On 2/12/19 5:51 PM, Mark Cave-Ayland wrote: > On 12/02/2019 11:03, BALATON Zoltan wrote: > >> On Tue, 12 Feb 2019, Mark Cave-Ayland wrote: >>> On 11/02/2019 23:35, Philippe Mathieu-Daudé wrote: >>> >>>> Hi Mark, >>>> >>>> On 2/10/19 6:44 PM, Mark Cave-Ayland wrote: >>>>> In order to handle a race condition in MacOS 9, a delay was introduced >>>>> when >>>>> raising the VIA SR interrupt inspired by similar code in MacOnLinux. >>>>> >>>>> During original testing of the MacOS 9 patches it was found that the 30us >>>>> delay used in MacOnLinux did not work reliably within QEMU, and a value of >>>>> 300us was required to function correctly. >>>>> >>>>> Recent experiments have shown that the previous reliability issues are no >>>>> longer present, and this value can be reduced down to 20us with no >>>>> apparent >>>>> ill effects in my local tests. This has the benefit of considerably >>>>> improving >>>>> the responsiveness of the ADB keyboard and mouse with the guest. >>>>> >>>>> Signed-off-by: Mark Cave-Ayland <[email protected]> >>>>> --- >>>>> hw/misc/macio/cuda.c | 11 +---------- >>>>> 1 file changed, 1 insertion(+), 10 deletions(-) >>>>> >>>>> diff --git a/hw/misc/macio/cuda.c b/hw/misc/macio/cuda.c >>>>> index c4f7a2f39b..3febacdd1e 100644 >>>>> --- a/hw/misc/macio/cuda.c >>>>> +++ b/hw/misc/macio/cuda.c >>>>> @@ -97,17 +97,8 @@ static void cuda_set_sr_int(void *opaque) >>>>> >>>>> static void cuda_delay_set_sr_int(CUDAState *s) >>>>> { >>>>> - MOS6522CUDAState *mcs = &s->mos6522_cuda; >>>>> - MOS6522State *ms = MOS6522(mcs); >>>>> - MOS6522DeviceClass *mdc = MOS6522_DEVICE_GET_CLASS(ms); >>>>> int64_t expire; >>>>> >>>>> - if (ms->dirb == 0xff || s->sr_delay_ns == 0) { >>>>> - /* Disabled or not in Mac OS, fire the IRQ directly */ >>>>> - mdc->set_sr_int(ms); >>>>> - return; >>>>> - } >>>> >>>> The change of sr_delay_ns below is well explained, but I don't >>>> understand why you remove the previous if(). >>> >>> IIRC it was a hack by Alex to try and restrict the delay on the interrupt >>> just to >>> MacOS instead of Linux, but with the reduced value it doesn't really matter >>> any more. >> >> If this delay is to prevent a bug which only happens in MacOS then that's >> the hack >> not the normal code path to run without the delay that you've just removed. >> So maybe >> this should be kept if possible to avoid unecessary delays for other guests. >> (Although if this only affects mac99,via=cuda but not mac99,via=pmu then I >> don't care >> much as long as pmu works.) > > Well the reality is that the detection above doesn't actually seem to work > anyway - > at least a quick boot test with Linux, MacOS X and MacOS 9 with a printf() > added into > the if() shows nothing firing once the kernel takes over. So the slow path > with the > delay included was always being taken within the OS anyway. > > And indeed, the code doesn't affect pmu so you won't see any difference there. > >>> As a plus it also prevents a guest OS from accidentally triggering the hack >>> whilst >>> programming the VIA port. >> >> That may be a problem though. What's the issue exactly? Why is the delay >> needed in >> the first place? > > It's some kind of racy polling with OS 9 (I wasn't involved in the technical > details, > sorry) which causes OS 9 to hang on boot if the delay isn't present. And even > better > the slow path that was previously always being taken has now been reduced > from 300us > to 30us so whichever way you look at it, having this patch applied is a win.
Can you write a paragraph about this, that David can amend to your patch? That would stop worrying me about looking at this patch in various months... Thanks! Phil.
