Re: [RFC PATCH V4 6/6] riscv: soc: Add Allwinner SoC kconfig option

[Arnd Bergmann <arnd@arndb.de>]

On Tue, Sep 14, 2021 at 4:36 AM Guo Ren <guoren@kernel.org> wrote:
> On Tue, Sep 14, 2021 at 2:49 AM Randy Dunlap <rdunlap@infradead.org> wrote:
> > On 9/13/21 2:20 AM, Guo Ren wrote:
> > > On Mon, Sep 13, 2021 at 4:45 PM Maxime Ripard <maxime@cerno.tech> wrote:
> > >> On Sat, Sep 11, 2021 at 05:21:39PM +0800, guoren@kernel.org wrote:
> > >>> From: Liu Shaohua <liush@allwinnertech.com>
> > >>>
> > >>> Add Allwinner kconfig option which selects SoC specific and common
> > >>> drivers that is required for this SoC.
> > >>>
> > >>> Allwinner D1 uses custom PTE attributes to solve non-coherency SOC
> > >>> interconnect issues for dma synchronization, so we set the default
> > >>> value when SOC_SUNXI selected.
> > >>>
> > >>>
> > >>> +config SOC_SUNXI
> > >>> +     bool "Allwinner SoCs"
> > >>> +     depends on MMU
> > >>> +     select DWMAC_GENERIC
> > >>> +     select ERRATA_THEAD
> > >>> +     select RISCV_DMA_NONCOHERENT
> > >>> +     select RISCV_ERRATA_ALTERNATIVE
> > >>> +     select SERIAL_8250
> > >>> +     select SERIAL_8250_CONSOLE
> > >>> +     select SERIAL_8250_DW
> > >>> +     select SIFIVE_PLIC
> > >>> +     select STMMAC_ETH
> > >>> +     help
> > >>> +       This enables support for Allwinner SoC platforms like the D1.
> > >>> +
> > >>
> > >> I'm not sure we should select the drivers there. We could very well
> > >> imagine a board without UART, or even more so without ethernet.
> > > We just want people could bring D1 up easier, 8250 is the basic component.
> > >
> > >
> > >>
> > >> These options should be in the defconfig.
> >
> > Agreed, using a defconfig is the right way to do this.
> Put 8250 related configs into arch/riscv/configs/defconfig?

I think that would be best, as well as the STMMAC_ETH and
DWMAC_GENERIC options.

If all RISC-V chips are required to have a 8250 compatible uart,
selecting it from CONFIG_RISCV would work as well, but for
consistency I'd give users the option to leave it out, just like
any other driver that is not required to have a useful system.

>  @Palmer Dabbelt @Arnd Bergmann, How do you think about that?
> (defconfig or Kconfig.soc)
> My purpose is when people make the Image from riscv/defconfig, then
> the Image could run on all platforms include D1.

I would try to keep the Kconfig.soc as short as possible. As a general
rule, only use 'select' to enable symbols that are otherwise not user
visible, such as the specific errata if you want to hide them. For individual
SoCs, I prefer not having separate Kconfig options, but instead have
those per driver. We have some SoC families that have part specific
options elsewhere, e.g. drivers/soc/renesas/Kconfig, but I'd only add
those if you can't avoid it. Having it in drivers/soc/ may be better for
sunxi than spreading them over arch/{arm,arm64,riscv}.

Some subsystem maintainers want drivers to be selected by the SoC
option, this is why you need the 'select SIFIVE_PLIC', but usually
the drivers are selectable with a 'depends on ARCH_SUNXI ||
COMPILE_TEST' and enabled in the defconfig.

If you want to get fancy, you can use something like:

config RESET_SUNXI
        bool "Allwinner SoCs Reset Driver" if COMPILE_TEST && !ARCH_SUNXI
        default ARCH_SUNXI

This will make an option that
 - always enabled when the platform is built-in
 - user selectable when compile-testing for any other platform
 - always disabled otherwise

       Arnd