Re: [Qemu-devel] [PATCH] cuda: decrease time delay before raising VIA SR interrupt

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

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 <mark.cave-ayland@ilande.co.uk>
>> ---
>>  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.
As a plus it also prevents a guest OS from accidentally triggering the hack whilst
programming the VIA port.


ATB,

Mark.