linux-kernel - Re: [PATCH 1/2] irqchip/gic: Handle non-standard SGI deactivation on Samsung's Franken-GIC

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Message-ID: <d1301d9c-5529-0089-f163-2a728055712c@samsung.com>
Date:   Tue, 15 Sep 2020 16:06:27 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] irqchip/gic: Handle non-standard SGI deactivation
 on Samsung's Franken-GIC

On 15.09.2020 15:39, Marc Zyngier wrote:
> The GIC available on some of Samsung's A9-based platform is
> thankfully one of a kind. On top of not presenting a banked
> programing model (each CPU has its own base addresses for both
> distributor and CPU interface), it also encodes the source CPU
> for SGIs in the INTID read from IAR, and requires this exact
> value to be written back to EOI.
>
> Without this, interrupts are never deactivated, and the kernel
> grinds to a halt.
>
> Work around it by stashing the INTID for in-flight SGIs, and
> using that value on EOI. This only works because we don't nest
> SGIs.
>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Fixes: ac063232d4b0 ("irqchip/gic: Configure SGIs as standard interrupts")
> Signed-off-by: Marc Zyngier <maz@...nel.org>

Works fine, thanks!

Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>

> ---
>   drivers/irqchip/irq-gic.c | 49 +++++++++++++++++++++++++++++++++++++--
>   1 file changed, 47 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index 4be2b62f816f..84a2d2a1aab7 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -150,10 +150,37 @@ static inline void gic_set_base_accessor(struct gic_chip_data *data,
>   {
>   	data->get_base = f;
>   }
> +
> +static DEFINE_STATIC_KEY_FALSE(frankengic_key);
> +static DEFINE_PER_CPU(u32, sgi_intid);
> +
> +static void enable_frankengic(void)
> +{
> +	static_branch_enable(&frankengic_key);
> +}
> +
> +static inline bool is_frankengic(void)
> +{
> +	return static_branch_unlikely(&frankengic_key);
> +}
> +
> +static inline void set_sgi_intid(u32 intid)
> +{
> +	this_cpu_write(sgi_intid, intid);
> +}
> +
> +static inline u32 get_sgi_intid(void)
> +{
> +	return this_cpu_read(sgi_intid);
> +}
>   #else
>   #define gic_data_dist_base(d)	((d)->dist_base.common_base)
>   #define gic_data_cpu_base(d)	((d)->cpu_base.common_base)
>   #define gic_set_base_accessor(d, f)
> +#define enable_frankengic()	do { } while(0)
> +#define is_frankengic()		false
> +#define set_sgi_intid(i)	do { } while(0)
> +#define get_sgi_intid()		0
>   #endif
>   
>   static inline void __iomem *gic_dist_base(struct irq_data *d)
> @@ -226,7 +253,12 @@ static void gic_unmask_irq(struct irq_data *d)
>   
>   static void gic_eoi_irq(struct irq_data *d)
>   {
> -	writel_relaxed(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI);
> +	u32 hwirq = gic_irq(d);
> +
> +	if (is_frankengic() && hwirq < 16)
> +		hwirq = get_sgi_intid();
> +
> +	writel_relaxed(hwirq, gic_cpu_base(d) + GIC_CPU_EOI);
>   }
>   
>   static void gic_eoimode1_eoi_irq(struct irq_data *d)
> @@ -348,8 +380,20 @@ static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs)
>   		 *
>   		 * Pairs with the write barrier in gic_ipi_send_mask
>   		 */
> -		if (irqnr <= 15)
> +		if (irqnr <= 15) {
>   			smp_rmb();
> +
> +			/*
> +			 * Samsung's funky GIC encodes the source CPU in
> +			 * GICC_IAR, leading to the deactivation to fail if
> +			 * not written back as is to GICC_EOI.  Stash the
> +			 * INTID away for gic_eoi_irq() to write back.
> +			 * This only works because we don't nest SGIs...
> +			 */
> +			if (is_frankengic())
> +				set_sgi_intid(irqstat);
> +		}
> +
>   		handle_domain_irq(gic->domain, irqnr, regs);
>   	} while (1);
>   }
> @@ -1142,6 +1186,7 @@ static int gic_init_bases(struct gic_chip_data *gic,
>   				gic->raw_cpu_base + offset;
>   		}
>   
> +		enable_frankengic();
>   		gic_set_base_accessor(gic, gic_get_percpu_base);
>   	} else {
>   		/* Normal, sane GIC... */

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland