Imprecise External Abort on MX6/UART

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Imprecise External Abort on MX6/UART

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andrerenaud2
Contributor II

Hello,

I am working with an iMX6Q system that is exhibiting a crash when using the serial ports.We have /dev/ttymxc2 configured as an RS485 UART, and are seeing an 'imprecise external abort' after some time of use (panic listed below).
We are able to replicate this both on the custom kernel we're using, as well as on the 5.3.x+fslc image from https://github.com/Freescale/linux-fslc


To replicate it we have the mx6 hooked up to a PC, with each end sending short 3-4 character messages every second. The fault kicks in after about 15-30 minutes. This seems similar to the fault described here: https://lkml.org/lkml/2019/11/11/588. We have tried shutting down DMA and various performance/cpuidle systems, but that doesn't seem to have any impact.


Does anyone have any thoughts on how to solve this?


Regards,

Andre


[ 5047.074427] Unhandled fault: imprecise external abort (0x1406) at 0xb6e00f78
[ 5047.081498] pgd = c0004000
[ 5047.084213] [b6e00f78] *pgd=00000000
[ 5047.087813] Internal error: : 1406 [#1] SMP ARM
[ 5047.092348] Modules linked in:
[ 5047.095429] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.8.0+ #19
[ 5047.101440] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 5047.107974] task: ef0ecd00 task.stack: ef158000
[ 5047.112521] PC is at arch_cpu_idle+0x48/0x4c
[ 5047.116799] LR is at arch_cpu_idle+0x44/0x4c
[ 5047.121077] pc : [<c0108c70>]    lr : [<c0108c6c>]    psr: 60070013
[ 5047.121077] sp : ef159f98  ip : ef159fa8  fp : ef159fa4
[ 5047.132560] r10: 00000000  r9 : 00000002  r8 : c0d025dc
[ 5047.137791] r7 : c0d95448  r6 : ef158000  r5 : c0d02648  r4 : ef158000
[ 5047.144324] r3 : c011a140  r2 : 005bc18a  r1 : ef7ae3c0  r0 : 00000000
[ 5047.150858] Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
[ 5047.157998] Control: 10c5387d  Table: 3dd9804a  DAC: 00000051
[ 5047.163748] Process swapper/1 (pid: 0, stack limit = 0xef158210)
[ 5047.169759] Stack: (0xef159f98 to 0xef15a000)
[ 5047.174124] 9f80:                                                       ef159fb4 ef159fa8
[ 5047.182310] 9fa0: c0170b54 c0108c34 ef159fdc ef159fb8 c0170da4 c0170b30 c0a8fb48 c0d8b845
[ 5047.190496] 9fc0: c0d8c48c c0d025dc 10c0387d c0d95448 ef159ff4 ef159fe0 c010e6cc c0170b6c
[ 5047.198682] 9fe0: 3f0fc06a 00000051 00000000 ef159ff8 101018cc c010e580 edddf4eb ffeebffd
[ 5047.206887] [<c0108c70>] (arch_cpu_idle) from [<c0170b54>] (default_idle_call+0x30/0x3c)
[ 5047.214993] [<c0170b54>] (default_idle_call) from [<c0170da4>] (cpu_startup_entry+0x244/0x298)
[ 5047.223619] [<c0170da4>] (cpu_startup_entry) from [<c010e6cc>] (secondary_start_kernel+0x158/0x164)
[ 5047.232677] [<c010e6cc>] (secondary_start_kernel) from [<101018cc>] (0x101018cc)
[ 5047.240083] Code: e34c30d0 e5933014 e12fff33 f1080080 (e89da800)
[ 5047.246190] ---[ end trace 853e028df8c9b7cd ]---
[ 5047.250814] Kernel panic - not syncing: Attempted to kill the idle task!
[ 5047.257528] CPU2: stopping
[ 5047.260250] CPU: 2 PID: 0 Comm: swapper/2 Tainted: G      D         4.8.0+ #19
[ 5047.267476] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 5047.274022] [<c0110cc4>] (unwind_backtrace) from [<c010c9d0>] (show_stack+0x20/0x24)
[ 5047.281783] [<c010c9d0>] (show_stack) from [<c04939c8>] (dump_stack+0x90/0xa4)
[ 5047.289019] [<c04939c8>] (dump_stack) from [<c010ebe8>] (handle_IPI+0x2a4/0x2c4)
[ 5047.296426] [<c010ebe8>] (handle_IPI) from [<c01014dc>] (gic_handle_irq+0x80/0x84)
[ 5047.304013] [<c01014dc>] (gic_handle_irq) from [<c080c8cc>] (__irq_svc+0x6c/0x90)
[ 5047.311500] Exception stack(0xef15bf48 to 0xef15bf90)
[ 5047.316561] bf40:                   00000000 ef7bd3c0 00729232 c011a140 ef15a000 c0d02648
[ 5047.324747] bf60: ef15a000 c0d95448 c0d025dc 00000004 00000000 ef15bfa4 ef15bfa8 ef15bf98
[ 5047.332930] bf80: c0108c6c c0108c70 60000013 ffffffff
[ 5047.337999] [<c080c8cc>] (__irq_svc) from [<c0108c70>] (arch_cpu_idle+0x48/0x4c)
[ 5047.345410] [<c0108c70>] (arch_cpu_idle) from [<c0170b54>] (default_idle_call+0x30/0x3c)
[ 5047.353514] [<c0170b54>] (default_idle_call) from [<c0170da4>] (cpu_startup_entry+0x244/0x298)
[ 5047.362137] [<c0170da4>] (cpu_startup_entry) from [<c010e6cc>] (secondary_start_kernel+0x158/0x164)
[ 5047.371191] [<c010e6cc>] (secondary_start_kernel) from [<101018cc>] (0x101018cc)
[ 5047.378593] CPU3: stopping
[ 5047.381314] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G      D         4.8.0+ #19
[ 5047.388540] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 5047.395085] [<c0110cc4>] (unwind_backtrace) from [<c010c9d0>] (show_stack+0x20/0x24)
[ 5047.402841] [<c010c9d0>] (show_stack) from [<c04939c8>] (dump_stack+0x90/0xa4)
[ 5047.410073] [<c04939c8>] (dump_stack) from [<c010ebe8>] (handle_IPI+0x2a4/0x2c4)
[ 5047.417479] [<c010ebe8>] (handle_IPI) from [<c01014dc>] (gic_handle_irq+0x80/0x84)
[ 5047.425060] [<c01014dc>] (gic_handle_irq) from [<c080c8cc>] (__irq_svc+0x6c/0x90)
[ 5047.432546] Exception stack(0xef15df48 to 0xef15df90)
[ 5047.437606] df40:                   00000000 ef7cc3c0 00512f92 c011a140 ef15c000 c0d02648
[ 5047.445792] df60: ef15c000 c0d95448 c0d025dc 00000008 00000000 ef15dfa4 ef15dfa8 ef15df98
[ 5047.453974] df80: c0108c6c c0108c70 600d0013 ffffffff
[ 5047.459041] [<c080c8cc>] (__irq_svc) from [<c0108c70>] (arch_cpu_idle+0x48/0x4c)
[ 5047.466452] [<c0108c70>] (arch_cpu_idle) from [<c0170b54>] (default_idle_call+0x30/0x3c)
[ 5047.474555] [<c0170b54>] (default_idle_call) from [<c0170da4>] (cpu_startup_entry+0x244/0x298)
[ 5047.483179] [<c0170da4>] (cpu_startup_entry) from [<c010e6cc>] (secondary_start_kernel+0x158/0x164)
[ 5047.492234] [<c010e6cc>] (secondary_start_kernel) from [<101018cc>] (0x101018cc)
[ 5047.499635] CPU0: stopping
[ 5047.502356] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G      D         4.8.0+ #19
[ 5047.509582] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[ 5047.516126] [<c0110cc4>] (unwind_backtrace) from [<c010c9d0>] (show_stack+0x20/0x24)
[ 5047.523883] [<c010c9d0>] (show_stack) from [<c04939c8>] (dump_stack+0x90/0xa4)
[ 5047.531116] [<c04939c8>] (dump_stack) from [<c010ebe8>] (handle_IPI+0x2a4/0x2c4)
[ 5047.538521] [<c010ebe8>] (handle_IPI) from [<c01014dc>] (gic_handle_irq+0x80/0x84)
[ 5047.546102] [<c01014dc>] (gic_handle_irq) from [<c080c8cc>] (__irq_svc+0x6c/0x90)
[ 5047.553588] Exception stack(0xc0d01d78 to 0xc0d01dc0)
[ 5047.558645] 1d60:                                                       ee4dfae8 20070113
[ 5047.566831] 1d80: 00000730 000049db ee4dfa80 ef3d9de0 ee4dfae8 20070113 00000020 00000000
[ 5047.575016] 1da0: c0d0799c c0d01dd4 c0d01dd8 c0d01dc8 c05fdd00 c080c26c 60070113 ffffffff
[ 5047.583205] [<c080c8cc>] (__irq_svc) from [<c080c26c>] (_raw_spin_unlock_irqrestore+0x30/0x34)
[ 5047.591839] [<c080c26c>] (_raw_spin_unlock_irqrestore) from [<c05fdd00>] (sdhci_tasklet_finish+0xfc/0x234)
[ 5047.601507] [<c05fdd00>] (sdhci_tasklet_finish) from [<c012dfe8>] (tasklet_action+0x68/0xf8)
[ 5047.609955] [<c012dfe8>] (tasklet_action) from [<c0101630>] (__do_softirq+0x150/0x34c)
[ 5047.617892] [<c0101630>] (__do_softirq) from [<c012d9e0>] (irq_exit+0xc8/0x128)
[ 5047.625218] [<c012d9e0>] (irq_exit) from [<c0181338>] (__handle_domain_irq+0x70/0xc4)
[ 5047.633060] [<c0181338>] (__handle_domain_irq) from [<c01014a4>] (gic_handle_irq+0x48/0x84)
[ 5047.641421] [<c01014a4>] (gic_handle_irq) from [<c080c8cc>] (__irq_svc+0x6c/0x90)
[ 5047.648907] Exception stack(0xc0d01f08 to 0xc0d01f50)
[ 5047.653965] 1f00:                   00000000 ef79f3c0 00449df4 c011a140 c0d00000 c0d02648
[ 5047.662151] 1f20: c0d00000 c0d02540 c0d025dc 00000001 ef7db300 c0d01f64 c0d01f68 c0d01f58
[ 5047.670333] 1f40: c0108c6c c0108c70 60070013 ffffffff
[ 5047.675399] [<c080c8cc>] (__irq_svc) from [<c0108c70>] (arch_cpu_idle+0x48/0x4c)
[ 5047.682809] [<c0108c70>] (arch_cpu_idle) from [<c0170b54>] (default_idle_call+0x30/0x3c)
[ 5047.690911] [<c0170b54>] (default_idle_call) from [<c0170da4>] (cpu_startup_entry+0x244/0x298)
[ 5047.699533] [<c0170da4>] (cpu_startup_entry) from [<c0806eb8>] (rest_init+0x84/0x88)
[ 5047.707292] [<c0806eb8>] (rest_init) from [<c0c00d34>] (start_kernel+0x390/0x39c)
[ 5047.714786] ---[ end Kernel panic - not syncing: Attempted to kill the idle task!

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andrerenaud2
Contributor II

Hi Igor,

We have recently updated the DDR timings, and that did not seem to make any difference.

We've also been able to replicate the fault using the linux-imx from 
https://source.codeaurora.org/external/imx/linux-imx/tree/?h=imx_4.19.35_1.1.0

We're able to replicate the fault on the Wandboard. To replicate it on the Wandboard we soldered wires onto the uart2 pins, configured it as RS485 in device tree and then read/wrote data on the UART in a tight loop. It crashed after about 2 minutes.

Regards,

Andre

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Andre

wandboard is not supported by nxp, please try to reproduce issue on

nxp reference board.i.MX 6Quad SABRE Development Board | NXP 


Best regards
igor

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andrerenaud2
Contributor II

Hello Igor,

We were not able to replicate the issue on that board. However we have found the root cause of the issue. It was a timing issue in the RX disable feature that happens when using the SER_RS485_RX_DURING_TX flag for RS485. This has been previously discussed, and a patch proposed here Re: imx: Race when disabling RX in IMX.6 UART in half duplex — ARM, OMAP, Xscale Linux Kernel . 

Once we applied that patch, the issue was resolved.

Regards,

Andre

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igorpadykov
NXP TechSupport
NXP TechSupport

Hi Andre

may be useful to test memory with ddr test

i.MX6/7 DDR Stress Test Tool V3.00 

and update image with new ddr calibration coefficients found from test

Also recommended to try official nxp linux from source.codeaurora.org/external/imx/linux-imx

repository:

linux-imx - i.MX Linux kernel 

Best regards
igor
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