linux-kernel - Re: [PATCH v4 00/16] Basic StarFive JH7100 RISC-V SoC support

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Date:   Tue, 16 Nov 2021 18:28:41 +0100
From:   Emil Renner Berthing <kernel@...il.dk>
To:     Arnd Bergmann <arnd@...db.de>, Palmer Dabbelt <palmer@...belt.com>
Cc:     linux-riscv <linux-riscv@...ts.infradead.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Linus Walleij <linus.walleij@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Maximilian Luz <luzmaximilian@...il.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Drew Fustini <drew@...gleboard.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michael Zhu <michael.zhu@...rfivetech.com>,
        Fu Wei <tekkamanninja@...il.com>,
        Anup Patel <anup.patel@....com>,
        Matteo Croce <mcroce@...rosoft.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 00/16] Basic StarFive JH7100 RISC-V SoC support

On Tue, 16 Nov 2021 at 17:08, Arnd Bergmann <arnd@...db.de> wrote:
> On Tue, Nov 16, 2021 at 4:01 PM Emil Renner Berthing <kernel@...il.dk> wrote:
> >
> > This series adds support for the StarFive JH7100 RISC-V SoC. The SoC has
> > many devices that need non-coherent dma operations to work which isn't
> > upstream yet[1], so this just adds basic support to boot up, get a
> > serial console, blink an LED and reboot itself. Unlike the Allwinner D1
> > this chip doesn't use any extra pagetable bits, but instead the DDR RAM
> > appears twice in the memory map, with and without the cache.
> >
> > The JH7100 is a test chip for the upcoming JH7110 and about 300 BeagleV
> > Starlight Beta boards were sent out with them as part of a now cancelled
> > BeagleBoard.org project. However StarFive has produced more of the
> > JH7100s and more boards will be available[2] to buy. I've seen pictures
> > of the new boards now, so hopefully before the end of the year.
> >
> > This series is also available at
> > https://github.com/esmil/linux/commits/starlight-minimal
> > ..but a more complete kernel including drivers for non-coherent
> > peripherals based on this series can be found at
> > https://github.com/starfive-tech/linux/tree/visionfive
> >
> > [1]: https://lore.kernel.org/linux-riscv/20210723214031.3251801-2-atish.patra@wdc.com/
> > [2]: https://www.linkedin.com/pulse/starfive-release-open-source-single-board-platform-q3-2021-starfive/
>
> Thanks for adding me to Cc, I've had a look at the series and didn't
> see anything
> wrong with it, and I'm happy to merge it through the SoC tree for the
> initial support
> in 5.17, provided you get an Ack from the arch/riscv maintainers for it.

Cool!

@Palmer, do you mind looking through this? Probably patch 1, 15 and 16
are the most relevant to you.

> Regarding the coherency issue, it's a bit sad to see yet another hacky
> workaround
> in the hardware, but as you say this is unrelated to the driver
> series. I'd actually
> argue that this one isn't that different from the other hack you
> describe, except
> this steals the pagetable bits from the address instead of the reserved flags...

Yeah, it's definitely a hack, but at least it's not using bits the
spec said was reserved. Hopefully the JH7110 will be fully coherent or
maybe implement the new Svpbmt extension.

/Emil


/Emil