Re: [XEN v1] xen: arm: Check if timer is enabled for timer irq

[Ayan Kumar Halder <ayankuma@xxxxxxx>]

On 10/08/2022 13:16, Bertrand Marquis wrote:
> Hi Ayan,
Hi Bertrand,

> > On 10 Aug 2022, at 11:58, Ayan Kumar Halder <ayankuma@xxxxxxx> wrote:
> >
> > Refer "Arm Architecture Registers DDI 0595", AArch32 system registers,
> > CNTHP_CTL :- "When the value of the ENABLE bit is 1, ISTATUS indicates
> > whether the timer condition is met."
> >
> > Also similar description applies to CNTP_CTL as well.
> >
> > One should always check that the timer is enabled and status is set, to
> > determine if the timer interrupt has been generated.
> >
> > Signed-off-by: Ayan Kumar Halder <ayankuma@xxxxxxx>
> > ---
> > xen/arch/arm/time.c | 12 ++++++++----
> > 1 file changed, 8 insertions(+), 4 deletions(-)
> >
> > diff --git a/xen/arch/arm/time.c b/xen/arch/arm/time.c
> > index dec53b5f7d..f220586c52 100644
> > --- a/xen/arch/arm/time.c
> > +++ b/xen/arch/arm/time.c
> > @@ -222,8 +222,13 @@ int reprogram_timer(s_time_t timeout)
> > /* Handle the firing timer */
> > static void timer_interrupt(int irq, void *dev_id, struct cpu_user_regs *regs)
> > {
> > -    if ( irq == (timer_irq[TIMER_HYP_PPI]) &&
> > -         READ_SYSREG(CNTHP_CTL_EL2) & CNTx_CTL_PENDING )
> > +    uint8_t timer_en_mask = (CNTx_CTL_PENDING | CNTx_CTL_ENABLE);
> This should either be a macro or be added directly into the condition.
>
> But here seeing the rest of the code, I would suggest to create a macro for the
> whole condition and use it directly into the ifs as I find that this solution 
> using
> boolean variable is making the code unclear.
>
> May I suggest the following:
> #define CNTx_CTL_IS_PENDING(reg) (READ_SYSREG(reg) & (CNTx_CTL_PENDING | 
> CNTx_CTL_ENABLE))
This will return true even if either CNTx_CTL_PENDING or CNTx_CTL_ENABLE 
is set.
> Or in fact just adding CNTx_CTL_ENABLE in the if directly.
We want to check that both are set.

So this should be :-
#define CNTx_CTL_IS_PENDING(reg) ( (READ_SYSREG(reg) & (CNTx_CTL_PENDING | 
CNTx_CTL_ENABLE)) ==
(CNTx_CTL_PENDING | CNTx_CTL_ENABLE) )

Let me know if you agree. I will prefer using a macro rather putting this in 
'if' condition as it might make readability difficult.

- Ayan
 

> > +    bool timer_cond_el2 = (READ_SYSREG(CNTHP_CTL_EL2) & timer_en_mask) ==
> > +        timer_en_mask ? true : false;
> ? True:false is redundant here and not needed.
>
> > +    bool timer_cond_el0 = (READ_SYSREG(CNTP_CTL_EL0) & timer_en_mask) ==
> > +        timer_en_mask ? true : false;
> Same here
>
> > +
> > +    if ( irq == (timer_irq[TIMER_HYP_PPI]) && timer_cond_el2 )
> >      {
> >          perfc_incr(hyp_timer_irqs);
> >          /* Signal the generic timer code to do its work */
> > @@ -232,8 +237,7 @@ static void timer_interrupt(int irq, void *dev_id, struct 
> > cpu_user_regs *regs)
> >          WRITE_SYSREG(0, CNTHP_CTL_EL2);
> >      }
> >
> > -    if ( irq == (timer_irq[TIMER_PHYS_NONSECURE_PPI]) &&
> > -         READ_SYSREG(CNTP_CTL_EL0) & CNTx_CTL_PENDING )
> > +    if ( irq == (timer_irq[TIMER_PHYS_NONSECURE_PPI]) && timer_cond_el0 )
> >      {
> >          perfc_incr(phys_timer_irqs);
> >          /* Signal the generic timer code to do its work */
> > --
> > 2.17.1
> Cheers
> Bertrand