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Re: [MIPS] 64-bit Sibyte kernels need DMA32.

Subject: Re: [MIPS] 64-bit Sibyte kernels need DMA32.
From: Atsushi Nemoto <>
Date: Fri, 28 Dec 2007 01:43:21 +0900 (JST)
In-reply-to: <S20038938AbXKZMRu/>
Original-recipient: rfc822;
References: <S20038938AbXKZMRu/>
On Mon, 26 Nov 2007 12:17:46 +0000, wrote:
> Author: Ralf Baechle <> Sat Nov 3 02:05:43 2007 +0000
> Commit: 75c0de3513644f9868a14f74b0c4dfec1eb4ffd5
> Gitweb:
> Branch: master
> Sibyte SOCs only have 32-bit PCI.  Due to the sparse use of the address
> space only the first 1GB of memory is mapped at physical addresses
> below 1GB.  If a system has more than 1GB of memory 32-bit DMA will
> not be able to reach all of it.
> For now this patch is good enough to keep Sibyte users happy but it seems
> eventually something like swiotlb will be needed for Sibyte.

This commit breaks platforms which have real prom_free_prom_memory().

You can reproduce the problem with this patch.

diff --git a/arch/mips/qemu/q-mem.c b/arch/mips/qemu/q-mem.c
index dae39b5..84cbee2 100644
--- a/arch/mips/qemu/q-mem.c
+++ b/arch/mips/qemu/q-mem.c
@@ -1,5 +1,9 @@
 #include <linux/init.h>
+#include <asm/bootinfo.h>
+#include <asm/sections.h>
+#include <asm/page.h>
 void __init prom_free_prom_memory(void)
+       free_init_pages("prom memory", PAGE_SIZE, __pa_symbol(&_text));

With this patch, qemu kernel crashes on boot as this:

Bad page state in process 'swapper'
page:81000020 flags:0x00000000 mapping:00000000 mapcount:1 count:0
Trying to fix it up, but a reboot is needed
Call Trace:
[<8001691c>] dump_stack+0x8/0x34
[<8005a758>] bad_page+0x6c/0xa4
[<8005af7c>] free_hot_cold_page+0x98/0x1d4
[<80019e44>] free_init_pages+0x94/0xf8
[<80164b3c>] free_initmem+0x10/0x40
[<80010428>] init_post+0x10/0xe8
[<801b988c>] kernel_init+0x2f8/0x328
[<80013220>] kernel_thread_helper+0x10/0x18

If I reverted the commit, this crash does not happen.  How I can fix this?

Atsushi Nemoto

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