linux-kernel - Re: [PATCH v4] powerpc: Use shared font data

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Message-ID: <20108eef-b7cf-3f23-264a-5d97021f9ffa@linux-m68k.org>
Date: Mon, 3 Nov 2025 12:33:22 +1100 (AEDT)
From: Finn Thain <fthain@...ux-m68k.org>
To: "Dr. David Alan Gilbert" <linux@...blig.org>
cc: Stan Johnson <userm57@...oo.com>, mpe@...erman.id.au, npiggin@...il.com, 
    christophe.leroy@...roup.eu, sam@...nborg.org, benh@...nel.crashing.org, 
    linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, 
    rdunlap@...radead.org, Cedar Maxwell <cedarmaxwell@....com>
Subject: Re: [PATCH v4] powerpc: Use shared font data

On Sun, 2 Nov 2025, Dr. David Alan Gilbert wrote:

> 
> So I'm not a PPC person specifically; so lets see if the PPC people have 
> any suggestions, but:
> 
>    a) Do you know if there's any way to recreate the same hang/works 
> combination in qemu; I know it has a g3beige model but I don't know how 
> to get something similar to your failing combo.
> 

I guess we could probably reproduce this in QEMU if the BootX bootloader 
could be made to work there. In theory, 'qemu-system-ppc -M g3beige' might 
work.

>    b) Can you get any diagnostics out of the prom on the mac?  Like a PC 
> or anything to have some idea where it hung?
> 

Well, that's the problem: if you enable the CONFIG_BOOTX_TEXT diagnostics, 
the system hangs instead of printing stuff. If you disable the 
CONFIG_BOOTX_TEXT diagnostics (in favour of serial diagnostics) the hang 
goes away.

Anyway, I imagine that the problem with your patch was that it relies on 
font data from a different (read only) section, which is unavailable for 
some reason (MMU not fully configured yet?)

So I've asked Stan to test a patch that simply removes the relevant 
'const' keywords. It's not a solution, but might narrow-down the search.

>    c) Is this only the Powerbooks that are unhappy - are other Macs OK 
> with this - if so, wth is the difference with a powerbook?  Is it a 
> different debian config or something?
> 

The BootX bootloader doesn't work on New World systems, which is probably 
why we don't see this regression on anything newer than a Wallstreet. 

It's likely that other Old World systems are also affected, if they are 
using BootX. We don't yet know whether the regression also affects Old 
World systems using the iQUIK bootloader instead of BootX.