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Date:	Mon, 05 Jan 2015 09:05:06 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Liviu Dudau <Liviu.Dudau@....com>,
	Russell King <linux@....linux.org.uk>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <Mark.Rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Haojian Zhuang <haojian.zhuang@...aro.org>
CC:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] irqchip: gic: Allow interrupt level to be set for
 PPIs.

Hi Liviu,

On 01/12/14 12:45, Liviu Dudau wrote:
> During a recent cleanup of the arm64 DTs it has become clear that
> the handling of PPIs in xxxx_set_type() is incorrect. The ARM TRMs
> for GICv2 and later allow for "implementation defined" support for
> setting the edge or level type of the PPI interrupts and don't restrict
> the activation level of the signal. Current ARM implementations
> do restrict the PPI level type to IRQ_TYPE_LEVEL_LOW, but licensees
> of the IP can decide to shoot themselves in the foot at any time.
> 
> Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> ---
> 
> Made a stupid mistake in v2 and got my bit test confused with logical test.
> 
>  Documentation/devicetree/bindings/arm/gic.txt |  8 ++++++--
>  drivers/irqchip/irq-gic-common.c              | 21 +++++++++++++--------
>  drivers/irqchip/irq-gic-common.h              |  2 +-
>  drivers/irqchip/irq-gic-v3.c                  |  8 ++++----
>  drivers/irqchip/irq-gic.c                     |  9 ++++++---
>  drivers/irqchip/irq-hip04.c                   |  9 ++++++---
>  6 files changed, 36 insertions(+), 21 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/arm/gic.txt b/Documentation/devicetree/bindings/arm/gic.txt
> index 8112d0c..c97484b 100644
> --- a/Documentation/devicetree/bindings/arm/gic.txt
> +++ b/Documentation/devicetree/bindings/arm/gic.txt
> @@ -32,12 +32,16 @@ Main node required properties:
>    The 3rd cell is the flags, encoded as follows:
>  	bits[3:0] trigger type and level flags.
>  		1 = low-to-high edge triggered
> -		2 = high-to-low edge triggered
> +		2 = high-to-low edge triggered (invalid for SPIs)
>  		4 = active high level-sensitive
> -		8 = active low level-sensitive
> +		8 = active low level-sensitive (invalid for SPIs).
>  	bits[15:8] PPI interrupt cpu mask.  Each bit corresponds to each of
>  	the 8 possible cpus attached to the GIC.  A bit set to '1' indicated
>  	the interrupt is wired to that CPU.  Only valid for PPI interrupts.
> +	Also note that the configurability of PPI interrupts is IMPLEMENTATION
> +	DEFINED and as such not guaranteed to be present (most SoC available
> +	in 2014 seem to ignore the setting of this flag and use the hardware
> +	default value).
>  
>  - reg : Specifies base physical address(s) and size of the GIC registers. The
>    first region is the GIC distributor register base and size. The 2nd region is
> diff --git a/drivers/irqchip/irq-gic-common.c b/drivers/irqchip/irq-gic-common.c
> index 61541ff..ffee521 100644
> --- a/drivers/irqchip/irq-gic-common.c
> +++ b/drivers/irqchip/irq-gic-common.c
> @@ -21,7 +21,7 @@
>  
>  #include "irq-gic-common.h"
>  
> -void gic_configure_irq(unsigned int irq, unsigned int type,
> +int gic_configure_irq(unsigned int irq, unsigned int type,
>  		       void __iomem *base, void (*sync_access)(void))
>  {
>  	u32 enablemask = 1 << (irq % 32);
> @@ -29,16 +29,17 @@ void gic_configure_irq(unsigned int irq, unsigned int type,
>  	u32 confmask = 0x2 << ((irq % 16) * 2);
>  	u32 confoff = (irq / 16) * 4;
>  	bool enabled = false;
> -	u32 val;
> +	u32 val, oldval;
> +	int ret = 0;
>  
>  	/*
>  	 * Read current configuration register, and insert the config
>  	 * for "irq", depending on "type".
>  	 */
> -	val = readl_relaxed(base + GIC_DIST_CONFIG + confoff);
> -	if (type == IRQ_TYPE_LEVEL_HIGH)
> +	val = oldval = readl_relaxed(base + GIC_DIST_CONFIG + confoff);
> +	if (type & IRQ_TYPE_LEVEL_MASK)
>  		val &= ~confmask;
> -	else if (type == IRQ_TYPE_EDGE_RISING)
> +	else if (type & IRQ_TYPE_EDGE_BOTH)
>  		val |= confmask;
>  
>  	/*
> @@ -54,15 +55,19 @@ void gic_configure_irq(unsigned int irq, unsigned int type,
>  
>  	/*
>  	 * Write back the new configuration, and possibly re-enable
> -	 * the interrupt.
> +	 * the interrupt. If we tried to write a new configuration and failed,
> +	 * return an error.
>  	 */
>  	writel_relaxed(val, base + GIC_DIST_CONFIG + confoff);
> -
> -	if (enabled)
> +	if (readl_relaxed(base + GIC_DIST_CONFIG + confoff) != val && val != oldval)
> +		ret = -EINVAL;
> +	else if (enabled)
>  		writel_relaxed(enablemask, base + GIC_DIST_ENABLE_SET + enableoff);

So if you change the configuration of an enabled interrupt and fail to
do so, you end-up with the interrupt disabled. This is a change in
behaviour, and is likely to introduce regressions.

>  
>  	if (sync_access)
>  		sync_access();
> +
> +	return ret;
>  }
>  
>  void __init gic_dist_config(void __iomem *base, int gic_irqs,
> diff --git a/drivers/irqchip/irq-gic-common.h b/drivers/irqchip/irq-gic-common.h
> index b41f024..35a9884 100644
> --- a/drivers/irqchip/irq-gic-common.h
> +++ b/drivers/irqchip/irq-gic-common.h
> @@ -20,7 +20,7 @@
>  #include <linux/of.h>
>  #include <linux/irqdomain.h>
>  
> -void gic_configure_irq(unsigned int irq, unsigned int type,
> +int gic_configure_irq(unsigned int irq, unsigned int type,
>                         void __iomem *base, void (*sync_access)(void));
>  void gic_dist_config(void __iomem *base, int gic_irqs,
>  		     void (*sync_access)(void));
> diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c
> index 1a146cc..6e50803 100644
> --- a/drivers/irqchip/irq-gic-v3.c
> +++ b/drivers/irqchip/irq-gic-v3.c
> @@ -238,7 +238,9 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
>  	if (irq < 16)
>  		return -EINVAL;
>  
> -	if (type != IRQ_TYPE_LEVEL_HIGH && type != IRQ_TYPE_EDGE_RISING)
> +	/* SPIs have restrictions on the supported types */
> +	if (irq >= 32 && type != IRQ_TYPE_LEVEL_HIGH &&
> +			 type != IRQ_TYPE_EDGE_RISING)
>  		return -EINVAL;
>  
>  	if (gic_irq_in_rdist(d)) {
> @@ -249,9 +251,7 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
>  		rwp_wait = gic_dist_wait_for_rwp;
>  	}
>  
> -	gic_configure_irq(irq, type, base, rwp_wait);
> -
> -	return 0;
> +	return gic_configure_irq(irq, type, base, rwp_wait);
>  }
>  
>  static u64 gic_mpidr_to_affinity(u64 mpidr)
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index d617ee5..4634cf7 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -188,12 +188,15 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
>  {
>  	void __iomem *base = gic_dist_base(d);
>  	unsigned int gicirq = gic_irq(d);
> +	int ret;
>  
>  	/* Interrupt configuration for SGIs can't be changed */
>  	if (gicirq < 16)
>  		return -EINVAL;
>  
> -	if (type != IRQ_TYPE_LEVEL_HIGH && type != IRQ_TYPE_EDGE_RISING)
> +	/* SPIs have restrictions on the supported types */
> +	if (gicirq >= 32 && type != IRQ_TYPE_LEVEL_HIGH &&
> +			    type != IRQ_TYPE_EDGE_RISING)
>  		return -EINVAL;
>  
>  	raw_spin_lock(&irq_controller_lock);
> @@ -201,11 +204,11 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
>  	if (gic_arch_extn.irq_set_type)
>  		gic_arch_extn.irq_set_type(d, type);
>  
> -	gic_configure_irq(gicirq, type, base, NULL);
> +	ret = gic_configure_irq(gicirq, type, base, NULL);
>  
>  	raw_spin_unlock(&irq_controller_lock);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static int gic_retrigger(struct irq_data *d)
> diff --git a/drivers/irqchip/irq-hip04.c b/drivers/irqchip/irq-hip04.c
> index 29b8f21..d059e66 100644
> --- a/drivers/irqchip/irq-hip04.c
> +++ b/drivers/irqchip/irq-hip04.c
> @@ -120,21 +120,24 @@ static int hip04_irq_set_type(struct irq_data *d, unsigned int type)
>  {
>  	void __iomem *base = hip04_dist_base(d);
>  	unsigned int irq = hip04_irq(d);
> +	int ret;
>  
>  	/* Interrupt configuration for SGIs can't be changed */
>  	if (irq < 16)
>  		return -EINVAL;
>  
> -	if (type != IRQ_TYPE_LEVEL_HIGH && type != IRQ_TYPE_EDGE_RISING)
> +	/* SPIs have restrictions on the supported types */
> +	if (irq >= 32 && type != IRQ_TYPE_LEVEL_HIGH &&
> +			 type != IRQ_TYPE_EDGE_RISING)
>  		return -EINVAL;
>  
>  	raw_spin_lock(&irq_controller_lock);
>  
> -	gic_configure_irq(irq, type, base, NULL);
> +	ret = gic_configure_irq(irq, type, base, NULL);
>  
>  	raw_spin_unlock(&irq_controller_lock);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  #ifdef CONFIG_SMP
> 

I have exactly zero knowledge about the hip04 controller, and despite it
looking like a GIC, it is quite different from the real thing. I'd like
to see confirmation from the HiSilicon guys that this is the right thing
to do, and possibly this to be moved to a separate patch if that
requires extra changes.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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