[PATCH v4 5/5] arm64: dts: Add dts files for Hisilicon Hi6220 SoC

[Haojian Zhuang]

On 6 May 2015 at 17:30, Mark Rutland <mark.rutland at arm.com> wrote:
> On Wed, May 06, 2015 at 07:50:52AM +0100, Bintian wrote:
>> Hello Mark,
>>
>> On 2015/5/6 11:16, Bintian wrote:
>> > Hello Mark,
>> >
>> > On 2015/5/6 1:13, Mark Rutland wrote:
>> [...]
>> >>> +        uart0: uart at f8015000 {    /* console */
>> >>> +            compatible = "arm,pl011", "arm,primecell";
>> >>> +            reg = <0x0 0xf8015000 0x0 0x1000>;
>> >>> +            interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
>> >>> +            clocks = <&ao_ctrl HI6220_UART0_PCLK>, <&ao_ctrl
>> >>> HI6220_UART0_PCLK>;
>> >>> +            clock-names = "uartclk", "apb_pclk";
>> >>> +        };
>> >>
>> >> In a previous discussion [1] the UART on HI6220 was described as not
>> >> fully PL011 compliant, with a number of differences (e.g. the FIFO
>> >> length).
>> >>
>> >> Given that, I feel somewhat uncomfortable with the current compatible
>> >> string list. What exactly are those differences? We may need a more
>> >> specific compatible string (even if in addition to those existing ones),
>> >> or perhaps other properties.
>> > The small system can be booted and the console also works well without
>> > changing any code of driver amba-pl011.c, so I think the compatible
>> > string is OK for this patch set.
>> >
>> > Hisilicon do some performance enhancements based on PL011, but the
>> > current driver "amba-pl011.c" also works on hi6220 without those
>> > enhancements driver code.
>> Checked with Hisilicon chip designer, the UART0 is used for DEBUG
>> console and compliant with PL011 fully.
>
> I think that given that we know the UART is not quite a PL011 we should
> add an additional compatible string just in case some difference crops
> up later that is problematic.
>
> So we'd have something like:
>
>         compatible = "hisilicon,hi6220-uart", "arm,pl011", "arm,primecell";
>
> That way we can add any optimisations or workarounds later as required.
>

There's no code to handle the feature of hi6220 uart in mainline. It's
meaningless to append "hisilicon,hi6220-uart" at here. I think it's
only required
when those uart code are merged into mainline.

Regards
Haojian