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Re (early con): Re: [PATCH] Impact video driver for SGI Indigo2

To: Joshua Kinard <kumba@gentoo.org>
Subject: Re (early con): Re: [PATCH] Impact video driver for SGI Indigo2
From: peter fuerst <post@pfrst.de>
Date: Tue, 13 Sep 2011 22:27:00 +0200 (CEST)
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org, attilio.fiandrotti@gmail.com
In-reply-to: <4E6F4FFB.7050704@gentoo.org>
References: <Pine.LNX.4.64.1109111200400.4146@Indigo2.Peter> <4E6F4FFB.7050704@gentoo.org>
Reply-to: post@pfrst.de
Sender: linux-mips-bounce@linux-mips.org


Hello,

On Tue, 13 Sep 2011, Joshua Kinard wrote:

Date: Tue, 13 Sep 2011 08:43:39 -0400
From: Joshua Kinard <kumba@gentoo.org>
To: post@pfrst.de
Cc: linux-mips@linux-mips.org, ralf@linux-mips.org,
    attilio.fiandrotti@gmail.com
Subject: Re: [PATCH] Impact video driver for SGI Indigo2

On 09/11/2011 07:14, peter fuerst wrote:

+#ifndef CONFIG_EARLY_PRINTK
+        if (ctype && strstr(ctype, "impact=early"))
+#endif
+                       setup_impact_earlycons();


I think we can gut all the Impact early printk stuff.  Per Skylark, to use
it, you have to drop a function call into arch/mips/kernel/setup.c and
kernel/printk.c,

It's the setup_impact_earlycons() call in ip22-setup.c above. In so far the
patch is complete, one can leave setup.c and printk.c alone.

Depending on the situation, ip22-setup.c may not be early enough. The
setup_impact_earlycons-call could be moved near to the beginning of
start_kernel() (init/main.c), it doesn't depend on non-static kernel setup.
But this had to be done by hand, it won't be in the regular source.
So, given the intended purpose of the early console - providing helpfull
information simply by a boot option to a potential bug report by an user,
who has no inclination to kernel hacking, just wants to use the kernel out
of the box - early console may or may not be usefull.

                 so I don't think this is an easily-used feature.  In my
patchset for Gentoo's mips-sources, I actually broke both Impact and
Odyssey's early console bits out as separate drivers applied as patches if
one forces a debug mode on.

Do you intend to submit these drivers?  Anyway i will separate the early
console stuff from the "basic" Impact-patch, when i resubmit the patches,
so it's optional and can be discussed independently.

                             Because they're not really even real
consoles....just a way to get output out of offbeat systems like Octane,
which hides all the good stuff behind the broken (horifically broken) IOC3
metadevice.

Unless you've come up with a better way to do early printk that can work
shortly after the CPUs are brought up?

No regular/every-day usable method, only debug-hackery:
Moving the setup_impact_earlycons-call to start_kernel() or using a specially
tailored ARCS-console, which in addition allows to capture kernel output via
serial line (and helped me debugging for long).
(BTW: in recent kernels any ARCS-console must be switched off very early,
while in e.g. 2.6.14 it could be used until Impact or IP22Zilog take over)



...


--
Joshua Kinard
Gentoo/MIPS
kumba@gentoo.org
4096R/D25D95E3 2011-03-28

"The past tempts us, the present confuses us, the future frightens us.  And
our lives slip away, moment by moment, lost in that vast, terrible in-between."

--Emperor Turhan, Centauri Republic



kind regards

peter


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