Re: fsl_espi errors on v5.7.15

[Nicholas Piggin <npiggin@xxxxxxxxx>]

Excerpts from Chris Packham's message of August 28, 2020 8:07 am:
> On 27/08/20 7:12 pm, Nicholas Piggin wrote:
>> Excerpts from Heiner Kallweit's message of August 26, 2020 4:38 pm:
>>> On 26.08.2020 08:07, Chris Packham wrote:
>>>> On 26/08/20 1:48 pm, Chris Packham wrote:
>>>>> On 26/08/20 10:22 am, Chris Packham wrote:
>>>>>> On 25/08/20 7:22 pm, Heiner Kallweit wrote:
>>>>>>
>>>>>> <snip>
>>>>>>> I've been staring at spi-fsl-espi.c for while now and I think I've
>>>>>>>> identified a couple of deficiencies that may or may not be related
>>>>>>>> to my
>>>>>>>> issue.
>>>>>>>>
>>>>>>>> First I think the 'Transfer done but SPIE_DON isn't set' message
>>>>>>>> can be
>>>>>>>> generated spuriously. In fsl_espi_irq() we read the ESPI_SPIE
>>>>>>>> register.
>>>>>>>> We also write back to it to clear the current events. We re-read it in
>>>>>>>> fsl_espi_cpu_irq() and complain when SPIE_DON is not set. But we can
>>>>>>>> naturally end up in that situation if we're doing a large read.
>>>>>>>> Consider
>>>>>>>> the messages for reading a block of data from a spi-nor chip
>>>>>>>>
>>>>>>>>     tx = READ_OP + ADDR
>>>>>>>>     rx = data
>>>>>>>>
>>>>>>>> We setup the transfer and pump out the tx_buf. The first interrupt
>>>>>>>> goes
>>>>>>>> off and ESPI_SPIE has SPIM_DON and SPIM_RXT set. We empty the rx fifo,
>>>>>>>> clear ESPI_SPIE and wait for the next interrupt. The next interrupt
>>>>>>>> fires and this time we have ESPI_SPIE with just SPIM_RXT set. This
>>>>>>>> continues until we've received all the data and we finish with
>>>>>>>> ESPI_SPIE
>>>>>>>> having only SPIM_RXT set. When we re-read it we complain that SPIE_DON
>>>>>>>> isn't set.
>>>>>>>>
>>>>>>>> The other deficiency is that we only get an interrupt when the
>>>>>>>> amount of
>>>>>>>> data in the rx fifo is above FSL_ESPI_RXTHR. If there are fewer than
>>>>>>>> FSL_ESPI_RXTHR left to be received we will never pull them out of
>>>>>>>> the fifo.
>>>>>>>>
>>>>>>> SPIM_DON will trigger an interrupt once the last characters have been
>>>>>>> transferred, and read the remaining characters from the FIFO.
>>>>>> The T2080RM that I have says the following about the DON bit
>>>>>>
>>>>>> "Last character was transmitted. The last character was transmitted
>>>>>> and a new command can be written for the next frame."
>>>>>>
>>>>>> That does at least seem to fit with my assertion that it's all about
>>>>>> the TX direction. But the fact that it doesn't happen all the time
>>>>>> throws some doubt on it.
>>>>>>
>>>>>>> I think the reason I'm seeing some variability is because of how fast
>>>>>>>> (or slow) the interrupts get processed and how fast the spi-nor
>>>>>>>> chip can
>>>>>>>> fill the CPUs rx fifo.
>>>>>>>>
>>>>>>> To rule out timing issues at high bus frequencies I initially asked
>>>>>>> for re-testing at lower frequencies. If you e.g. limit the bus to 1 MHz
>>>>>>> or even less, then timing shouldn't be an issue.
>>>>>> Yes I've currently got spi-max-frequency = <1000000>; in my dts. I
>>>>>> would also expect a slower frequency would fit my "DON is for TX"
>>>>>> narrative.
>>>>>>> Last relevant functional changes have been done almost 4 years ago.
>>>>>>> And yours is the first such report I see. So question is what could
>>>>>>> be so
>>>>>>> special with your setup that it seems you're the only one being
>>>>>>> affected.
>>>>>>> The scenarios you describe are standard, therefore much more people
>>>>>>> should be affected in case of a driver bug.
>>>>>> Agreed. But even on my hardware (which may have a latent issue
>>>>>> despite being in the field for going on 5 years) the issue only
>>>>>> triggers under some fairly specific circumstances.
>>>>>>> You said that kernel config impacts how frequently the issue happens.
>>>>>>> Therefore question is what's the diff in kernel config, and how could
>>>>>>> the differences be related to SPI.
>>>>>> It did seem to be somewhat random. Things like CONFIG_PREEMPT have an
>>>>>> impact but every time I found something that seemed to be having an
>>>>>> impact I've been able to disprove it. I actually think its about how
>>>>>> busy the system is which may or may not affect when we get round to
>>>>>> processing the interrupts.
>>>>>>
>>>>>> I have managed to get the 'Transfer done but SPIE_DON isn't set!' to
>>>>>> occur on the T2080RDB.
>>>>>>
>>>>>> I've had to add the following to expose the environment as a mtd
>>>>>> partition
>>>>>>
>>>>>> diff --git a/arch/powerpc/boot/dts/fsl/t208xrdb.dtsi
>>>>>> b/arch/powerpc/boot/dts/fsl/t208xrdb.dtsi
>>>>>> index ff87e67c70da..fbf95fc1fd68 100644
>>>>>> --- a/arch/powerpc/boot/dts/fsl/t208xrdb.dtsi
>>>>>> +++ b/arch/powerpc/boot/dts/fsl/t208xrdb.dtsi
>>>>>> @@ -116,6 +116,15 @@ flash@0 {
>>>>>>                                  compatible = "micron,n25q512ax3",
>>>>>> "jedec,spi-nor";
>>>>>>                                  reg = <0>;
>>>>>>                                  spi-max-frequency = <10000000>; /*
>>>>>> input clock */
>>>>>> +
>>>>>> +                               partition@u-boot {
>>>>>> +                                        reg = <0x00000000 0x00100000>;
>>>>>> +                                        label = "u-boot";
>>>>>> +                                };
>>>>>> +                                partition@u-boot-env {
>>>>>> +                                        reg = <0x00100000 0x00010000>;
>>>>>> +                                        label = "u-boot-env";
>>>>>> +                                };
>>>>>>                          };
>>>>>>                  };
>>>>>>
>>>>>> And I'm using the following script to poke at the environment
>>>>>> (warning if anyone does try this and the bug hits it can render your
>>>>>> u-boot environment invalid).
>>>>>>
>>>>>> cat flash/fw_env_test.sh
>>>>>> #!/bin/sh
>>>>>>
>>>>>> generate_fw_env_config()
>>>>>> {
>>>>>>    cat /proc/mtd | sed 's/[:"]//g' | while read dev size erasesize
>>>>>> name ; do
>>>>>>       echo "$dev $size $erasesize $name"
>>>>>>       [ "$name" = "u-boot-env" ] && echo "/dev/$dev 0x0000 0x2000
>>>>>> $erasesize" >/flash/fw_env.config
>>>>>>    done
>>>>>> }
>>>>>>
>>>>>> cycles=10
>>>>>> [ $# -ge 1 ] && cycles=$1
>>>>>>
>>>>>> generate_fw_env_config
>>>>>>
>>>>>> fw_printenv -c /flash/fw_env.config
>>>>>>
>>>>>> dmesg -c >/dev/null
>>>>>> x=0
>>>>>> while [ $x -lt $cycles ]; do
>>>>>>      fw_printenv -c /flash/fw_env.config >/dev/null || break
>>>>>>      fw_setenv -c /flash/fw_env.config foo $RANDOM || break;
>>>>>>      dmesg -c | grep -q fsl_espi && break;
>>>>>>      let x=x+1
>>>>>> done
>>>>>>
>>>>>> echo "Ran $x cycles"
>>>>> I've also now seen the RX FIFO not empty error on the T2080RDB
>>>>>
>>>>> fsl_espi ffe110000.spi: Transfer done but SPIE_DON isn't set!
>>>>> fsl_espi ffe110000.spi: Transfer done but SPIE_DON isn't set!
>>>>> fsl_espi ffe110000.spi: Transfer done but SPIE_DON isn't set!
>>>>> fsl_espi ffe110000.spi: Transfer done but SPIE_DON isn't set!
>>>>> fsl_espi ffe110000.spi: Transfer done but rx/tx fifo's aren't empty!
>>>>> fsl_espi ffe110000.spi: SPIE_RXCNT = 1, SPIE_TXCNT = 32
>>>>>
>>>>> With my current workaround of emptying the RX FIFO. It seems
>>>>> survivable. Interestingly it only ever seems to be 1 extra byte in the
>>>>> RX FIFO and it seems to be after either a READ_SR or a READ_FSR.
>>>>>
>>>>> fsl_espi ffe110000.spi: tx 70
>>>>> fsl_espi ffe110000.spi: rx 03
>>>>> fsl_espi ffe110000.spi: Extra RX 00
>>>>> fsl_espi ffe110000.spi: Transfer done but SPIE_DON isn't set!
>>>>> fsl_espi ffe110000.spi: Transfer done but rx/tx fifo's aren't empty!
>>>>> fsl_espi ffe110000.spi: SPIE_RXCNT = 1, SPIE_TXCNT = 32
>>>>> fsl_espi ffe110000.spi: tx 05
>>>>> fsl_espi ffe110000.spi: rx 00
>>>>> fsl_espi ffe110000.spi: Extra RX 03
>>>>> fsl_espi ffe110000.spi: Transfer done but SPIE_DON isn't set!
>>>>> fsl_espi ffe110000.spi: Transfer done but rx/tx fifo's aren't empty!
>>>>> fsl_espi ffe110000.spi: SPIE_RXCNT = 1, SPIE_TXCNT = 32
>>>>> fsl_espi ffe110000.spi: tx 05
>>>>> fsl_espi ffe110000.spi: rx 00
>>>>> fsl_espi ffe110000.spi: Extra RX 03
>>>>>
>>>>>  From all the Micron SPI-NOR datasheets I've got access to it is
>>>>> possible to continually read the SR/FSR. But I've no idea why it
>>>>> happens some times and not others.
>>>> So I think I've got a reproduction and I think I've bisected the problem
>>>> to commit 3282a3da25bd ("powerpc/64: Implement soft interrupt replay in
>>>> C"). My day is just finishing now so I haven't applied too much scrutiny
>>>> to this result. Given the various rabbit holes I've been down on this
>>>> issue already I'd take this information with a good degree of skepticism.
>>>>
>>> OK, so an easy test should be to re-test with a 5.4 kernel.
>>> It doesn't have yet the change you're referring to, and the fsl-espi driver
>>> is basically the same as in 5.7 (just two small changes in 5.7).
>> There's 6cc0c16d82f88 and maybe also other interrupt related patches
>> around this time that could affect book E, so it's good if that exact
>> patch is confirmed.
> 
> My confirmation is basically that I can induce the issue in a 5.4 kernel 
> by cherry-picking 3282a3da25bd. I'm also able to "fix" the issue in 
> 5.9-rc2 by reverting that one commit.
> 
> I both cases it's not exactly a clean cherry-pick/revert so I also 
> confirmed the bisection result by building at 3282a3da25bd (which sees 
> the issue) and the commit just before (which does not).

Thanks for testing, that confirms it well.

[snip patch]

> I still saw the issue with this change applied. PPC_IRQ_SOFT_MASK_DEBUG 
> didn't report anything (either with or without the change above).

Okay, it was a bit of a shot in the dark. I still can't see what
else has changed.

What would cause this, a lost interrupt? A spurious interrupt? Or
higher interrupt latency?

I don't think the patch should cause significantly worse latency,
(it's supposed to be a bit better if anything because it doesn't set
up the full interrupt frame). But it's possible.

Thanks,
Nick