linux-kernel - Re: Question regarding RT patches for ARM

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Message-ID: <CAGgoGu6d36V6pcJixWCFEaGYV7osCjug0jW5F0PqSpTXXWzcpw@mail.gmail.com>
Date:   Thu, 18 May 2017 10:45:53 +0200
From:   Fawad Lateef <fawadlateef@...il.com>
To:     Eric Nelson <eric@...int.com>
Cc:     GuJiangfei <qiledexin@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: Question regarding RT patches for ARM

Hi Eric,


On 17 May 2017 at 16:45, Eric Nelson <eric@...int.com> wrote:
> Hi Fawad,
>
> On 05/17/2017 06:40 AM, Fawad Lateef wrote:
>>
>> On 15 May 2017 at 16:20, Fawad Lateef <fawadlateef@...il.com> wrote:
>>>
>>> Hi Eric,
>>> On 15 May 2017 at 16:12, Eric Nelson <eric@...int.com> wrote:
>>>>
>>>> Hi Fawad,
>>>>
>>>>> 发自网易邮箱大师
>>>>> On 05/15/2017 20:44, Fawad Lateef wrote:
>>>>>
>>>>> Hi All,
>>>>>
>>>>> I am working on custom i.MX6 quad hardware and using RT patches for
>>>>> almost latest stable kernel 4.9 and facing some weird system stall OR
>>>>> 'unhandled page fault - exceptions'.
>>>>>
>>>>
>>>> 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
>>>>
>>>
>>> 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).
>

Yes SDMA can be used for many devices but in our case its only set to
use for NOR (to confirm I also checked sdma interrupts in system and
they just 21 or so which happened during boot time).

>> 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 believe Alison Chaiken mentioned using them with 4.9 kernels:
> http://elinux.org/images/4/42/IRQs-_the_Hard%2C_the_Soft%2C_the_Threaded_and_the_Preemptible.pdf
> https://www.youtube.com/watch?v=-pehAzaP1eg&feature=youtu.be&list=PLbzoR-pLrL6pRFP6SOywVJWdEHlmQE51q
>

Thanks for the video/link. Seems like very informative. Will check it soon.

> Regards,
>
>
> Eric

Regards,

Fawad Lateef