[U-Boot] [PATCH] serial: ns16550: Add register shift variable

[Alexander Graf]

On 07/17/2018 03:25 PM, Tom Rini wrote:
> On Mon, Jul 16, 2018 at 02:53:26PM +0200, Alexander Graf wrote:
>> On 07/14/2018 05:49 PM, Tom Rini wrote:
>>> On Sat, Jul 14, 2018 at 12:47:21PM +0200, Wolfgang Denk wrote:
>>>> Dear Felix,
>>>>
>>>> In message <1531492980-16543-1-git-send-email-fb at ltec.ch> you wrote:
>>>>> The motivation for writing this patch originates in the
>>>>> effort of synchronizing U-Boot DT to Linux DT for am33xx SOCs.
>>>>> The current am33xx.dtsi file from U-Boot defines the <reg-shift>
>>>>> property for all UART nodes. The actual (4.18+) am33xx.dtsi
>>>>> file from Linux does not define <reg-shift> anymore. To prevent
>>>>> (probably difficult) changes in many .dts and .dtsi files once
>>>>> the synchronization is done, one can use this new variable. For
>>>>> the pdu001 board, for example, SYS_NS16550_REG_SHIFT is set
>>>>> to 2; no need to clutter U-Boot and board specific dts files
>>>>> with <reg-shift> properties.
>>>> Does this mean that U-Boot will not be able to use the same DTB as
>>>> Linux?
>>> To be clear, it's the other way around.  We can't use the Linux dtb/dts
>>> files as they've dropped (and in other cases, aren't adding) these
>>> properties as it's handled differently.
>> What does "differently" mean? Linux tries quite hard to be platform
>> agnostic, so a per-build-target #define surely isn't what they're doing.
> Yes, what exactly is the Linux kernel doing here?


Linux has a completely separate driver for omap3 (which is wrong too). 
But in a nutshell, it basically determines the shift value by the 
"compatible" string, so we should too.


Alex