Re: Deprecate the ppc405 boards in QEMU?

[Thomas Huth]

On 05/10/2021 14.17, BALATON Zoltan wrote:
> On Tue, 5 Oct 2021, Thomas Huth wrote:
> > On 05/10/2021 10.07, Thomas Huth wrote:
> > > On 05/10/2021 10.05, Alexey Kardashevskiy wrote:
> > [...]
> > > > What is so special about taihu?
> > >
> > > taihu is the other 405 board defined in hw/ppc/ppc405_boards.c (which I 
> > > suggested to deprecate now)
> >
> > I've now also played with the u-boot sources a little bit, and with some 
> > bit of tweaking, it's indeed possible to compile the old taihu board 
> > there. However, it does not really work with QEMU anymore, it immediately 
> > triggers an assert():
> >
> > $ qemu-system-ppc -M taihu -bios u-boot.bin -serial null -serial mon:stdio
> > **
> > ERROR:accel/tcg/tcg-accel-ops.c:79:tcg_handle_interrupt: assertion failed: 
> > (qemu_mutex_iothread_locked())
> > Aborted (core dumped)
>
> Maybe it's similar to this: 2025fc6766ab25501e0041c564c44bb0f7389774 The 
> helper_load_dcr() and helper_store_dcr() in target/ppc/timebase_helper.c 
> seem to lock/unlock the iothread but I'm not sure if that's necessary. Also 
> not sure why this does not happen with 460ex but that maybe uses different 
> code.

It's rather the other way round, the locking is missing here instead. I can 
get the serial output with the current QEMU when I add the following patch 
(not sure whether that's the right spot, though):

diff --git a/hw/ppc/ppc.c b/hw/ppc/ppc.c
index f5d012f860..bb57f1c9ed 100644
--- a/hw/ppc/ppc.c
+++ b/hw/ppc/ppc.c
@@ -336,6 +336,8 @@ void store_40x_dbcr0(CPUPPCState *env, uint32_t val)
 {
     PowerPCCPU *cpu = env_archcpu(env);

+    qemu_mutex_lock_iothread();
+
     switch ((val >> 28) & 0x3) {
     case 0x0:
         /* No action */
@@ -353,6 +355,8 @@ void store_40x_dbcr0(CPUPPCState *env, uint32_t val)
         ppc40x_system_reset(cpu);
         break;
     }
+
+    qemu_mutex_unlock_iothread();
 }

 /* PowerPC 40x internal IRQ controller */


> > Going back to QEMU v2.3.0, I can see at least a little bit of output, but 
> > it then also triggers an assert() during DRAM initialization:
> >
> > $ qemu-system-ppc -M taihu -bios u-boot.bin -serial null -serial mon:stdio
> >
> > Reset PowerPC core
> >
> > U-Boot 2014.10-rc2-00123-g461be2f96e-dirty (Oct 05 2021 - 10:02:56)
> >
> > CPU:   AMCC PowerPC 405EP Rev. B at 770 MHz (PLB=256 OPB=128 EBC=128)
> >       I2C boot EEPROM disabled
> >       Internal PCI arbiter enabled
> >       16 KiB I-Cache 16 KiB D-Cache
> > Board: Taihu - AMCC PPC405EP Evaluation Board
> > I2C:   ready
> > DRAM:  qemu-system-ppc: memory.c:1693: memory_region_del_subregion: 
> > Assertion `subregion->container == mr' failed.
> > Aborted (core dumped)
> >
> > Not sure if this ever worked in QEMU, maybe in the early 0.15 time, but 
> > that version of QEMU also does not compile easily anymore on modern 
> > systems. So I'm afraid, getting this into a workable shape again will take 
> > a lot of time. At least I'll stop my efforts here now.
>
> Do you have this u-boot binary somewhere just for others who want to try it?

FWIW:
http://people.redhat.com/~thuth/data/u-boot-taihu.bin

 Thomas