283843] lp5523x: probe of 1-0032 failed with error -110 [ 9.662780] omap_i2c 48072000.i2c: addr: 0x0060, len: 1, flags: 0x0, stop: 0 [ 9.670166] omap_i2c 48072000.i2c: IRQ (ISR = 0x0010) [ 9.675659] omap_i2c 48072000.i2c: IRQ (ISR = 0x0004) [ 9.682617] omap_i2c 48072000.i2c: addr: 0x0060, len: 1, flags: 0x1, stop: 1 [ 9.689819] omap_i2c 48072000.i2c: IRQ (ISR = 0x0008) [ 9.695007] omap_i2c 48072000.i2c: IRQ (ISR = 0x0004) -- Sebastian
On Friday 29 September 2017 08:47 PM, Claudio Foellmi wrote: [...] >>>> I hit a situation where when communicating with a faulty i2c device, the >>>> last transaction on the bus does not end with proper STOP condition on >>>> the i2c bus. Since, STOP condition was not detected by IP, Bus Busy will >>>> remain set even though both SCL and SDA are high. Thus, >>>> omap_i2c_wait_for_bb() function would end up calling bus recovery. And >>>> as soon as TMODE is set to 0x3 and ST_EN to 0x1, there is a flood of >>>> XRDY & RRDY interrupts. >>>> >>>> This spurious irqs can be reproduced easily by setting TMODE to 0x3 and >>>> ST_EN to 0x1 in OMAP_I2C_SYSTEST_REG when both SCL and SDA are high (bus >>>> is idle) even on AM335x. >>>> >>>> So, if you are not seeing irq flood when SCL/SDA is stuck low, then >>>> maybe its safe to enter TMODE 0x3 in such cases. Could you modify the >>>> patch to test whether or not SDA is stuck low before initiating bus >>>> recovery? >>>> >>> >>> This sounds more like a problem with the interrupt handler than with >>> bus recovery, so I'm a bit hesitant to just add such a workaround. I would not say its a workaround. As per I2C spec, bus recovery is to be tried only when SDA is stuck low. My suggestion is to check this condition before requesting recovery. >>> Instead, I spent a few hours looking through the interrupt handling >>> (and poking my i2c bus with a wire to induce random faults), and >>> I suspect to have found the underlying cause, or at least part of it: >>> >>> We sometimes ignore some interrupts (such as RRDY if we think we are >>> not in receiving mode), but don't really deal with their cause. >>> As a result, the same interrupt will just be raised again as soon as >>> we leave the handler. It will then be ignored again, and raised again... >>> >>> I'm still not quite sure how we can reliably get into such situations in >>> the first place, but not sending a stop condition seems to be part of it. >>> Maybe it is somehow connected to the automatic internal state change >>> that happens as part of AL or NACK interrupts. >>> >>> >>> Below is a small patch that should test my assumptions. >>> It clears the incoming fifo and acks the ignored RRDY interrupts. >>> >>> Sebastian, can you please check if this helps with your problems on N950? >>> If it does, I'll turn it into a proper standalone patch. >> >> No, it does not. Also no interrupts ignoring messages appearing >> in dmesg: >> >> n950# dmesg | grep -E "48072000.i2c|lp5523x" >> [ 0.791046] omap_i2c 48072000.i2c: bus 1 rev4.4 at 400 kHz >> [ 4.934265] lp5523x 1-0032: reset command sent (no ACK)! >> [ 6.003875] omap_i2c 48072000.i2c: controller timed out >> [ 6.033874] lp5523x 1-0032: device detection err: -110 >> [ 6.039154] lp5523x: probe of 1-0032 failed with error -110 >> > > Hi Sebastian > > Thank you for trying it out. > It seems that your symptoms are quite different from the ones that Vignesh > described earlier. He had never-ending storms of spurious interrupts > (which that patch would have addressed), but you don't seem to get > any interrupts at all. Not even the NACK one, which just looks wrong. > > If you want to still dig deeper, you can enable debug logs for i2c-omap, > so you can see every single interrupt. But if there are none, I don't see > what we could possibly do to fix it. > > > Vignesh, do you still have access to any of those devices with interrupt > floods? If so, could you try the previous patch on one of them? In past, I had tried to ACK all the IRQs instead of ignoring, but that did not help. Anyway, I tried your patch, but unfortunately that does not help either. I see interrupts being ignored, but the IRQ flood continues. Here is the log: http://pastebin.ubuntu.com/25666141/ > > Also note that Sebastian's issue is definitely not caused (or helped) > by bus recovery, the timeout he sees resets the adapter right away. > So he is not affected by my original patch either way. > > -- Claudio >
diff --git a/drivers/i2c/busses/i2c-omap.c b/drivers/i2c/busses/i2c-omap.c index 1ebb5e9..1ad1b0c 100644 --- a/drivers/i2c/busses/i2c-omap.c +++ b/drivers/i2c/busses/i2c-omap.c @@ -1009,6 +1009,7 @@ omap_i2c_isr_thread(int this_irq, void *dev_id) struct omap_i2c_dev *omap = dev_id; u16 bits; u16 stat; + u16 buf; int err = 0, count = 0; do { @@ -1016,11 +1017,21 @@ omap_i2c_isr_thread(int this_irq, void *dev_id) stat = omap_i2c_read_reg(omap, OMAP_I2C_STAT_REG); stat &= bits; - /* If we're in receiver mode, ignore XDR/XRDY */ - if (omap->receiver) + /* If we're in receiver mode, ignore XDR/XRDY and vice versa */ + if (omap->receiver && stat & (OMAP_I2C_STAT_XDR | + OMAP_I2C_STAT_XRDY)) { + dev_err(omap->dev, "ignoring TX interrupts\n"); stat &= ~(OMAP_I2C_STAT_XDR | OMAP_I2C_STAT_XRDY); - else + } else if (!omap->receiver && stat & (OMAP_I2C_STAT_RDR | + OMAP_I2C_STAT_RRDY)) { + dev_err(omap->dev, "ignoring RX interrupts\n"); stat &= ~(OMAP_I2C_STAT_RDR | OMAP_I2C_STAT_RRDY); + buf = omap_i2c_read_reg(omap, OMAP_I2C_BUF_REG); + buf |= OMAP_I2C_BUF_RXFIF_CLR; + omap_i2c_write_reg(omap, OMAP_I2C_BUF_REG, buf); + omap_i2c_ack_stat(omap, + OMAP_I2C_STAT_RRDY | OMAP_I2C_STAT_RDR); + } if (!stat) { /* my work here is done */