Re: [Ksummit-2009-discuss] Representing Embedded Architectures at the Kernel Summit

From: Ralf Baechle <ralf@linux-mips.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Mike Frysinger <vapier.adi@gmail.com>,
	Mike Rapoport <mike@compulab.co.il>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	linux-arch@vger.kernel.org, linux-embedded@vger.kernel.org,
	ksummit-2009-discuss@lists.linux-foundation.org
Subject: Re: [Ksummit-2009-discuss] Representing Embedded Architectures at the Kernel Summit
Date: Wed, 17 Jun 2009 16:04:14 +0100	[thread overview]
Message-ID: <20090617150414.GA18525@linux-mips.org> (raw)
In-Reply-To: <4A38705A.3060007@zytor.com>

On Tue, Jun 16, 2009 at 09:26:02PM -0700, H. Peter Anvin wrote:

> > I2C or similar busses can be a particularly annoying if they contain
> > essential configuration information such as memory size which is needed
> > long before anything else.  So for far a common solution is that platforms
> > are carrying a private (aka redundant, ugly) early-i2c system that's just
> > about sufficient for this purpose.
> 
> For what it's worth, this is true for pretty much ALL systems with
> removable memory modules, since Serial Presence Detect (SPD) is
> electrically equivalent to I2C.
> 
> However, on most systems, even embedded, bringing up memory falls on
> firmware (sometimes in the form of a boot loader) so Linux rarely sees it.

There are embedded systems were the firmware does not provide a usuable
memory map or where that is plain broken.  Or Linux with some extra init
code serves as the firmware.  Often there is a single serial EEPROM for
the entire system.  If there is an atrocity that can save a penny it will
be commited at least in the embedded world.

  Ralf