linux-kernel - Re: [PATCH] Open Firmware device tree virtual filesystem

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Date:	Wed, 3 Jan 2007 16:31:45 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, devel@...top.org,
	jengelh@...ux01.gwdg.de, benh@...nel.crashing.org,
	wmb@...mworks.com, jg@...top.org
Subject: Re: [PATCH] Open Firmware device tree virtual filesystem

>> Kill OF? sparc does not want that IMO, how else should I return to
>> the 'ok' prompt?
>
> PowerPC kills OF because it really has to,

No it doesn't.  It has to on some (very common, heh) subarchs.

> that's one of numerous
> reasons that it started sucking the device tree into a kernel copy
> early in the bootup and using that for device discovery etc.
>
> To be honest, the 'ok' prompt is of limited value when you have
> things like Alt-SysRq and PPC's XMON debugger in the kernel already.

When I ported the PowerPC kernel to a new platform years ago,
the big problems happened *before* any of those methods worked,
at really early boot time (the PowerPC port has become a lot
better since then fwiw, it might be easier now).  Running (and
debugging) other client programs was a lot easier, since you
could always drop back to OF on panic conditions so you could
investigate what was going on without using hardware probes.

> In fact, the 'ok' prompt is an ENORMOUS pain in the ass to support
> on machines with USB keyboards, because sharing the USB host
> controller is beyond non-trivial.  I've never implemented support
> for that on sparc64 and I frankly have no desire to do the work
> necessary to support that.  It simply is not worth it.

Oh yes, USB keyboards, lovely.  Use a serial port, or a dedicated
network controller, or similar, for the OF console instead ;-)

Segher

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