Re: [PATCH v2 2/2] arm64: dts: Add Mediatek X20 Development Board support

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

Hi Matthias,

On Mon, Jul 16, 2018 at 03:24:44PM +0200, Matthias Brugger wrote:
> Hi Manivanna,
> 
> On 05/06/18 18:34, Manivannan Sadhasivam wrote:
> > Add initial device tree support for Mediatek X20 Development Board
> > based on MT6797 Deca core SoC. This board is one of the 96Boards
> > Consumer Edition platform.
> > 
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > ---
> >  arch/arm64/boot/dts/mediatek/Makefile         |  1 +
> >  .../boot/dts/mediatek/mt6797-x20-dev.dts      | 33 +++++++++++++++++++
> >  2 files changed, 34 insertions(+)
> >  create mode 100644 arch/arm64/boot/dts/mediatek/mt6797-x20-dev.dts
> > 
> > diff --git a/arch/arm64/boot/dts/mediatek/Makefile b/arch/arm64/boot/dts/mediatek/Makefile
> > index ac17f60f998c..5b7fd6ad96e4 100644
> > --- a/arch/arm64/boot/dts/mediatek/Makefile
> > +++ b/arch/arm64/boot/dts/mediatek/Makefile
> > @@ -3,5 +3,6 @@ dtb-$(CONFIG_ARCH_MEDIATEK) += mt2712-evb.dtb
> >  dtb-$(CONFIG_ARCH_MEDIATEK) += mt6755-evb.dtb
> >  dtb-$(CONFIG_ARCH_MEDIATEK) += mt6795-evb.dtb
> >  dtb-$(CONFIG_ARCH_MEDIATEK) += mt6797-evb.dtb
> > +dtb-$(CONFIG_ARCH_MEDIATEK) += mt6797-x20-dev.dtb
> >  dtb-$(CONFIG_ARCH_MEDIATEK) += mt7622-rfb1.dtb
> >  dtb-$(CONFIG_ARCH_MEDIATEK) += mt8173-evb.dtb
> > diff --git a/arch/arm64/boot/dts/mediatek/mt6797-x20-dev.dts b/arch/arm64/boot/dts/mediatek/mt6797-x20-dev.dts
> > new file mode 100644
> > index 000000000000..2c09ca95d9e2
> > --- /dev/null
> > +++ b/arch/arm64/boot/dts/mediatek/mt6797-x20-dev.dts
> > @@ -0,0 +1,33 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Device Tree Source for MediaTek X20 Development Board
> > + *
> > + * Copyright (C) 2018, Linaro Ltd.
> > + *
> > + */
> > +
> > +/dts-v1/;
> > +
> > +#include "mt6797.dtsi"
> > +
> > +/ {
> > +	model = "Mediatek X20 Development Board";
> > +	compatible = "archermind,mt6797-x20-dev", "mediatek,mt6797";
> > +
> > +	aliases {
> > +		serial0 = &uart1;
> > +	};
> 
> Sorry for the late answer.
> Why did you use uart1 instead of uart0?
> I know that uart0 is used by the bootloader, but because of their exotic flash
> procedure I find it quite useful to see this messages in my serial connection.
> Of course you can only use 921600 baudrate then.
> 

The reason is, most of the Mezzanine boards use USB to UART bridge on the
UART1 port available on the Low Speed Expansion header. Additionally, the
convention followed by most of the Consumer Edition 96Boards is to use UART1
as the debug serial port. That's why eventhough the bootloader is using UART0,
I forced the kernel to use UART1.

> > +
> > +	memory@40000000 {
> > +		device_type = "memory";
> > +		reg = <0 0x40000000 0 0x1e605000>;
> 
> How comes this strange number for the memory size?
> 

Actually, the memory size is extracted from the downstream kernel [1].

> BTW do you know the differences between the EVB board and the x20 one?
> I used the evb dts for booting up to now.
> 

Sorry, I don't know the difference between both boards!

Thanks,
Mani

[1] https://github.com/helio-x20/linux/blob/helio-x20/arch/arm64/boot/dts/amt6797_64_open.dts#L8

> Best regards,
> Matthias
> 
> > +	};
> > +
> > +	chosen {
> > +		stdout-path = "serial0:115200n8";
> > +	};
> > +};
> > +
> > +&uart1 {
> > +	status = "okay";
> > +};
> >