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

From: Emil Renner Berthing
Date: Tue Nov 16 2021 - 12:29:04 EST

On Tue, 16 Nov 2021 at 17:08, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Tue, Nov 16, 2021 at 4:01 PM Emil Renner Berthing <kernel@xxxxxxxx> 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
> > 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
> >
> > ..but a more complete kernel including drivers for non-coherent
> > peripherals based on this series can be found at
> >
> >
> > [1]:
> > [2]:
> 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.


@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.