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

[Alexey Brodkin <Alexey.Brodkin@synopsys.com>]

Hi Felix,

> -----Original Message-----
> From: Felix Brack [mailto:fb at ltec.ch]
> Sent: Sunday, July 15, 2018 5:02 PM
> To: Alexey Brodkin <Alexey.Brodkin@synopsys.com>; Tom Rini <trini@konsulko.com>
> Cc: u-boot at lists.denx.de; Stefan Roese <sr@denx.de>; Alexander Graf <agraf@suse.de>; Michal Simek <michal.simek@xilinx.com>;
> Wolfgang Denk <wd@denx.de>
> Subject: Re: [U-Boot] [PATCH] serial: ns16550: Add register shift variable
> 
> Hi Alexey,
> 
> On 15.07.2018 10:43, Alexey Brodkin wrote:
> > Hi Tom, Felix, all
> >
> >> -----Original Message-----
> >> From: Tom Rini [mailto:trini at konsulko.com]
> >> Sent: Saturday, July 14, 2018 6:50 PM
> >> To: Wolfgang Denk <wd@denx.de>
> >> Cc: Felix Brack <fb@ltec.ch>; u-boot at lists.denx.de; Stefan Roese <sr@denx.de>; Alexey Brodkin <Alexey.Brodkin@synopsys.com>;
> >> Alexander Graf <agraf@suse.de>; Michal Simek <michal.simek@xilinx.com>
> >> Subject: Re: [U-Boot] [PATCH] serial: ns16550: Add register shift variable
> >>
> >> On Sat, Jul 14, 2018 at 12:47:21PM +0200, Wolfgang Denk wrote:
> >>> Dear Felix,
> >>>
> >>> In message <1531492980-16543-1-git-send-email-fb@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.
> >
> > Any chance to get a reference to the commit in Linux kernel that introduces that change?
> >
> In fact I believe that the <reg-shift> property never existed in the
> am33xx.dtsi file from Linux. U-Boot commit 85cf0e6299 shows that the
> property has been added to U-Boot's am33xx.dtsi file. The commit log
> clearly states why this happened:
> 
> "With the commit 'c7b9686d5d48 ("ns16550: unify serial_omap")' all
> TI platforms are broken with DM/DT boot as ns16550 driver expects
> reg-shift from DT which is not populated for TI platforms.
> Earlier it worked as it was hard coded to 2 in serial-omap
> driver. So adding the reg-shift to serial nodes for dra7, am4372
> and am33xx dtsi files. Tested this patch on am437x-sk-evm,
> am437x-gp-evm, am335x-boneblack, dra74x-evm and dra72x-evm."

Ok so this has nothing to do with changes in Linux kernel I guess.
Why don't we go the other way around and not just submit
a change to .dts files in Linux kernel that are missing required properties?

-Alexey