[U-Boot] [linux-sunxi] [PATCH v4 00/26] sunxi: Allwinner A64: SPL support

[Jagan Teki]

On Tue, Jan 3, 2017 at 2:52 PM, jonsmirl at gmail.com <jonsmirl at gmail.com> wrote:
> On Tue, Jan 3, 2017 at 5:41 AM, Jagan Teki <jagannadh.teki at gmail.com> wrote:
>> On Tue, Jan 3, 2017 at 3:38 AM, jonsmirl at gmail.com <jonsmirl at gmail.com> wrote:
>>> I recently ran into a probably with the UARTs on the A64. Many
>>> Bluetooth modules (like Ampak) use the UART. The data rate of EDR BT
>>> is 3Mb/s with about 2.1Mb/s though put. To handle this most systems
>>> set the speed of the BT UART to 3Mb/s.
>>>
>>> By default the Allwinner UART clock input is OSC24. When using OSC24
>>> the maximum speed the UART can be set to is 1.5Mb/s. The clock input
>>> (apb2) can be changed over to PERIPH0x2 (1.2ghz) via the device tree
>>> and 3Mb/s is then supported.
>>>
>>> But... there's a problem, UART0 (the console) is using the same master
>>> clock source. So when you change the clock input over to PERIPH0x2 the
>>> console stops working. There is no mechanism in Linux to handle this
>>> clock source change and adjust the dividers on active uarts. So it
>>> would be best if this master clock was set very early in u-boot and
>>> then the console is adjusted to use it.
>>>
>>> Are there any downsides to making this change in u-boot?
>>
>> I don't understand, did you find this behaviour with these SPL changes
>> or general sunxi u-boot?

I think, this issue need to resolve, Andre any comments?

>
> Previously the boot console uart0 was getting setup in the SPL code. I
> have not been closely following these changes, is that still true?
>
> Changing the clock parent needs to be done before uart0 is
> initialized. Changing this parent should have no other impact on
> u-boot other than changing the clock divisor uart0 is using.
>
> Once Linux is up, the Linux uart code will see the changed clock
> parent and allow higher baud rates to be set.
>
> This clock parent also impacts the I2C clocks, but I don't believe I2C
> is enabled in A64 uboot.

Jagan.