From: Matt Porter <porter@cox•net>
To: Allen Curtis <acurtis@onz•com>
Cc: David Gibson <david@gibson•dropbear.id.au>,
Matt Porter <porter@cox•net>, Andrew May <acmay@acmay•homeip.net>,
linuxppc-embedded@lists•linuxppc.org
Subject: Re: very minor 405GP and 405GPr PCI difference
Date: Tue, 8 Oct 2002 08:18:00 -0700 [thread overview]
Message-ID: <20021008081800.C21266@home.com> (raw)
In-Reply-To: <NCBBIINEHIPFGJPLBEIFOEPEDMAA.acurtis@onz.com>; from acurtis@onz.com on Mon, Oct 07, 2002 at 11:19:31PM -0700
On Mon, Oct 07, 2002 at 11:19:31PM -0700, Allen Curtis wrote:
> > As Matt says, this would fall out naturally from a better control
> > structure. Howeever, I tend to think that leaving things like this to
> > the bootloader/firmware is a bad idea:
> >
> > The kernel has to know how PCI addresses are mapped anyway, so this
> > becomes yet another point at which the kernel and firmware are bound
> > together. Why should the kernel have code to deal with umpteen
> > different cases of how PCI might have been set up, or not set up by
> > the firmware/bootloader, when it can just take control of the host
> > bridge and reprogram it how it wants? Once the debugging cruft comes
> > out, it should only be a couple of hundred bytes of code.
>
> I believe that there are many cases where the kernel code is much too
> aggressive with configuration. Personally I believe that all BIOS code
> should totally initialize the processor state so you always have a known
> starting point. (whether you boot Linux or not) Many times I have had to
> track down where the kernel thinks it "knows" the proper configuration and
> unravels the work done by the BIOS. I am not sure how to solve this problem
> but I believe the kernel should attempt to detect and use a configuration
> before reconfiguring any hardware. I have implemented this technique in our
> UART and Ethernet configuration stuff on the 8260 with good success.
>
> Only a suggestion...
This is a good time to reiterate that *if* your processor family
code is designed with the proper flow, you can decide how to approach
this on a case-by-case basis.
I don't want to comment to heavily on 826x stuffs but I think the
approach may well be the by-product of Dan's methodology of a
minimal bootrom, thus necessitating chip-level setup. The
code clearly follows the "flow through a common file" approach
which tends to make per-board/system changes a bit hacky if you
start having 8260-based systems that have attributes that are
less alike. The approach is fine if every system using a particular
SoC is very similar (i.e. not much external I/O or custom strappings).
I laid out the three cases of firmware/kernel coupling that I
know of in a separate post. I think you'll find that there
are many cases where it is not feasible or possible to control
the firmware. Obviously, we would all like to have the firmware
be 100% correct but that is not reality. In some ways, you folks
doing custom board bringup for you application have the ideal
situation compared to dealing with reference/COTS boards with
blackbox firmware.
Regards,
--
Matt Porter
porter@cox•net
This is Linux Country. On a quiet night, you can hear Windows reboot.
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2002-10-08 15:18 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-09-27 12:27 very minor 405GP and 405GPr PCI difference Ralph Blach
2002-09-30 4:01 ` David Gibson
2002-10-01 5:21 ` David Gibson
2002-10-01 8:37 ` "David Müller (ELSOFT AG)"
2002-10-02 1:42 ` David Gibson
2002-10-02 4:26 ` Allen Curtis
2002-10-02 5:34 ` David Gibson
2002-10-02 17:03 ` Matt Porter
2002-10-03 1:10 ` David Gibson
2002-10-03 15:14 ` Matt Porter
2002-10-04 2:48 ` David Gibson
2002-10-04 18:33 ` Todd Poynor
2002-10-08 4:17 ` David Gibson
2002-10-08 19:39 ` Todd Poynor
2002-10-09 2:14 ` David Gibson
[not found] ` <20021 <20021023040850.GC1198@zax>
2002-10-24 23:50 ` Ralph Blach
2002-10-25 1:19 ` David Gibson
2002-10-02 7:46 ` "David Müller (ELSOFT AG)"
2002-10-03 1:12 ` David Gibson
2002-10-03 8:28 ` "David Müller (ELSOFT AG)"
2002-10-06 5:23 ` Andrew May
2002-10-07 1:31 ` Matt Porter
2002-10-08 4:14 ` David Gibson
2002-10-08 5:21 ` Andrew May
2002-10-08 14:56 ` Matt Porter
2002-10-08 17:31 ` Andrew May
2002-10-08 18:20 ` Matt Porter
2002-10-09 1:58 ` David Gibson
2002-10-09 10:35 ` Kenneth Johansson
2002-10-09 15:21 ` Allen Curtis
2002-10-11 19:37 ` Andrew May
2002-10-14 1:20 ` David Gibson
2002-10-08 6:19 ` Allen Curtis
2002-10-08 15:18 ` Matt Porter [this message]
2002-10-09 2:10 ` David Gibson
2002-10-22 21:55 ` Todd Poynor
2002-10-23 4:08 ` David Gibson
-- strict thread matches above, loose matches on Subject: below --
2002-10-23 13:10 Ralph Blach
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