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

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Date:   Mon, 11 Dec 2017 15:22:00 +0100
From:   Ludovic BARRE <ludovic.barre@...com>
To:     Arnd Bergmann <arnd@...db.de>,
        Linus Walleij <linus.walleij@...aro.org>
CC:     Russell King <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: 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
> <linus.walleij@...aro.org> wrote:
>> On Fri, Dec 8, 2017 at 3:11 PM, Ludovic Barre <ludovic.Barre@...com> wrote:
>>
>>> From: Ludovic Barre <ludovic.barre@...com>
>>>
>>> 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@...com>
> 
> 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
>