Message-ID: <CAK9=C2XrExRLihwveMxs-Ourr+8bXja5UAmN_muAJz5FSpFW8A@mail.gmail.com>
Date: Wed, 14 Jan 2026 14:27:18 +0530
From: Anup Patel <apatel@...tanamicro.com>
To: Yicong Yang <yang.yicong@...oheart.com>
Cc: anup@...infault.org, tglx@...nel.org, pjw@...nel.org, palmer@...belt.com, 
	aou@...s.berkeley.edu, alex@...ti.fr, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, geshijian@...oheart.com, 
	weidong.wd@...oheart.com
Subject: Re: [PATCH] irqchip/riscv-aplic: Register the driver prior to device creation

On Wed, Jan 14, 2026 at 12:08 PM Yicong Yang <yang.yicong@...oheart.com> wrote:
>
> On RISC-V the APLIC serves part of the GSI interrupts, but unlike
> other arthitecture it's initialized a bit late on ACPI based
> system:
> - the spec only mandates the report in DSDT (riscv-brs rule AML_100)
>   so the APLIC is created as platform_device when scanning DSDT
> - the driver is registered and initialize the device in device_initcall
>   stage
>
> The creation of devices depends on APLIC is deferred after the APLIC
> is initialized (when the driver calls acpi_dev_clear_dependencies),
> not like most other devices which is created when scanning the DSDT.
> The affected devices include those declare the dependency explicitly
> by ACPI _DEP method and _PRT for PCIe host bridge and those require
> their interrupts as GSI. Furhtermore, the deferred creation is
> performed in an async way (queued in the system_dfl_wq workqueue)
> but all contend on the acpi_scan_lock.
>
> Since the deferred devcie creation is asynchronous and will contend
> for the same lock, the order and timing is not certain. And the time
> is late enough for the device creation running parallel with the init
> task. This will lead to below issues (also observed on our platforms):
> - the console/tty device is created lately and sometimes it's not ready
>   when init task check for its presence. the system will crash in the
>   latter case since the init task always requires a valid console.
> - the root device will by probed and registered lately (e.g. NVME,
>   after the init task executed) and may run into the rescue shell if
>   root device is not found.
>
> We'll run into the issues more often in linuxboot since the init tasks
> is more simpler (usually u-root) and will check for the console/root
> devices more earlier.
>
> Solve this by promote the APLIC driver register stage to core_initcall
> which is prior to the APLIC device creation. So the dependency for
> the GSI is met earlier. The key system devices like tty/PCI will be
> created earlier when scanning ACPI namespace in a synchronous manner
> and won't be parallel with the init task. So it's certain to have
> a console/root device when the init task running.

Changing the driver registration priority is not going to help. For DT,
we should rely on fw_devlink to ensure APLIC is probed before
drivers consuming APLIC interrupts. For ACPI in the RISC-V world,
the APLIC probe ordering using GSI mappings and _DEP objects.

There was a recent discussion on this so refer:
https://www.spinics.net/lists/kernel/msg5938816.html

Regards,
Anup

>
> Signed-off-by: Yicong Yang <yang.yicong@...oheart.com>
> ---
>  drivers/irqchip/irq-riscv-aplic-main.c | 14 +++++++++++++-
>  1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/irqchip/irq-riscv-aplic-main.c b/drivers/irqchip/irq-riscv-aplic-main.c
> index 93e7c51f944a..86a3d19b6b24 100644
> --- a/drivers/irqchip/irq-riscv-aplic-main.c
> +++ b/drivers/irqchip/irq-riscv-aplic-main.c
> @@ -231,4 +231,16 @@ static struct platform_driver aplic_driver = {
>         },
>         .probe = aplic_probe,
>  };
> -builtin_platform_driver(aplic_driver);
> +
> +static int __init aplic_driver_init(void)
> +{
> +       return platform_driver_register(&aplic_driver);
> +}
> +
> +/*
> + * APLIC serves part of GSI interrupts and some key system devices like
> + * TTY/PCI depends on its initialization. Register the driver prior to
> + * APLIC device (on ACPI it's created in subsys_initcall when scanning
> + * the namespace devices) to make the GSI service ready early.
> + */
> +core_initcall(aplic_driver_init);
> --
> 2.34.1
>
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