Subject: [PATCH v3 10/15] ARM: vexpress/dcscb: add CPU use counts to the power up/down API implementation

From: [email-masked] (Santosh Shilimkar)
Date: Fri, 1 Feb 2013 11:23:17 +0530

On Tuesday 29 January 2013 01:21 PM, Nicolas Pitre wrote:
> It is possible for a CPU to be told to power up before it managed
> to power itself down.  Solve this race with a usage count as mandated
> by the API definition.
>
> Signed-off-by: nicolas Pitre <[email-masked]>
> ---
>   arch/arm/mach-vexpress/dcscb.c | 77 +++++++++++++++++++++++++++++++++---------
>   1 file changed, 61 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm/mach-vexpress/dcscb.c b/arch/arm/mach-vexpress/dcscb.c
> index 677ced9efc..f993608944 100644
> --- a/arch/arm/mach-vexpress/dcscb.c
> +++ b/arch/arm/mach-vexpress/dcscb.c
> @@ -45,6 +45,7 @@
>   static arch_spinlock_t dcscb_lock = __ARCH_SPIN_LOCK_UNLOCKED;
>
>   static void __iomem *dcscb_base;
> +static int dcscb_use_count[4][2];
>
>   static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
>   {
> @@ -61,14 +62,27 @@ static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
>   	local_irq_disable();
>   	arch_spin_lock(&dcscb_lock);
>
> -	rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
> -	if (rst_hold & (1 << 8)) {
> -		/* remove cluster reset and add individual CPU's reset */
> -		rst_hold &= ~(1 << 8);
> -		rst_hold |= 0xf;
> +	dcscb_use_count[cpu][cluster]++;
> +	if (dcscb_use_count[cpu][cluster] == 1) {
> +		rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
> +		if (rst_hold & (1 << 8)) {
> +			/* remove cluster reset and add individual CPU's reset */
> +			rst_hold &= ~(1 << 8);
> +			rst_hold |= 0xf;
> +		}
> +		rst_hold &= ~(cpumask | (cpumask << 4));
> +		writel(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
> +	} else if (dcscb_use_count[cpu][cluster] != 2) {
> +		/*
> +		 * The only possible values are:
> +		 * 0 = CPU down
> +		 * 1 = CPU (still) up
> +		 * 2 = CPU requested to be up before it had a chance
> +		 *     to actually make itself down.
> +		 * Any other value is a bug.
> +		 */
> +		BUG();
No strong opinion but would switch case be better here ?

>   	}
> -	rst_hold &= ~(cpumask | (cpumask << 4));
> -	writel(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
>
>   	arch_spin_unlock(&dcscb_lock);
>   	local_irq_enable();
> @@ -78,7 +92,8 @@ static int dcscb_power_up(unsigned int cpu, unsigned int cluster)
>
>   static void dcscb_power_down(void)
>   {
> -	unsigned int mpidr, cpu, cluster, rst_hold, cpumask, last_man;
> +	unsigned int mpidr, cpu, cluster, rst_hold, cpumask;
> +	bool last_man = false, skip_wfi = false;
>
>   	mpidr = read_cpuid_mpidr();
>   	cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);
> @@ -89,13 +104,26 @@ static void dcscb_power_down(void)
>   	BUG_ON(cpu >= 4 || cluster >= 2);
>
>   	arch_spin_lock(&dcscb_lock);
> -	rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
> -	rst_hold |= cpumask;
> -	if (((rst_hold | (rst_hold >> 4)) & 0xf) == 0xf)
> -		rst_hold |= (1 << 8);
> -	writel(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
> +	dcscb_use_count[cpu][cluster]--;
> +	if (dcscb_use_count[cpu][cluster] == 0) {
> +		rst_hold = readl_relaxed(dcscb_base + RST_HOLD0 + cluster * 4);
> +		rst_hold |= cpumask;
> +		if (((rst_hold | (rst_hold >> 4)) & 0xf) == 0xf) {
> +			rst_hold |= (1 << 8);
> +			last_man = true;
> +		}
> +		writel(rst_hold, dcscb_base + RST_HOLD0 + cluster * 4);
> +	} else if (dcscb_use_count[cpu][cluster] == 1) {
> +		/*
> +		 * A power_up request went ahead of us.
> +		 * Even if we do not want to shut this CPU down,
> +		 * the caller expects a certain state as if the WFI
> +		 * was aborted.  So let's continue with cache cleaning.
> +		 */
> +		skip_wfi = true;
> +	} else
> +		BUG();
Same comment as above.

Rest looks fine.
Reviewed-by: Santosh Shilimkar <[email-masked]>