Subject: Re: [PATCH v5 1/5] powerpc/85xx: implement hardware timebase sync

From: Scott Wood <[email-masked]>
Date: Fri, 1 Jun 2012 10:40:00 -0500

On 05/11/2012 06:53 AM, Zhao Chenhui wrote:
>  #ifdef CONFIG_KEXEC
> +static struct ccsr_guts __iomem *guts;
> +static u64 timebase;
> +static int tb_req;
> +static int tb_valid;
> +
> +static void mpc85xx_timebase_freeze(int freeze)

Why is this under CONFIG_KEXEC?  It'll also be needed for CPU hotplug.

> +{
> +	unsigned int mask;
> +
> +	if (!guts)
> +		return;
> +
> +	mask = CCSR_GUTS_DEVDISR_TB0 | CCSR_GUTS_DEVDISR_TB1;
> +	if (freeze)
> +		setbits32(&guts->devdisr, mask);
> +	else
> +		clrbits32(&guts->devdisr, mask);
> +
> +	in_be32(&guts->devdisr);
> +}
> +
> +static void mpc85xx_give_timebase(void)
> +{
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +
> +	while (!tb_req)
> +		barrier();
> +	tb_req = 0;
> +
> +	mpc85xx_timebase_freeze(1);
> +	timebase = get_tb();
> +	mb();
> +	tb_valid = 1;
> +
> +	while (tb_valid)
> +		barrier();
> +
> +	mpc85xx_timebase_freeze(0);
> +
> +	local_irq_restore(flags);
> +}
> +
> +static void mpc85xx_take_timebase(void)
> +{
> +	unsigned long flags;
> +
> +	local_irq_save(flags);
> +
> +	tb_req = 1;
> +	while (!tb_valid)
> +		barrier();
> +
> +	set_tb(timebase >> 32, timebase & 0xffffffff);
> +	mb();
> +	tb_valid = 0;
> +
> +	local_irq_restore(flags);
> +}

I know you say this is for dual-core chips only, but it would be nice if
you'd write this in a way that doesn't assume that (even if the
corenet-specific timebase freezing comes later).

Do we need an isync after setting the timebase, to ensure it's happened
before we enable the timebase?  Likewise, do we need a readback after
disabling the timebase to ensure it's disabled before we read the
timebase in give_timebase?

>  atomic_t kexec_down_cpus = ATOMIC_INIT(0);
>  
>  void mpc85xx_smp_kexec_cpu_down(int crash_shutdown, int secondary)
> @@ -228,6 +286,20 @@ smp_85xx_setup_cpu(int cpu_nr)
>  		doorbell_setup_this_cpu();
>  }
>  
> +#ifdef CONFIG_KEXEC
> +static const struct of_device_id guts_ids[] = {
> +	{ .compatible = "fsl,mpc8572-guts", },
> +	{ .compatible = "fsl,mpc8560-guts", },
> +	{ .compatible = "fsl,mpc8536-guts", },
> +	{ .compatible = "fsl,p1020-guts", },
> +	{ .compatible = "fsl,p1021-guts", },
> +	{ .compatible = "fsl,p1022-guts", },
> +	{ .compatible = "fsl,p1023-guts", },
> +	{ .compatible = "fsl,p2020-guts", },
> +	{},
> +};
> +#endif

MPC8560 and MPC8536 are single-core...

Also please use a more specific name, such as e500v2_smp_guts_ids or
mpc85xx_smp_guts_ids -- when corenet support is added it will likely be
in the same file.

>  void __init mpc85xx_smp_init(void)
>  {
>  	struct device_node *np;
> @@ -249,6 +321,19 @@ void __init mpc85xx_smp_init(void)
>  		smp_85xx_ops.cause_ipi = doorbell_cause_ipi;
>  	}
>  
> +#ifdef CONFIG_KEXEC
> +	np = of_find_matching_node(NULL, guts_ids);
> +	if (np) {
> +		guts = of_iomap(np, 0);
> +		smp_85xx_ops.give_timebase = mpc85xx_give_timebase;
> +		smp_85xx_ops.take_timebase = mpc85xx_take_timebase;
> +		of_node_put(np);
> +	} else {
> +		smp_85xx_ops.give_timebase = smp_generic_give_timebase;
> +		smp_85xx_ops.take_timebase = smp_generic_take_timebase;
> +	}

Do not use smp_generic_give/take_timebase, ever.  If you don't have the
guts node, then just assume the timebase is already synced.

-Scott