linux-kernel - Re: [PATCH v3 3/5] irqchip/gic-v3-its: Split allocation from initialisation of its

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Date:   Tue, 24 Oct 2023 10:48:31 +0200
From:   Dominic Rath <dominic.rath@...-augsburg.net>
To:     Lorenzo Pieralisi <lpieralisi@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-acpi@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Robin Murphy <robin.murphy@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Fang Xiang <fangxiang3@...omi.com>, bahle@...-augsburg.de,
        rath@...-augsburg.de
Subject: Re: [PATCH v3 3/5] irqchip/gic-v3-its: Split allocation from
 initialisation of its_node

Hi,

On Fri, Oct 06, 2023 at 02:59:27PM +0200, Lorenzo Pieralisi wrote:
> From: Marc Zyngier <maz@...nel.org>
> 
> In order to pave the way for more fancy quirk handling without making
> more of a mess of this terrible driver, split the allocation of the
> ITS descriptor (its_node) from the actual probing.

it seems that this change breaks MSI-X (MSI?) reception on at least
the TI AM64x, probably most/all of TI's recent devices (K3).

These devices rely on a quirk CONFIG_SOCIONEXT_SYNQUACER_PREITS that
uses an address from the dts specified e.g. as

  socionext,synquacer-pre-its = <0x1000000 0x400000>;

to configure a MSI base address that differs from the ARM default.

With this change, the quirk still sets its->get_msi_base and clears
IRQ_DOMAIN_FLAG_ISOLATED_MSI from its->msi_domain_flags during
its_of_probe, but both get overwritten again during its_probe_one
with the defaults.

Previously the defaults would be set first and then the quirks were
applied.

I have no idea whether TI's use of this quirk was "correct", but it did
work, and since 6.6-rc6 MSI-X has been broken for us.

Best Regards,
Dominic