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

[Arnd Bergmann <arnd@arndb.de>]

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.

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?

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.

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.

         Arnd

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