Re: Question regarding RT patches for ARM

From	Fawad Lateef <fawadlateef@gmail.com>
Newsgroups	linux.kernel
Subject	Re: Question regarding RT patches for ARM
Date	2017-05-18 13:10 +0200
Message-ID	<tIrtH-1zL-91@gated-at.bofh.it> (permalink)
References	(3 earlier) <tHp0R-O3-13@gated-at.bofh.it> <tHpay-Ra-27@gated-at.bofh.it> <tI7uV-3HE-1@gated-at.bofh.it> <tI8r1-4kw-39@gated-at.bofh.it> <tI9Gq-5g6-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

Hi Sebastian,


On 17 May 2017 at 18:02, Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
> On 2017-05-17 07:45:39 [-0700], Eric Nelson wrote:
>> Hi Fawad,
> Hi Fawad,
>
>> On 05/17/2017 06:40 AM, Fawad Lateef wrote:
>> > > > I'm not sure about the unhandled page fault, but the stalls may be
>> > > > because of the SDMA driver.
>> > > >
>> > > > See this patch in the Freescale/NXP community for kernel 4.1:
>> > > > https://github.com/Freescale/meta-freescale/blob/master/recipes-kernel/linux/linux-fslc-imx-rt/0003-Work-around-CPU-stalls-in-the-imx-sdma-driver.patch
>
> That is something I see for the first time. The description says that it
> leads to this stall but it fails to explain _how_ it got there.
>
>> > > Thanks for the patch link. I will give it a try.
>> >
>> > Talked to hardware manufacturer and they applied the patch.
>> >
>> > Still that SDMA is only used for NOR flash and only u-boot and its
>> > environment are stored in nor flash. So not sure if that is going to
>> > help in any case.
>> >
>>
>> SDMA is used for much more than NOR flash (SSI, USB, and sometimes
>> UARTs).
>>
>> > So I would really like few more suggestions OR confirmations about ARM
>> > (cortex-A9 based imx6) (preemept)-RT support/patches are stable and
>> > can be used for final products.
>> >
>>
>> I don't have any experience with the RT patches on 4.9 or later
>> kernels, but do know that they're being used on i.MX6 with the
>> vendor kernels (3.10.x, 4.1.x).
>
> I just looked into a few boot logs and it seems the Phyflex board (imx6
> quad) bootet v4.9.27-rt18, run cyclictest including some tests and
> nothing produced this "unhandled page fault" you mention here. This
> includes the previous RT version in the v4.9 line.
>

Thanks, seems like RT patches are quite stable for ARM then.

> Of this "page fault" happens on boot, it has to do something without
> your .config + hw combination. If it happens at rune-time it is probably
> triggered by a driver or an application is triggering this.
>

Yes, this happens at run-time and not always. Sometimes hardware just
hangs/stalls.

As now RT is widely used on ARM so to me seems like it something
related to hardware design/setting OR application.

Another question: Is RT user-space application can make kernel/system
crash? As to me kernel should kill the app but let itself running
_but_ not sure in the case of RT patched kernel.

>> Regards,
>>
>>
>> Eric
>
> Sebastian

Thanks,

Fawad Lateef

Thread

Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-15 14:50 +0200
  Re: Question regarding RT patches for ARM Richard Weinberger <richard.weinberger@gmail.com> - 2017-05-15 15:10 +0200
  Re: Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-15 15:20 +0200
    Re: Question regarding RT patches for ARM Sebastian Andrzej Siewior <sebastian.siewior@linutronix.de> - 2017-05-15 15:50 +0200
      Re: Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-15 16:10 +0200
    Re: Question regarding RT patches for ARM Eric Nelson <eric@nelint.com> - 2017-05-15 16:20 +0200
      Re: Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-15 16:30 +0200
        Re: Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-17 15:50 +0200
          Re: Question regarding RT patches for ARM Eric Nelson <eric@nelint.com> - 2017-05-17 16:50 +0200
            Re: Question regarding RT patches for ARM Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-05-17 18:10 +0200
              Re: Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-18 13:10 +0200
                Re: Question regarding RT patches for ARM Sebastian Andrzej Siewior <bigeasy@linutronix.de> - 2017-05-18 22:20 +0200
            Re: Question regarding RT patches for ARM Fawad Lateef <fawadlateef@gmail.com> - 2017-05-18 10:50 +0200

csiph-web