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

[Vladimir Murzin <vladimir.murzin@arm.com>]

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:
>>
>> I've been running Linux on Cortex-R cores with downstream patches for
>> several years already. There are few reasons why we have not got any
>> real platform supporting Cortex-R cores so far:
>> 1) lack of interest
>> 2) lack of easily available platforms
>> 3) missing Kconfig bits
>>
>> During these years I've been receiving questions (mostly in private)
>> about running Linux with Cortex-R cores. Use cases vary, but mostly
>> fall under "we know Linux and do not want yet another RTOS", also
>> people not always care about real-time features of R-class cores and
>> see it as an upgrade from M-class cores.
>>
>> Sometime ago MPS3 platform got support for FPGA image [1] with
>> Cortex-R52 cores where Linux can live comfortably.
>>
>> This patchset addresses #3 and brings support for MPS3 platform
>> featuring Cortex-R52
> 
> The patches look ok to me, if we want to support Cortex-R, this
> is clearly how it should be done.

Thanks!

> 
> 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...

> 
> 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.

> 
> 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"

Cheers
Vladimir

> 
>          Arnd


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