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

[Tom Rini]

On Tue, Jul 17, 2018 at 03:33:15PM +0200, Alexander Graf wrote:
> 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.

Yes and no.  For a number of years now the omap-only (ttyOx) driver has
been deprecated and the generic ns1665x driver is valid.  What does the
ns1655x driver do here?

-- 
Tom
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