Re: [Qemu-devel] [PATCH] MIPS: Fix dmtc0 instruction

[Stefan Weil <weil@mail.berlios.de>]

Thiemo Seufer schrieb:
> I can confirm it works here as well, thank you. However, I still see
>
> QEMU hang with the debian kernel at IDE detection:
>
> [...]
> [ 2.040127] pcnet32.c:v1.34-NAPI 14.Aug.2007 tsbogend@alpha.franken.de
> [ 2.040127] pcnet32: PCnet/PCI II 79C970A at 0x1020, 52:54:00:12:34:56
> assigned IRQ 10.
> [ 2.040127] eth0: registered as PCnet/PCI II 79C970A
> [ 2.040127] pcnet32: 1 cards_found.
> [ 2.040127] Uniform Multi-Platform E-IDE driver
> [ 2.040127] ide: Assuming 33MHz system bus speed for PIO modes;
> override with idebus=xx
> [ 2.040127] PIIX4: IDE controller (0x8086:0x7111 rev 0x00) at PCI slot
> 0000:00:0a.1
> [ 2.040127] PCI: Enabling device 0000:00:0a.1 (0000 -> 0001)
> [ 2.040127] PIIX4: not 100% native mode: will probe irqs later
> [ 2.040127] ide0: BM-DMA at 0x1040-0x1047, BIOS settings: hda:PIO, hdb:PIO
> [ 2.040127] ide1: BM-DMA at 0x1048-0x104f, BIOS settings: hdc:PIO, hdd:PIO
>
> I figure CONFIG_NO_HZ has too high demands on the count/compare emulation.
>
>
> Thiemo
There is a problem with the current count/compare emulation:
c0_compare_int_usable in newer Linux kernels fails to detect that it is
usable.

I had a Mips Linux kernel hanging while calibrating bogo mips caused by
this.
A workaround was running Qemu with all debug output enabled (-d ...),
so a slower running Qemu was better.

A crude workaround is here:
http://svn.berlios.de/svnroot/repos/ar7-firmware/qemu/trunk/hw/mips_timer.c

I don't really like my patch, but it improves count/compare emulation, and
my kernel no longer hangs when running in Qemu. Maybe you can try it
with your kernel.

Stefan