linux-kernel - RE: [PATCH] firmware: export x86_64 platform flash bios region via sysfs

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Date:   Wed, 23 Jun 2021 13:22:51 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Hans-Gert Dahmen' <hans-gert.dahmen@...u.ne>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "philipp.deppenwiese@...u.ne" <philipp.deppenwiese@...u.ne>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: RE: [PATCH] firmware: export x86_64 platform flash bios region via
 sysfs

From: Hans-Gert Dahmen
> Sent: 23 June 2021 13:18
> 
> these are some good points.
> 
> On 23.06.21 00:18, David Laight wrote:
> > Are you saying that my 15 year old 64bit Athlon cpu and bios
> > have this large SPI flash
> 
> No. The reads will wrap, i.e. if your flash is 2MB then it would be
> repeated 8 times in the 16MB window.
> 
> > and the required hardware to
> > convert bus cycles to serial spi reads?
> 
> Yes. The window is part of the DMI interface and the south bridge or PCH
> converts the bus cycles to SPI reads. It is because this region contains
> the reset vector address of your CPU and the very first instruction it
> executes after a reset when the internal setup is done will actually be
> loaded from the serial SPI bus. It is AFAIK part of AMD's original
> 64-bit specification.
> 
> However, after reading your mail I understand that I should have looked
> up the exact explanations in the respective specs. So to definitively
> answer your question I need to know which south bridge there is in your
> 15 year old system and have a look into its datasheet. Do you know which
> one it is by any chance?

Absolutely no idea.
That particular system doesn't actually boot any more
with either cpu I have for it plugged it.
I suspect the psu voltages are out of range and have broken it.

But that isn't the point.

	David

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