Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752437AbdLKOWp (ORCPT ); Mon, 11 Dec 2017 09:22:45 -0500 Received: from mx08-00178001.pphosted.com ([91.207.212.93]:33104 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751512AbdLKOWk (ORCPT ); Mon, 11 Dec 2017 09:22:40 -0500 Subject: Re: [PATCH 1/6] ARM: stm32: prepare stm32 family to welcome armv7 architecture To: Arnd Bergmann , Linus Walleij CC: Russell King , Rob Herring , Maxime Coquelin , Alexandre Torgue , Linux ARM , "linux-kernel@vger.kernel.org" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" References: <1512742277-28205-1-git-send-email-ludovic.Barre@st.com> <1512742277-28205-2-git-send-email-ludovic.Barre@st.com> From: Ludovic BARRE Message-ID: <9ef92e81-fdd2-fa71-1e87-f797a191d215@st.com> Date: Mon, 11 Dec 2017 15:22:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.75.127.49] X-ClientProxiedBy: SFHDAG2NODE3.st.com (10.75.127.6) To GPXDAG6NODE4.st.com (10.75.127.80) X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-12-11_06:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2148 Lines: 52 On 12/11/2017 02:40 PM, Arnd Bergmann wrote: > On Mon, Dec 11, 2017 at 11:25 AM, Linus Walleij > wrote: >> On Fri, Dec 8, 2017 at 3:11 PM, Ludovic Barre wrote: >> >>> From: Ludovic Barre >>> >>> 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 > > 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 >