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

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Message-ID: <c0fc9f9b-ae0b-66d3-71c7-e2b98f6900e0@nelint.com>
Date:   Wed, 17 May 2017 07:45:39 -0700
From:   Eric Nelson <eric@...int.com>
To:     Fawad Lateef <fawadlateef@...il.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 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).

> 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

Regards,


Eric