[U-Boot] [RFC] Merge all ns16550 dm serial drivers into one

[Bin Meng]

On Sat, Aug 15, 2015 at 12:59 AM, Simon Glass <sjg at chromium.org> wrote:
> Hi Stephen,
>
> On 14 August 2015 at 10:58, Stephen Warren <swarren at wwwdotorg.org> wrote:
>> On 08/14/2015 10:50 AM, Simon Glass wrote:
>>>
>>> Hi Bin,
>>>
>>> On 14 August 2015 at 03:18, Bin Meng <bmeng.cn at gmail.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> Currently there are 5 dm serial drivers, all of which are ns16550
>>>> compatible drivers. They are:
>>>>
>>>>    serial_omap.c
>>>>    serial_dw.c
>>>>    serial_tegra.c
>>>>    serial_x86.c
>>>>    serial_ppc.c
>>>>
>>>> All these drivers are pretty much similar. I think we can justmerge
>>>> these into one ns16550 driver.
>>>>
>>>> If you think this is necessary, I will send a patch series to do this.
>>>
>>>
>>> The tegra one is there because it needs an input clock and Stephen
>>> didn't want to add this to the device tree binding (the kernel has a
>>> clock framework which gets around this problem).
>>>
>>> After that I followed the same pattern. I would support updating the
>>> binding to support an input clock. Even with the new clock framework
>>> in U-Boot it might be painful to fit it into SPL in some cases.
>>
>>
>> The clock is already in the DT, in both Linux and U-Boot's copy, at least
>> for Tegra DTs:
>>
>>         uarta: serial at 0,70006000 {
>>                 compatible = "nvidia,tegra124-uart", ...
>> ...
>>                 clocks = <&tegra_car TEGRA124_CLK_UARTA>;
>>
>
> I mean the clock-frequency property. However if there is a plan to
> implement the clock framework in U-Boot that would be good too.
>

The clock-frequency is a fixed value on x86 super i/o chipset, and
fixed on the PCI bus too. But for ARM and PPC, it might get
dynamically calculated due to different PLL settings. We can implement
a _weak function like the one in serial_ppc.c get_serial_clock() to
initialize plat->clock with its return value. The _weak function gets
clock-frequency from device tree. If there is not, platform codes
which uses the ns16550 driver should provide the implementation of
get_serial_clock(). Thoughts?

Regards,
Bin