linux-kernel - Re: [PATCH v5 0/9] Add initial support for the i.MXRTxxxx SoC family starting from i.IMXRT1050 SoC.

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Message-ID: <CAK8P3a29tzgd_4WncippZBEJra9n0bQTysBkPBp_WA0sb28gTg@mail.gmail.com>
Date:   Thu, 16 Dec 2021 09:26:20 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Jesse Taube <mr.bossman075@...il.com>
Cc:     NXP Linux Team <linux-imx@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Sascha Hauer <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Dong Aisheng <aisheng.dong@....com>,
        Stefan Agner <stefan@...er.ch>,
        Linus Walleij <linus.walleij@...aro.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
        SoC Team <soc@...nel.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Abel Vesa <abel.vesa@....com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        giulio.benetti@...ettiengineering.com,
        Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@...hiba.co.jp>,
        linux-clk <linux-clk@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v5 0/9] Add initial support for the i.MXRTxxxx SoC family
 starting from i.IMXRT1050 SoC.

On Wed, Dec 15, 2021 at 11:05 PM Jesse Taube <mr.bossman075@...il.com> wrote:
>
> This patchset contains:
> - i.MXRT10xx family infrastructure
> - i.MXRT1050 pinctrl driver adaption
> - i.MXRT1050 clock driver adaption
> - i.MXRT1050 sd-card driver adaption
> - i.MXRT1050 uart driver adaption
> - i.MXRT1050-evk basic support
>
> The i.MXRTxxxx family that could have support by Linux actually spreads
> from i.MXRT1020 to i.MXRT1170 with the first one supporting 1 USB OTG &
> 100M ethernet with a cortex-M7@...Mhz up to the latter with i.MXRT1170
> with cortex-M7@...z and cortex-M4@...Mhz, 2MB of internal SRAM, 2D GPU,
> 2x 1Gb and 1x 100Mb ENET. The i.MXRT family is NXP's answer to
> STM32F7XX, as it uses only simple SDRAM, it gives the chance of a 4 or
> less layer PCBs. Seeing that these chips are comparable to the
> STM32F7XXs which have linux ported to them it seems reasonable to add
> support for them.
>
> Giving Linux support to this family should ease the development process,
> instead of using a RTOS they could use Embedded Linux allowing for more
> portability, ease of design and will broaden the scope of people using
> embedded linux.
>
> The EVK has very little SDRAM, generally 32MB starting from
> i.MXRT1020(the lowest P/N), although the i.MXRT1160/70 provide instead
> 64MB of SDRAM for more functionality.
>
> At the moment we do not support XIP for either u-boot or Linux but it
> should be done in the future. XIP will also save SDRAM.
>
> Another interesting fact is the amount of internal SRAM, as the P/N
> increases the SRAM will reach up to 2MB(some could be for cache and
> some would be for video).
>
> Also, some parts have embed flash of 4MB that can be used for
> u-boot/Linux, if both correctly sized it will leave the SDRAM free.
>
> External flash can be Quad SPI and HyperFlash, so throughput would be
> decent.
>
> The i.MXRT11xx series supports MIPI interface too.
>
> The family in general provide CAN bus, audio I/O, 1 or more
> USB(otg/host), 1 or more 100Mb/1Gb ethernet, camera interface, sd-card.
>
> All this can be used for simple GUIs, web-servers, point-of-sale
> stations, etc.

This looks all good to me now, but the drivers need to be reviewed by the
respective subsystem maintainers before we can merge it into the soc
tree. As with other new SoCs, I'm happy to merge the support as a combined
pull request that includes the drivers provided that the driver subsystem
maintainers have reviewed them.

Ideally the i.MX maintainers would pick up your series into a separate
branch and send that to soc@...nel.org the same way as the other topic
branches that are usually split out between DT, drivers, soc code etc.

With the Christmas break coming up, the timing may not be sufficient
before I'm off next week, so it may end up too late for 5.17 but should
be fine for 5.18.

As a more general comment, it's always nice to see newly added SoC
platforms, especially when they are this well implemented and done
by hobbyists. However, I do think you are being overly optimistic
as to how useful this is going to be to other people: interest in NOMMU
ARM platforms has dropped a lot over the past 5 years, and as far as I
can tell, it is only being kept alive for existing stm32 customers
as the economics do not favor Linux on Cortex-M for new products
compare to Linux on Cortex-A or some RTOS on Cortex-M.

The existing users will inevitably stop updating their kernels at some
point, and then it's most likely just you and Vladimir Murzin that care.

       Arnd