Re: [PATCH 1/6] ARM: stm32: prepare stm32 family to welcome armv7 architecture

[Ludovic BARRE]

On 12/11/2017 02:40 PM, Arnd Bergmann wrote:
> On Mon, Dec 11, 2017 at 11:25 AM, Linus Walleij
> <linus.walleij@xxxxxxxxxx> wrote:
> > On Fri, Dec 8, 2017 at 3:11 PM, Ludovic Barre <ludovic.Barre@xxxxxx> wrote:
> >
> > > From: Ludovic Barre <ludovic.barre@xxxxxx>
> > >
> > > This patch prepares the STM32 machine for the integration of Cortex-A
> > > based microprocessor (MPU), on top of the existing Cortex-M
> > > microcontroller family (MCU). Since both MCUs and MPUs are sharing
> > > common hardware blocks we can keep using ARCH_STM32 flag for most of
> > > them. If a hardware block is specific to one family we can use either
> > > ARCH_STM32_MCU or ARCH_STM32_MPU flag.
> > >
> > > Signed-off-by: Ludovic Barre <ludovic.barre@xxxxxx>
>
> To what degree do we need to treat them as separate families
> at all then? I wonder if the MCU/MPU distinction is always that
> clear along the Cortex-M/Cortex-A separation, especially if
> we ever get to a chip that has both types of cores. What
> exactly would we miss if we do away with the ARCH_STM32_MCU
> symbol here?
This patch series extends the existing STM32 microcontrollers (MCUs)
family to microprocessors (MPUs). Now, ARCH_STM32 groups STM32 chips 
with Cortex-M or Cortex-A cores. But each core has different 
infrastructure mpu vs mmu; nvic vs gic; systick vs arch_timer ...
So, ARCH_STM32_MCU/ARCH_STM32_MPU allow to define these specific blocks.

br
Ludo
> > So yesterdays application processors are todays MCU processors.
> >
> > I said this on a lecture for control systems a while back and
> > stated it as a reason I think RTOSes are not really seeing a bright
> > future compared to Linux.
> >
> > It happened quicker than I thought though, interesting.
>
> I think there is still lots of room for smaller RTOS in the long run,
> but it's likely that the 'MPU + external DRAM' design point will
> shift further to Linux, as there isn't really a benefit in squeezing
> in anything smaller when the minimum is 32MB or 128MB of
> RAM, depending on the interface.
>
> For on-chip eDRAM or SRAM based MPUs, that doesn't hold
> true, the memory size is what drives the cost here.
>
>          Arnd