Re: [RFC PATCH 0/3] ARM: Support Cortex-R platform(s)

From: Vladimir Murzin <vladimir.murzin@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Ayan Kumar Halder <ayan.kumar.halder@xilinx.com>,
	Stefano Stabellini <stefanos@xilinx.com>
Subject: Re: [RFC PATCH 0/3] ARM: Support Cortex-R platform(s)
Date: Fri, 1 Jul 2022 15:38:21 +0100	[thread overview]
Message-ID: <0a12aa00-f3b5-bc54-b756-38aa06a496fd@arm.com> (raw)
In-Reply-To: <CAK8P3a3w7aUVWi4DG+P1gfWDOoHq=a1ZshDZ41=cp_sb2ErjYQ@mail.gmail.com>

On 7/1/22 15:18, Arnd Bergmann wrote:
> On Fri, Jul 1, 2022 at 11:39 AM Vladimir Murzin <vladimir.murzin@arm.com> wrote:
>> On 6/30/22 22:17, Arnd Bergmann wrote:
>>> On Thu, Jun 30, 2022 at 10:36 AM Vladimir Murzin
>>> <vladimir.murzin@arm.com> wrote:
>>> My main concern is the same as the one we discussed before:
>>> are there actually use cases for which running Linux con Cortex-R
>>> is the right thing to do?
>>
>> Unfortunately, people who have been wondering how to run Linux on
>> Cortex-R are not keen to uncover their use cases it details. Maybe
>> that for quick prototyping or just curiosity...
> 
> Do you know which SoCs they are using? That may give a hint.

No.

> 
>>> While it's clearly an awesome hack that this actually works, I don't
>>> really want to encourage developers to ship products with Linux
>>> on Cortex-R unless there is at least one sensible use case for it.
>>
>> It could be that already happening and we are not aware because
>> area of application might not be visible or broad.
> 
> I'm not too worried about non-mainline products here.
> 
>>> The Cortex-M support is still holding up for the moment, but I
>>> don't think there have been any new deployments in years
>>> (there are a few new hobbyist projects like the imxrt and the
>>> stm32 art pi), and I expect that we will want to completely remove
>>> nommu support at some point.
>>
>> At least for M-class I was told about commercial application (yet in
>> low volume) - the reason why Linux was exactly "we know Linux and
>> do not want yet another RTOS"
> 
> I think that was a common view until a few years ago, but has gotten
> much less common recently. In Linaro, we had multiple developers
> working on Cortex-M, in particular getting ELF-FDPIC support
> working properly. Emcraft had its entire business built around this
> seems to have completely stopped: the software on their website
> has never been updated to use FDPIC or kernels newer than
> linux-4.5.
> 
> Are you aware of anyone going into production recently, and
> based on a more modern kernel?

I'm not at the level where I can observe production story :( Case I
mentioned was around 4.13~4.20

Cheers
Vladimir

> 
>        Arnd

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