[U-Boot] [PATCH v3 09/12] tegra124: Add PSCI support for Tegra124

[Thierry Reding <treding@nvidia.com>]

On Wed, Feb 18, 2015 at 09:14:03AM +0100, Jan Kiszka wrote:
[...]
> diff --git a/arch/arm/cpu/armv7/tegra124/ap.c b/arch/arm/cpu/armv7/tegra124/ap.c
[...]
> +void ap_pm_init(void)
> +{
> +	struct flow_ctlr *flow = (struct flow_ctlr *)NV_PA_FLOW_BASE;
> +	struct pmc_ctlr *pmc = (struct pmc_ctlr *)NV_PA_PMC_BASE;
> +
> +	writel((u32)park_cpu, EXCEP_VECTOR_CPU_RESET_VECTOR);
> +
> +	tegra_powergate_power_on(TEGRA_POWERGATE_CPU1);
> +	tegra_powergate_power_on(TEGRA_POWERGATE_CPU2);
> +	tegra_powergate_power_on(TEGRA_POWERGATE_CPU3);
> +
> +	writel((2 << CSR_WAIT_WFI_SHIFT) | CSR_ENABLE, &flow->cpu1_csr);
> +	writel((4 << CSR_WAIT_WFI_SHIFT) | CSR_ENABLE, &flow->cpu2_csr);
> +	writel((8 << CSR_WAIT_WFI_SHIFT) | CSR_ENABLE, &flow->cpu3_csr);
> +
> +	writel(EVENT_MODE_STOP, &flow->halt_cpu1_events);
> +	writel(EVENT_MODE_STOP, &flow->halt_cpu2_events);
> +	writel(EVENT_MODE_STOP, &flow->halt_cpu3_events);
> +
> +	while (readl(&pmc->pmc_pwrgate_status) & ((1 << TEGRA_POWERGATE_CPU1) |
> +						  (1 << TEGRA_POWERGATE_CPU2) |
> +						  (1 << TEGRA_POWERGATE_CPU3)))
> +		/* wait */;
> +}

As discussed previously I don't quite understand why the sequence:

	1) program CSR registers
	2) program halt events
	3) power on CPUs

does not work. Testing shows that PSCI will work with that sequence once
the kernel is loaded. However I can also confirm that U-Boot doesn't see
the power partition status updated to "off", so I assume the partitions
will indeed still be powered on if we change the sequence.

So until we find out why that's happening I think it's safe to go with
the above sequence, since it does what we want. Perhaps add a comment
describing the ambiguity?

Also as a cosmetic cleanup, perhaps rather than checking the PMC power
gate status register you check bit 16 of each CPU's CSR register, which
should mirror the corresponding power gate status bit. That way you
don't need to access the PMC registers but restrict register accesses to
a single IP block in this code.

Thierry
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