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

[Arnd Bergmann]

On Fri, Jul 1, 2022 at 11:39 AM Vladimir Murzin <vladimir.murzin at 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 at 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.

> > 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?

       Arnd