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

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Ayan,

> 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))

Or in fact just adding CNTx_CTL_ENABLE in the if directly.

> +    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