From: Timur Tabi <timur@freescale.com>
To: rmcguire@videopresence.com
Cc: linuxppc-embedded@ozlabs.org
Subject: Re: DTS files, 83xx, clock frequencies
Date: Wed, 19 Dec 2007 09:14:17 -0600 [thread overview]
Message-ID: <47693549.9030105@freescale.com> (raw)
In-Reply-To: <000001c841ce$d11fcdd0$6405a8c0@absolut>
Russell McGuire wrote:
> Isn't default behavior that these fields are kept from the <BIOS> U-boot
> during boot, if a zero is present? Is there any advantage to resetting them
> within the dts file during linux boot up?
Depending on which version of U-Boot, a given property may or may not be
initialized by U-Boot. The problem is that as new properties are defined,
U-Boot is not always updated to initialize that property, and sometimes it's
only updated on some CPU families.
The qe/brg-frequency property is a good example. Prior to U-Boot 1.3, it was
not being initialized at all. With U-Boot 1.3, it's only initialized on 83xx,
even though some 85xx boards have a QE. I have a QE UART driver that looks at
qe/brg-frequency, and if it's non-zero, I use it. If it is zero, then I take
the qe/bus-frequency property and divide it in half.
--
Timur Tabi
Linux kernel developer at Freescale
prev parent reply other threads:[~2007-12-19 15:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <mailman.543.1198006353.17691.linuxppc-embedded@ozlabs.org>
2007-12-18 23:36 ` DTS files, 83xx, clock frequencies Russell McGuire
2007-12-18 23:59 ` Scott Wood
2007-12-19 15:14 ` Timur Tabi [this message]
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