Re: [PATCH 1/5] hw/ppc/spapr_iommu: Register machine reset handler

[Greg Kurz]

On Tue, 27 Apr 2021 11:20:07 +0200
Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:

> On 4/27/21 3:45 AM, David Gibson wrote:
> > On Sat, Apr 24, 2021 at 06:22:25PM +0200, Philippe Mathieu-Daudé wrote:
> >> The TYPE_SPAPR_TCE_TABLE device is bus-less, thus isn't reset
> >> automatically.  Register a reset handler to get reset with the
> >> machine.
> >>
> >> It doesn't seem to be an issue because it is that way since the
> >> device QDev'ifycation 8 years ago, in commit a83000f5e3f
> >> ("spapr-tce: make sPAPRTCETable a proper device").
> >> Still, correct to have a proper API usage.
> > 
> > So, the reason this works now is that we explicitly call
> > device_reset() on the TCE table from the TCE tables "owner", either a
> > PHB (spapr_phb_reset()) or a VIO device (spapr_vio_quiesce_one()).
> > 
> > I think we want either that, or the register_reset(), not both.
> 
> rtas_quiesce() seems to call a DeviceClass::reset() on the
> children of TYPE_SPAPR_VIO_BUS:
> 
> Abstract TYPE_VIO_SPAPR_DEVICE has the TYPE_SPAPR_VIO_BUS bus_type,
> and registers the spapr_vio_busdev_reset() handler, which calls
> spapr_vio_quiesce_one()...
> 
> So either we already have 2 resets, or the bus is never reset?
> 

rtas_quiesce() is called when the guests definitively transition
from the SLOF FW to the OS. It isn't a true reset path actually,
even if it needs to reset a few devices.

On the other hand, your patch would _really_ cause the TCE table
device to be reset twice at machine reset AFAICT.

> The bus is created in spapr_machine_init():
> 
>     /* Set up VIO bus */
>     spapr->vio_bus = spapr_vio_bus_init();
> 
> TYPE_SPAPR_MACHINE class registers spapr_machine_reset(), which
> manually calls qemu_devices_reset() and spapr_drc_reset_all(),
> but I can't understand if a callee resets vio_bus...

The vio_bus *is* reset:

#0  0x0000000100629a98 in spapr_vio_busdev_reset (qdev=0x10165c400) at 
/home/greg/Work/qemu/qemu-virtiofs/include/hw/ppc/spapr_vio.h:31
#1  0x00000001009fd32c in device_transitional_reset (obj=0x10165c400) at 
/home/greg/Work/qemu/qemu-virtiofs/include/hw/qdev-core.h:17
#2  0x0000000100a00e24 in resettable_phase_hold (obj=0x10165c400, 
opaque=<optimized out>, type=<optimized out>) at ../../hw/core/resettable.c:182
#3  0x00000001009f9108 in bus_reset_child_foreach (obj=<optimized out>, 
cb=0x100a00cc0 <resettable_phase_hold>, opaque=0x0, type=<optimized out>) at 
../../hw/core/bus.c:97
#4  0x0000000100a00db8 in resettable_child_foreach (rc=0x1014f5400, 
type=RESET_TYPE_COLD, opaque=0x0, cb=0x100a00cc0 <resettable_phase_hold>, 
obj=0x10156e600) at ../../hw/core/resettable.c:96
#5  0x0000000100a00db8 in resettable_phase_hold (obj=0x10156e600, 
opaque=<optimized out>, type=<optimized out>) at ../../hw/core/resettable.c:173
#6  0x00000001009fcaa8 in device_reset_child_foreach (obj=<optimized out>, 
cb=0x100a00cc0 <resettable_phase_hold>, opaque=0x0, type=<optimized out>) at 
../../hw/core/qdev.c:366
#7  0x0000000100a00db8 in resettable_child_foreach (rc=0x1013eef90, 
type=RESET_TYPE_COLD, opaque=0x0, cb=0x100a00cc0 <resettable_phase_hold>, 
obj=0x10164a0e0) at ../../hw/core/resettable.c:96
#8  0x0000000100a00db8 in resettable_phase_hold (obj=0x10164a0e0, 
opaque=<optimized out>, type=<optimized out>) at ../../hw/core/resettable.c:173
#9  0x00000001009f9108 in bus_reset_child_foreach (obj=<optimized out>, 
cb=0x100a00cc0 <resettable_phase_hold>, opaque=0x0, type=<optimized out>) at 
../../hw/core/bus.c:97
#10 0x0000000100a00db8 in resettable_child_foreach (rc=0x1012b1a00, 
type=RESET_TYPE_COLD, opaque=0x0, cb=0x100a00cc0 <resettable_phase_hold>, 
obj=0x10154d4b0) at ../../hw/core/resettable.c:96
#11 0x0000000100a00db8 in resettable_phase_hold (obj=obj@entry=0x10154d4b0, 
opaque=opaque@entry=0x0, type=type@entry=RESET_TYPE_COLD) at 
../../hw/core/resettable.c:173
#12 0x0000000100a01794 in resettable_assert_reset (obj=0x10154d4b0, 
type=<optimized out>) at ../../hw/core/resettable.c:60
#13 0x0000000100a01c60 in resettable_reset (obj=0x10154d4b0, type=<optimized 
out>) at ../../hw/core/resettable.c:45
#14 0x0000000100a020ec in resettable_cold_reset_fn (opaque=<optimized out>) at 
../../hw/core/resettable.c:269
#15 0x0000000100a00718 in qemu_devices_reset () at ../../hw/core/reset.c:69
#16 0x0000000100624024 in spapr_machine_reset (machine=0x101545480) at 
../../hw/ppc/spapr.c:1587
#17 0x00000001007b8128 in qemu_system_reset (reason=<optimized out>) at 
../../softmmu/runstate.c:442
#18 0x00000001007b8fa8 in main_loop_should_exit () at 
../../softmmu/runstate.c:687
#19 0x00000001007b8fa8 in qemu_main_loop () at ../../softmmu/runstate.c:721
#20 0x00000001002f5150 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at ../../softmmu/main.c:50

And it seems rtas_quiesce() could just do bus_cold_reset(&bus->bus)
rather than open-coding the walk of vio_bus children.