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SubjectRe: [PATCH v1 4/6] x86/boot: Assume MMIO if serial base address supplied via earlyprintk
On Tue, 2018-01-16 at 04:13 +0100, Ingo Molnar wrote:
> * Andy Shevchenko <> wrote:
> > If user supplied serial base address via kernel command line and
> > value
> > is higher than IO space limit (64k boundary), assume for now that
> > MMIO
> > byte access is required.
> >
> > Later we might expand or modify this if needed.
> Is this a standard pattern for serial code configuration values?

I didn't get what you meant under "standard" here.

IO space limit comes from generic io.h header and AFAIU is a hardware
limitation (outN (%dx), ...; inX (%dx); dx is 16 bit register).

Using mmio8 out of the IO space is dictated by the (modern) x86
platforms with non-standard (okay, high speed) UART location in address

Andy Shevchenko <>
Intel Finland Oy

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