linux-kernel - Re: [PATCH V8 02/10] irqchip/loongson-pch-pic: Add ACPI init support

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Date:   Fri, 17 Dec 2021 12:45:24 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V8 02/10] irqchip/loongson-pch-pic: Add ACPI init support

Hi, Marc,

On Thu, Dec 16, 2021 at 11:06 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Thu, 16 Dec 2021 12:53:48 +0000,
> Huacai Chen <chenhuacai@...ngson.cn> wrote:
> >
> > We are preparing to add new Loongson (based on LoongArch, not compatible
> > with old MIPS-based Loongson) support. LoongArch use ACPI other than DT
> > as its boot protocol, so add ACPI init support.
> >
> > PCH-PIC/PCH-MSI stands for "Interrupt Controller" that described in
> > Section 5 of "Loongson 7A1000 Bridge User Manual". For more information
> > please refer Documentation/loongarch/irq-chip-model.rst.
> >
> > Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> > ---
> >  drivers/irqchip/irq-loongson-pch-pic.c | 108 ++++++++++++++++++-------
> >  1 file changed, 81 insertions(+), 27 deletions(-)
>
> [...]
>
> >
> > +#ifdef CONFIG_ACPI
> > +
> > +struct irq_domain *pch_pic_acpi_init(struct irq_domain *parent,
> > +                                     struct acpi_madt_bio_pic *acpi_pchpic)
>
> Who is calling this? This works the opposite way from what the arm64
> irqchips are doing. Why? I have the ugly feeling that this is called
> from the arch code, bypassing the existing infrastructure...
Yes, this is called from the arch code and a bit ugly, but I can't
find a better way to do this.

Is the "existing infrastructure" declare the irqchip init function
with  IRQCHIP_ACPI_DECLARE and the arch code only need to call
irqchip_init()? Then we have a problem: our irqchips have a 4 level
hierachy and the parent should be initialized before its children. In
FDT world this is not a problem, because of_irq_init() will sort
irqchip drivers to ensure the right order. But in ACPI world,
acpi_probe_device_table just call init functions in the linking order.
If we want to control the order, it seems we can only sort the drivers
in drivers/irq/Makefile. But I don't think this is a good idea...

If there are better solutions, please let me know. Thanks.

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