Re: [Qemu-devel] [PATCH KVM v2 2/4] KVM: additional i8254 output fixes

[Gleb Natapov <gleb@redhat.com>]

On Wed, Dec 26, 2012 at 10:39:54PM -0700, Matthew Ogilvie wrote:
> Make git_get_out() consistent with spec.  Currently pit_get_out()
> doesn't affect IRQ0, but it can be read by the guest in other ways.
> This makes it consistent with proposed changes in qemu's i8254 model
> as well.
> 
> See http://bochs.sourceforge.net/techspec/intel-82c54-timer.pdf.gz
> or search the net for 23124406.pdf.
> 
> Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
> ---
>  arch/x86/kvm/i8254.c | 44 ++++++++++++++++++++++++++++++++++----------
>  1 file changed, 34 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
> index cd4ec60..fd38938 100644
> --- a/arch/x86/kvm/i8254.c
> +++ b/arch/x86/kvm/i8254.c
> @@ -144,6 +144,10 @@ static int pit_get_count(struct kvm *kvm, int channel)
>  
>  	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
>  
> +	/* FIXME: Add some way to represent a paused timer and return
> +	 *   the paused-at counter value, to better model gate pausing,
> +	 *   "wait until next CLK pulse to load counter" logic, etc.
> +	 */
>  	t = kpit_elapsed(kvm, c, channel);
>  	d = muldiv64(t, KVM_PIT_FREQ, NSEC_PER_SEC);
>  
> @@ -155,8 +159,7 @@ static int pit_get_count(struct kvm *kvm, int channel)
>  		counter = (c->count - d) & 0xffff;
>  		break;
>  	case 3:
> -		/* XXX: may be incorrect for odd counts */
> -		counter = c->count - (mod_64((2 * d), c->count));
> +		counter = (c->count - (mod_64((2 * d), c->count))) & 0xfffe;
>  		break;
>  	default:
>  		counter = c->count - mod_64(d, c->count);
> @@ -180,20 +183,18 @@ static int pit_get_out(struct kvm *kvm, int channel)
>  	switch (c->mode) {
>  	default:
>  	case 0:
> -		out = (d >= c->count);
> -		break;
>  	case 1:
> -		out = (d < c->count);
> +		out = (d >= c->count);
>  		break;
>  	case 2:
> -		out = ((mod_64(d, c->count) == 0) && (d != 0));
> +		out = (mod_64(d, c->count) != (c->count - 1) || c->gate == 0);
>  		break;
>  	case 3:
> -		out = (mod_64(d, c->count) < ((c->count + 1) >> 1));
> +		out = (mod_64(d, c->count) < ((c->count + 1) >> 1) || c->gate == 0);
>  		break;
>  	case 4:
>  	case 5:
> -		out = (d == c->count);
> +		out = (d != c->count);
>  		break;
>  	}
>  
> @@ -367,7 +368,7 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
>  
>  	/*
>  	 * The largest possible initial count is 0; this is equivalent
> -	 * to 216 for binary counting and 104 for BCD counting.
> +	 * to pow(2,16) for binary counting and pow(10,4) for BCD counting.
>  	 */
>  	if (val == 0)
>  		val = 0x10000;
> @@ -376,6 +377,26 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
>  
>  	if (channel != 0) {
>  		ps->channels[channel].count_load_time = ktime_get();
> +
> +		/* In gate-triggered one-shot modes,
> +		 * indirectly model some pit_get_out()
> +		 * cases by setting the load time way
> +		 * back until gate-triggered.
> +		 * (Generally only affects reading status
> +		 * from channel 2 speaker,
> +		 * due to hard-wired gates on other
> +		 * channels.)
> +		 *
> +		 * FIXME: This might be redesigned if a paused
> +		 * timer state is added for pit_get_count().
> +		 */
> +		if (ps->channels[channel].mode == 1 ||
> +		    ps->channels[channel].mode == 5) {
> +	            u64 delta = muldiv64(val+2, NSEC_PER_SEC, KVM_PIT_FREQ);
> +		    ps->channels[channel].count_load_time =
> +                            ktime_sub(ps->channels[channel].count_load_time,
> +                                      ns_to_ktime(delta));
I do not understand what are you trying to do here. You assume that
trigger will happen 2 clocks after counter is loaded?

> +		}
>  		return;
>  	}
>  
> @@ -383,7 +404,6 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
>  	 * mode 1 is one shot, mode 2 is period, otherwise del timer */
>  	switch (ps->channels[0].mode) {
>  	case 0:
> -	case 1:
>          /* FIXME: enhance mode 4 precision */
>  	case 4:
>  		create_pit_timer(kvm, val, 0);
> @@ -393,6 +413,10 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
>  		create_pit_timer(kvm, val, 1);
>  		break;
>  	default:
> +		/* Modes 1 and 5 are triggered by gate leading edge,
> +		 * but channel 0's gate is hard-wired high and has
> +		 * no edges (on normal real hardware).
> +		 */
>  		destroy_pit_timer(kvm->arch.vpit);
>  	}
>  }
> -- 
> 1.7.10.2.484.gcd07cc5

--
			Gleb.