Re: [Qemu-devel] [PATCH target-arm v5 4/5] arm: Implement reset GPIO.

[Peter Maydell]

On 15 January 2014 09:14, Peter Crosthwaite
<address@hidden> wrote:
> Implement a reset GPIO for ARM CPUs. This allows individual reset of ARM
> CPUs from device land without the need for the much unwanted reset API
> calls.
>
> The CPU is halted as long as the pin is held in reset. Releasing the
> reset starts the CPU running again.

> +static void arm_cpu_reset_gpio(void *opaque, int irq, int level)
> +{
> +    CPUState *cpu = opaque;
> +
> +    if (level) {
> +        cpu_reset(cpu);
> +        cpu_interrupt(cpu, CPU_INTERRUPT_HALT);
> +    } else {
> +        cpu_reset_interrupt(cpu, CPU_INTERRUPT_HALT);
> +        cpu_interrupt(cpu, CPU_INTERRUPT_EXITTB);
> +    }
> +}

I don't think this will work properly. For instance,
cpu_exec() will bring the CPU out of halt if an inbound
interrupt arrives, but we should stay in reset until
the reset line is deasserted.

Also ideally speaking we should probably do the reset
actions on the falling edge of reset, not the rising edge.

Does this work properly when we're running under KVM
rather than using the TCG CPU?

Is there anything really ARM-specific in this reset_gpio
function, or could it be implemented at a common level for
all target architectures?

> -/* Meanings of the ARMCPU object's two inbound GPIO lines */
> -#define ARM_CPU_IRQ 0
> -#define ARM_CPU_FIQ 1
> +/* Meanings of the ARMCPU object's inbound GPIO lines.  */
> +#define ARM_CPU_IRQ         0
> +#define ARM_CPU_FIQ         1
> +/* reset GPIO is inited after irqs, so its index is one past FIQ */
> +#define ARM_CPU_RESET       (ARM_CPU_FIQ + 1)

ARMv8 also has an SError which probably ought to follow IRQ/FIQ,
but I think we can safely renumber GPIO lines without breaking
migration.

thanks
-- PMM