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

[Alexey Brodkin]

Hi Alexander, Tom,

> -----Original Message-----
> From: Alexander Graf [mailto:agraf at suse.de]
> Sent: Tuesday, July 17, 2018 4:33 PM
> To: Tom Rini <trini at konsulko.com>
> Cc: Wolfgang Denk <wd at denx.de>; Felix Brack <fb at ltec.ch>; u-boot at lists.denx.de; Stefan Roese <sr at denx.de>; Alexey Brodkin
> <Alexey.Brodkin at synopsys.com>; Michal Simek <michal.simek at xilinx.com>
> Subject: Re: [U-Boot] [PATCH] serial: ns16550: Add register shift variable
> 
> 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.

Here's the driver:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tty/serial/omap-serial.c

-Alexey