[coreboot] [PATCH 2/4] Enable TSC calibration with timer2 by default.

Kevin O'Connor kevin at koconnor.net
Wed Sep 8 02:23:30 CEST 2010

On Tue, Sep 07, 2010 at 09:07:36AM +0200, Patrick Georgi wrote:
> Am 07.09.2010 01:23, schrieb Kevin O'Connor:
> > Enable TSC_X86RDTSC_CALIBRATE_WITH_TIMER2 by default.  Without this
> > set, almost all boards use the inb(0x80) method.  Unfortunately, that
> > method takes over a second to calibrate, and it's results are not as
> > reliable.
> > 
> > There is a chance that some boards may not work well with the timer2
> > method.  This is likely rare, because both libpayload and seabios use
> > the timer2 method unconditionally and there has not been reports of an
> > issue.  Should a board not support the more accurate timer2 mechanism,
> > it will need to be updated to actively disable it.
> How about this instead? It allows boards that require the workaround to
> simply "select" it.
> Signed-off-by: Patrick Georgi <patrick.georgi at coresystems.de>

That looks like a better approach.

Acked-by: Kevin O'Connor <kevin at koconnor.net>

As an aside, I'm not sure of the value of TSC based delays if
inb(0x80) is used to time it.  If the code assumes inb(0x80) is 1
usecond, I'd think it could as easily use UDELAY_IO instead.  I guess
we'll need to see if any boards need the new TSC_CALIBRATE_WITH_IO


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