linux-kernel - Re: [PATCH] irqchip/gic-v3-its: Mark GIC as non-shareable by OF property

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Message-ID: <86sf7ue6yk.wl-maz@kernel.org>
Date:   Mon, 04 Sep 2023 08:24:51 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Fang Xiang <fangxiang3@...omi.com>
Cc:     <tglx@...utronix.de>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] irqchip/gic-v3-its: Mark GIC as non-shareable by OF property

On Mon, 04 Sep 2023 03:04:31 +0100,
Fang Xiang <fangxiang3@...omi.com> wrote:
> 
> GIC600/GIC700 integration in some platforms does not support the
> sharability feature. Commit a8707f553884 ("irqchip/gic-v3: Add
> Rockchip 3588001 erratum workaround") added flags to indicate the
> integration design error, but the quirk is just applied with
> RK3588/RK3588S and GIC600.
> 
> The property are named "force-non-shareable" to be vendor agnostic,
> since apparently similar integration design errors exist in other
> platforms and they can reuse the same property in their GIC ITS
> device-node.

No. If this is a problem, this must be dealt with in the following
manner:

- a standard property, which is documented in the ITS binding
- an equivalent ACPI property, equally documented
- separate instances of the property for the core GIC and the ITS
  (because the RDs are *not* defined at the ITS level)

> 
> Signed-off-by: Fang Xiang <fangxiang3@...omi.com>
> ---
>  drivers/irqchip/irq-gic-v3-its.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
> index e0c2b10d154d..2e92eac1e5f3 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -5055,6 +5055,16 @@ static int __init its_compute_its_list_map(struct resource *res,
>         return its_number;
>  }
> 
> +static void its_of_update_shareability(struct its_node *its)
> +{
> +       if (!fwnode_property_present(its->fwnode_handle,
> +                               "force-non-shareable"))
> +               return;
> +
> +       its->flags |= ITS_FLAGS_FORCE_NON_SHAREABLE;
> +       gic_rdists->flags |= RDIST_FLAGS_FORCE_NON_SHAREABLE;

There is no reason why we should conflate the two, other than your
implementation being monolithic.

> +}
> +
>  static int __init its_probe_one(struct resource *res,
>                                 struct fwnode_handle *handle, int numa_node)
>  {
> @@ -5130,6 +5140,7 @@ static int __init its_probe_one(struct resource *res,
>         its->msi_domain_flags = IRQ_DOMAIN_FLAG_ISOLATED_MSI;
> 
>         its_enable_quirks(its);
> +       its_of_update_shareability(its);

As mentioned above, we need a mechanism that works across firmware implementations.

> 
>         err = its_alloc_tables(its);
>         if (err)
> --
> 2.34.1
> 
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Please fix your email setup.

	M.

-- 
Without deviation from the norm, progress is not possible.