linux-kernel - Re: [PATCH 2/2] ARM: dts: sun8i: enable UART1 for iNet D978 Rev2 board

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Date:   Thu, 25 Aug 2016 16:17:50 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Icenowy Zheng <icenowy@...c.xyz>,
        Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Russell King <linux@...linux.org.uk>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ARM: dts: sun8i: enable UART1 for iNet D978 Rev2
 board

Hi,

On 25-08-16 16:12, Icenowy Zheng wrote:
>
>
> 25.08.2016, 16:03, "Maxime Ripard" <maxime.ripard@...e-electrons.com>:
>> Hi,
>>
>> On Thu, Aug 25, 2016 at 02:57:24PM +0800, Icenowy Zheng wrote:
>>>  >>>>   diff --git a/arch/arm/boot/dts/sun8i-a33-inet-d978-rev2.dts b/arch/arm/boot/dts/sun8i-a33-inet-d978-rev2.dts
>>>  >>>>   index 78823d8..3ac22d4 100644
>>>  >>>>   --- a/arch/arm/boot/dts/sun8i-a33-inet-d978-rev2.dts
>>>  >>>>   +++ b/arch/arm/boot/dts/sun8i-a33-inet-d978-rev2.dts
>>>  >>>>   @@ -48,6 +48,10 @@
>>>  >>>>            model = "INet-D978 Rev 02";
>>>  >>>>            compatible = "primux,inet-d978-rev2", "allwinner,sun8i-a33";
>>>  >>>>
>>>  >>>>   + aliases {
>>>  >>>>   + serial1 = &uart1;
>>>  >>>>   + };
>>>  >>>>   +
>>>  >>>
>>>  >>>  Is there any other UART in the system?
>>>  >>
>>>  >>  serial0 is defined in sun8i-reference-design-tablet.dtsi, as r_uart.
>>>  >
>>>  > If your board does not have r_uart pads, then the right thing to do
>>>  > would be to disable it. You can then have uart1 as serial0.
>>>
>>>  I don't know it. The RX/TX is wired on PF2/PF4 on the board (UART0 muxed with
>>>  MMC)
>>
>> Then you don't support it and you need to disable it.
>>
>>>  But many codes will require a ttyS0 as console... So I think the
>>>  bluetooth should be located at ttyS1...
>>
>> Most of them would use /dev/console anyway. What do you have in mind?
>
> As a general configuration, /dev/ttyS0 will be indicated as the default console=
> value... (Otherwise more boards will fail)
>
> Or maybe we can specify uart0 as serial0, and leave it as disabled? (Thus if the
> debug port is needed, we can easily apply a overlay with &mmc0 status as disabled,
> and &uart0 status as okay)
>
> On all my A33 boards, the official boot0, u-boot all uses uart0 as debugging port.

If no uart is available (and being muxed with the mmc counts as not being available)
then you should not have any serial alias in the dts.

In u-boot you need to use:

# CONFIG_REQUIRE_SERIAL_CONSOLE is not set

In the defconfig in this case, otherwise u-boot is going to be unhappy about
not having a serial console.

Regards,

Hans