Re: [PATCH 1/3] irqchip/GIC: Add workaround for aliased GIC400

[Duc Dang]

On Sun, Sep 13, 2015 at 4:14 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
>
> The GICv2 architecture mandates that the two 4kB GIC regions are
> contiguous, and on two separate physical pages (so that access to
> the second page can be trapped by a hypervisor). This doesn't work
> very well when PAGE_SIZE is 64kB.
>
> A relatively common hack^Wway to work around this is to alias each
> 4kB region over its own 64kB page. Of course in this case, the base
> address you want to use is not really the begining of the region,
> but base + 60kB (so that you get a contiguous 8kB region over two
> distinct pages).
>
> Normally, this would be described in DT with a new property, but
> some HW is already out there, and the firmware makes sure that
> it will override whatever you put in the GIC node. Duh. And of course,
> said firmware source code is not available, despite being based
> on u-boot.
>
> The workaround is to detect the case where the CPU interface size
> is set to 128kB, and verify the aliasing by checking that the ID
> register for GIC400 (which is the only GIC wired this way so far)
> is the same at base and base + 0xF000. In this case, we update
> the GIC base address and let it roll.

Hi Marc,

When booting ACPI with X-Gene Mustang, I saw it hangs when EOI mode is
enabled, should we have ACPI version for gic_check_eoimode as well?

Regards,
Duc Dang.
>
> And if you feel slightly sick by looking at this, rest assured that
> I do too...
>
> Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
>  drivers/irqchip/irq-gic.c | 44 +++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 39 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
> index e6b7ed5..a947057 100644
> --- a/drivers/irqchip/irq-gic.c
> +++ b/drivers/irqchip/irq-gic.c
> @@ -1119,12 +1119,49 @@ void __init gic_init_bases(unsigned int gic_nr, int irq_start,
>  #ifdef CONFIG_OF
>  static int gic_cnt __initdata;
>
> +static bool gic_check_eoimode(struct device_node *node, void __iomem **base)
> +{
> +       struct resource cpuif_res;
> +
> +       of_address_to_resource(node, 1, &cpuif_res);
> +
> +       if (!is_hyp_mode_available())
> +               return false;
> +       if (resource_size(&cpuif_res) < SZ_8K)
> +               return false;
> +       if (resource_size(&cpuif_res) == SZ_128K) {
> +               u32 val_low, val_high;
> +
> +               /*
> +                * Verify that we have the first 4kB of a GIC400
> +                * aliased over the first 64kB by checking the
> +                * GICC_IIDR register on both ends.
> +                */
> +               val_low = readl_relaxed(*base + GIC_CPU_IDENT);
> +               val_high = readl_relaxed(*base + GIC_CPU_IDENT + 0xf000);
> +               if ((val_low & 0xffff0fff) != 0x0202043B ||
> +                   val_low != val_high)
> +                       return false;
> +
> +               /*
> +                * Move the base up by 60kB, so that we have a 8kB
> +                * contiguous region, which allows us to use GICC_DIR
> +                * at its normal offset. Please pass me that bucket.
> +                */
> +               *base += 0xf000;
> +               cpuif_res.start += 0xf000;
> +               pr_warn("GIC: Adjusting CPU interface base to %pa",
> +                       &cpuif_res.start);
> +       }
> +
> +       return true;
> +}
> +
>  static int __init
>  gic_of_init(struct device_node *node, struct device_node *parent)
>  {
>         void __iomem *cpu_base;
>         void __iomem *dist_base;
> -       struct resource cpu_res;
>         u32 percpu_offset;
>         int irq;
>
> @@ -1137,14 +1174,11 @@ gic_of_init(struct device_node *node, struct device_node *parent)
>         cpu_base = of_iomap(node, 1);
>         WARN(!cpu_base, "unable to map gic cpu registers\n");
>
> -       of_address_to_resource(node, 1, &cpu_res);
> -
>         /*
>          * Disable split EOI/Deactivate if either HYP is not available
>          * or the CPU interface is too small.
>          */
> -       if (gic_cnt == 0 && (!is_hyp_mode_available() ||
> -                            resource_size(&cpu_res) < SZ_8K))
> +       if (gic_cnt == 0 && !gic_check_eoimode(node, &cpu_base))
>                 static_key_slow_dec(&supports_deactivate);
>
>         if (of_property_read_u32(node, "cpu-offset", &percpu_offset))
> --
> 2.1.4
>
>
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