linux-kernel - Re: [PATCH 23/31] nds32: Device tree support

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Message-ID: <CAK8P3a1C-FUkJePjueRF1hFDRLr8OQ3KL89K_kvmBdbrjhvvVQ@mail.gmail.com>
Date:   Wed, 8 Nov 2017 10:53:28 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Greentime Hu <green.hu@...il.com>
Cc:     greentime@...estech.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Marc Zyngier <marc.zyngier@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Networking <netdev@...r.kernel.org>,
        Vincent Chen <vincentc@...estech.com>
Subject: Re: [PATCH 23/31] nds32: Device tree support

On Wed, Nov 8, 2017 at 6:55 AM, Greentime Hu <green.hu@...il.com> wrote:
> From: Greentime Hu <greentime@...estech.com>
>
> Signed-off-by: Vincent Chen <vincentc@...estech.com>
> Signed-off-by: Greentime Hu <greentime@...estech.com>
> ---
>  arch/nds32/boot/dts/Makefile   |    8 ++++++
>  arch/nds32/boot/dts/ae3xx.dts  |   55 ++++++++++++++++++++++++++++++++++++
>  arch/nds32/boot/dts/ag101p.dts |   60 ++++++++++++++++++++++++++++++++++++++++
>  arch/nds32/kernel/devtree.c    |   45 ++++++++++++++++++++++++++++++
>  4 files changed, 168 insertions(+)
>  create mode 100644 arch/nds32/boot/dts/Makefile
>  create mode 100644 arch/nds32/boot/dts/ae3xx.dts
>  create mode 100644 arch/nds32/boot/dts/ag101p.dts
>  create mode 100644 arch/nds32/kernel/devtree.c
>
> diff --git a/arch/nds32/boot/dts/Makefile b/arch/nds32/boot/dts/Makefile
> new file mode 100644
> index 0000000..d31faa8
> --- /dev/null
> +++ b/arch/nds32/boot/dts/Makefile
> @@ -0,0 +1,8 @@
> +ifneq '$(CONFIG_NDS32_BUILTIN_DTB)' '""'
> +BUILTIN_DTB := $(patsubst "%",%,$(CONFIG_NDS32_BUILTIN_DTB)).dtb.o
> +else
> +BUILTIN_DTB :=
> +endif
> +obj-$(CONFIG_OF) += $(BUILTIN_DTB)

For new architectures, I think it's better to not support built-in dtb
but instead require the
boot loader to be aware of device trees.

> +clean-files := *.dtb *.dtb.S
> diff --git a/arch/nds32/boot/dts/ae3xx.dts b/arch/nds32/boot/dts/ae3xx.dts
> new file mode 100644
> index 0000000..b6c85dc
> --- /dev/null
> +++ b/arch/nds32/boot/dts/ae3xx.dts
> @@ -0,0 +1,55 @@
> +/dts-v1/;
> +/ {
> +       compatible = "nds32 ae3xx";

ae3xx looks like a wildcard name for multiple boards. Please always
have compatible
names without wildcards. You usually also want to list both the SoC
and the board
here.

> +       #address-cells = <1>;
> +       #size-cells = <1>;
> +       interrupt-parent = <&intc>;
> +
> +       chosen {
> +               bootargs = "console=ttyS0,38400n8 earlyprintk=uart8250-32bit,0xf0300000 debug loglevel=7";
> +       };

Remove the earlyprintk option from the bootargs here, regular boards
should never rely
on earlyprintk. The "earlycon" support in the uart drivers works
almost as well (it starts
slightly later in the boot process), and it will pick up the uart from
the chosen/stdout-path
property.

> +       if (!params || !early_init_dt_scan(params)) {
> +               pr_crit("\n"
> +                       "Error: invalid device tree blob at (virtual address 0x%p)\n"
> +                       "The dtb must be 8-byte aligned and must not exceed 8 KB in size\n"
> +                       "\nPlease check your bootloader.", params);

What is the 8KB limit for the dtb for? This sounds really limiting
once you get to
more complex SoCs.

       Arnd