Re: [PATCH v2] i2c: omap: Fix standard mode false ACK readings

Ing. Josua Mayer
2025-02-02T22:42:29Z

Am 06.11.24 um 16:09 schrieb H. Nikolaus Schaller:
>
>> Am 06.11.2024 um 13:16 schrieb H. Nikolaus Schaller <hns@goldelico.com>:
>>
>>
>>
>>> Am 06.11.2024 um 10:23 schrieb Andreas Kemnade <andreas@kemnade.info>:
>>>
>>> Am Wed, 11 Sep 2024 11:40:04 +0200
>>> schrieb "H. Nikolaus Schaller" <hns@goldelico.com>:
>>>
>>>> Hi,
>>>>
>>>>> Am 28.04.2023 um 20:30 schrieb Reid Tonking <reidt@ti.com>:
>>>>>
>>>>> On 10:43-20230428, Tony Lindgren wrote:
>>>>>> * Raghavendra, Vignesh <vigneshr@ti.com> [230427 13:18]:
>>>>>>> On 4/27/2023 1:19 AM, Reid Tonking wrote:
>>>>>>>> Using standard mode, rare false ACK responses were appearing with
>>>>>>>> i2cdetect tool. This was happening due to NACK interrupt
>>>>>>>> triggering ISR thread before register access interrupt was
>>>>>>>> ready. Removing the NACK interrupt's ability to trigger ISR
>>>>>>>> thread lets register access ready interrupt do this instead.
>>>>>> So is it safe to leave NACK interrupt unhandled until we get the
>>>>>> next interrupt, does the ARDY always trigger after hitting this?
>>>>>>
>>>>>> Regards,
>>>>>>
>>>>>> Tony
>>>>> Yep, the ARDY always gets set after a new command when register
>>>>> access is ready so there's no need for NACK interrupt to control
>>>>> this.
>>>> I have tested one GTA04A5 board where this patch breaks boot on
>>>> v4.19.283 or v6.11-rc7 (where it was inherited from some earlier -rc
>>>> series).
>>>>
>>>> The device is either stuck with no signs of activity or reports RCU
>>>> stalls after a 20 second pause.
>>>>
>>> Reproduced some problem here:
>>> i2cset 1 0x69 0x14 0xb6 (reset command for gyro BMG160)
>>> [ 736.136108] omap_i2c 48072000.i2c: addr: 0x0069, len: 2, flags: 0x0,
>>> stop: 1
>>> [ 736.136322] omap_i2c 48072000.i2c: IRQ (ISR = 0x0010)
>>> either with this patch applied:
>>> ... system mostly hangs, i2cset does not return.
>>> with it reverted:
>>> ... most times I see after this:
>>> [ 736.136505] omap_i2c 48072000.i2c: IRQ (ISR = 0x0002)
>>> and i2cset says:
>>> i2cset: write failed: Remote I/O error
>>>
>>> ... sometimes:
>>> omap_i2c 48072000.i2c: IRQ (ISR = 0x0004)
>>> and i2cset is successful.
>>>
>>> Other register writes seem to work reliably, just the reset command.
>>> I had tested with bmg driver disabled earlier,
>>> so it did not come to light.
>> Indeed, I can confirm with your sequence (and bmg driver voluntarily
>> disabled so that the effect just comes from the i2c bus & client chip).
>>
>> 1. echo blacklist bmg160_i2c >/etc/modprobe.d/test.conf
>> 2. reboot & login:
>> 3.
>>
>> Last login: Wed Nov 6 11:24:37 UTC 2024 on ttyO2
>> root@letux:~# dmesg|fgrep bmg
>> root@letux:~# i2cset -y 1 0x69 0x14 0xb6
>> root@letux:~# i2cset -y 1 0x69 0x14 0xb6
>> root@letux:~# i2cset -y 1 0x69 0x14 0xb6
>> root@letux:~# i2cset -y 1 0x69 0x14 0xb6
>> --- hangs for some seconds ---
>> [ 109.664245] rcu: INFO: rcu_preempt self-detected stall on CPU
>> [ 109.670318] rcu: 0-...!: (2100 ticks this GP) idle=7e74/1/0x40000004 softirq=9248/9248 fqs=0
>> [ 109.679260] rcu: (t=2100 jiffies g=11389 q=33 ncpus=1)
>> [ 109.684753] rcu: rcu_preempt kthread timer wakeup didn't happen for 2099 jiffies! g11389 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
>> [ 109.696685] rcu: Possible timer handling issue on cpu=0 timer-softirq=4004
>> [ 109.704010] rcu: rcu_preempt kthread starved for 2100 jiffies! g11389 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0
>> [ 109.714935] rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
>> [ 109.724517] rcu: RCU grace-period kthread stack dump:
>> [ 109.729797] task:rcu_preempt state:I stack:0 pid:15 tgid:15 ppid:2 flags:0x00000000
>> [ 109.739593] Call trace:
>> [ 109.739593] __schedule from schedule+0x3c/0x64
>> [ 109.747039] schedule from schedule_timeout+0xa8/0xd4
>> [ 109.752349] schedule_timeout from rcu_gp_fqs_loop+0x148/0x370
>> [ 109.758514] rcu_gp_fqs_loop from rcu_gp_kthread+0xec/0x124
>> [ 109.764373] rcu_gp_kthread from kthread+0xfc/0x108
>> [ 109.769500] kthread from ret_from_fork+0x14/0x28
>> [ 109.774444] Exception stack(0xf0041fb0 to 0xf0041ff8)
>> [ 109.779754] 1fa0: 00000000 00000000 00000000 00000000
>> [ 109.788330] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> [ 109.796905] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
>> [ 109.803863] CPU: 0 UID: 0 PID: 3210 Comm: loginwindow Not tainted 6.12.0-rc6-letux+ #169
>> [ 109.803894] Hardware name: Generic OMAP36xx (Flattened Device Tree)
>> [ 109.803894] PC is at handle_softirqs+0x84/0x300
>> [ 109.803924] LR is at handle_softirqs+0x54/0x300
>> [ 109.803955] pc : [<c0133c3c>] lr : [<c0133c0c>] psr: 60070113
>> [ 109.803955] sp : f0001fa0 ip : 844ce392 fp : c0f02080
>> [ 109.803985] r10: f0651be0 r9 : c1008d28 r8 : f0651be8
>> [ 109.803985] r7 : c0f02d40 r6 : 00000200 r5 : c0e91600 r4 : c0e91600
>> [ 109.803985] r3 : 2e70d000 r2 : 00000000 r1 : c0e91600 r0 : c23cad00
>> [ 109.804016] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none
>> [ 109.804016] Control: 10c5387d Table: 82b70019 DAC: 00000051
>> [ 109.804016] Call trace:
>> [ 109.804046] handle_softirqs from __irq_exit_rcu+0x6c/0xb4
>> [ 109.804077] __irq_exit_rcu from irq_exit+0x8/0x10
>> [ 109.804077] irq_exit from call_with_stack+0x18/0x20
>> [ 109.804138] call_with_stack from __irq_svc+0x98/0xcc
>> [ 109.804138] Exception stack(0xf0651b60 to 0xf0651ba8)
>> [ 109.804168] 1b60: c2c8f300 f0651ce0 c085aec0 c2c8f300 00000000 00000019 00000000 00000000
>> [ 109.804168] 1b80: f0651be8 00000000 f0651be0 00000000 ffffffff f0651bb0 c02ba850 c085aec0
>> [ 109.804199] 1ba0: a0070113 ffffffff
>> [ 109.804199] __irq_svc from sock_poll+0x0/0xbc
>> [ 109.804229] sock_poll from do_sys_poll+0x2a8/0x460
>> [ 109.804260] do_sys_poll from sys_poll+0x74/0xe8
>> [ 109.804290] sys_poll from ret_fast_syscall+0x0/0x54
>> [ 109.804290] Exception stack(0xf0651fa8 to 0xf0651ff0)
>> [ 109.804321] 1fa0: 0000409b 00162f90 beeb07cc 00000001 ffffffff 00000000
>> [ 109.804321] 1fc0: 0000409b 00162f90 b61c3080 000000a8 00000000 00162f9c 00163f90 beeb0874
>> [ 109.804351] 1fe0: 000000a8 beeb07a8 b6a83bd7 b6a057e6
>>
>>
> After reverting this patch, I get some sporadic write errors but no kernel crashes:
>
> root@letux:~# while true; do i2cset -y 1 0x69 0x14 0xb6 && echo good; done
> Error: Write failed
> good
> Error: Write failed
> good
> good
> good
> good
> Error: Write failed
> good
> Error: Write failed
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> good
> Error: Write failed
> good
> ^C
> root@letux:~#
>
> So there are chips (like BMG160) which might block the SDA/SCL lines in a
> strange way where the patched i2c driver fails instead of timing out and
> reporting an error.
>
> Therefore, I'd suggest to revert it or find a proper fix.

I just came across this in 6.12.9, as well as 5.4.243 which pulled in
this patch.
Affected is omap3-gta04a5.dts which worked perfectly fine at 5.4.242.

Please revert until a solution has been found.