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SubjectRe: [PATCH 1/2] irqchip/gic: Handle non-standard SGI deactivation on Samsung's Franken-GIC
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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@samsung.com>
> Fixes: ac063232d4b0 ("irqchip/gic: Configure SGIs as standard interrupts")
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Works fine, thanks!

Tested-by: Marek Szyprowski <m.szyprowski@samsung.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

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