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

[Heinrich Schuchardt]

On 9/13/21 10:45 AM, Maxime Ripard wrote:
> Hi,
>
> On Sat, Sep 11, 2021 at 05:21:39PM +0800, guoren@xxxxxxxxxx wrote:
> > From: Liu Shaohua <liush@xxxxxxxxxxxxxxxxx>
> >
> > 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.
> >
> > Signed-off-by: Liu Shaohua <liush@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > Signed-off-by: Wei Fu <wefu@xxxxxxxxxx>
> > Cc: Anup Patel <anup.patel@xxxxxxx>
> > Cc: Atish Patra <atish.patra@xxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Chen-Yu Tsai <wens@xxxxxxxx>
> > Cc: Drew Fustini <drew@xxxxxxxxxxxxxxx>
> > Cc: Maxime Ripard <maxime@xxxxxxxxxx>
> > Cc: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>
> > Cc: Wei Wu <lazyparser@xxxxxxxxx>
> > ---
> >   arch/riscv/Kconfig.socs      | 15 +++++++++++++++
> >   arch/riscv/configs/defconfig |  1 +
> >   2 files changed, 16 insertions(+)
> >
> > diff --git a/arch/riscv/Kconfig.socs b/arch/riscv/Kconfig.socs
> > index 30676ebb16eb..8721c000ef23 100644
> > --- a/arch/riscv/Kconfig.socs
> > +++ b/arch/riscv/Kconfig.socs
> > @@ -70,4 +70,19 @@ config SOC_CANAAN_K210_DTB_SOURCE
> >   
> >   endif
> >   
> > +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.

The draft of the RISC-V platform specification is available here:
https://github.com/riscv/riscv-platform-specs/blob/main/riscv-platform-spec.adoc#uartserial-console

The specification requires in section "2.1.5.1. UART/Serial Console" 
that on platforms with a rich operating system (e.g. Linux) you have a 
serial console. Hence requiring 8250 support for the D1 CPU is justified.

In the riscv defconfig as of v5.14 we have:

CONFIG_SERIAL_8250=y
CONFIG_SERIAL_8250_CONSOLE=y
# CONFIG_SERIAL_8250_DW is not set
(Support for Synopsys DesignWare 8250 quirks)

CONFIG_SERIAL_8250_DW should be enabled (=y) in the defconfig.

As the specification requires a 16550 UART and marks 8250 as deprecated 
I expect that future Allwinner SoCs will move to 16550. Calling a 
Kconfig menu item "Allwinner SoCs" which includes all future Allwinner 
SoCs irritates me. How about CONFIG_SOC_SUNXI_D1 instead?

Why does the patch use 'depends on MMU' and does not 'select MMU'?

Best regards

Heinrich

> These options should be in the defconfig.
>
> Maxime