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

On 12/11/2017 02:40 PM, Arnd Bergmann wrote:

On Mon, Dec 11, 2017 at 11:25 AM, Linus Walleij
[off-list ref] wrote:

quoted

On Fri, Dec 8, 2017 at 3:11 PM, Ludovic Barre [off-list ref] wrote:

quoted

From: Ludovic Barre <redacted>

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 <redacted>

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

quoted

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