linux-kernel - Re: [PATCH v4 14/18] ARM64 / ACPI: Add GICv2 specific ACPI boot support

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Message-ID: <20140917151445.GF10392@e104818-lin.cambridge.arm.com>
Date:	Wed, 17 Sep 2014 16:14:45 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
Cc:	"jcm@...hat.com" <jcm@...hat.com>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Mark Rutland <Mark.Rutland@....com>,
	Olof Johansson <olof@...om.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Lv Zheng <lv.zheng@...el.com>,
	Robert Moore <robert.moore@...el.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 14/18] ARM64 / ACPI: Add GICv2 specific ACPI boot
 support

On Wed, Sep 17, 2014 at 08:40:08AM +0100, Tomasz Nowicki wrote:
> On 15.09.2014 18:42, Catalin Marinas wrote:
> > On Mon, Sep 15, 2014 at 05:16:21PM +0100, Jon Masters wrote:
> >> On 09/15/2014 11:01 AM, Catalin Marinas wrote:
> >>> On Fri, Sep 12, 2014 at 03:00:12PM +0100, Hanjun Guo wrote:
> >>>> diff --git a/arch/arm64/kernel/acpi.c b/arch/arm64/kernel/acpi.c
> >>>> index 5b3546b..9869377 100644
> >>>> --- a/arch/arm64/kernel/acpi.c
> >>>> +++ b/arch/arm64/kernel/acpi.c
> >>>> @@ -23,6 +23,7 @@
> >>>>   #include <linux/irqdomain.h>
> >>>>   #include <linux/bootmem.h>
> >>>>   #include <linux/smp.h>
> >>>> +#include <linux/irqchip/arm-gic-acpi.h>
> >>>>
> >>>>   #include <asm/cputype.h>
> >>>>   #include <asm/cpu_ops.h>
> >>>> @@ -312,6 +313,28 @@ void __init acpi_boot_table_init(void)
> >>>>   		pr_err("Can't find FADT or error happened during parsing FADT\n");
> >>>>   }
> >>>>
> >>>> +void __init acpi_gic_init(void)
> >>>> +{
> >>>> +	struct acpi_table_header *table;
> >>>> +	acpi_status status;
> >>>> +	acpi_size tbl_size;
> >>>> +	int err;
> >>>> +
> >>>> +	status = acpi_get_table_with_size(ACPI_SIG_MADT, 0, &table, &tbl_size);
> >>>> +	if (ACPI_FAILURE(status)) {
> >>>> +		const char *msg = acpi_format_exception(status);
> >>>> +
> >>>> +		pr_err("Failed to get MADT table, %s\n", msg);
> >>>> +		return;
> >>>> +	}
> >>>> +
> >>>> +	err = gic_v2_acpi_init(table);
> >>>> +	if (err)
> >>>> +		pr_err("Failed to initialize GIC IRQ controller");
> >>>> +
> >>>> +	early_acpi_os_unmap_memory((char *)table, tbl_size);
> >>>> +}
> >>>
> >>> Maybe this was discussed already but why does this function need to live
> >>> under arch/arm64? Isn't the driver code more appropriate?
> 
> There will be another call here for GICv3 so this function will merge 
> common logic for them. As Jon pointed out, we are planning to add ACPI 
> flag which indicates GICv3 or GICv2(m) IRQ controller in advance.

We have GIC stuff for ACPI scattered around the kernel
(arch/arm64/kernel/acpi.c, drivers/acpi/processor_core.c,
drivers/irqchip/). It would be nicer if we find some common place for
them, even if that is something under drivers/acpi/ or drivers/irqchip/
(we even have an irq-gic-common.c).

> >> Well there's two halves to this, right? There's the MADT parsing/setup,
> >> which is architecture specific, and then there's the GIC irqchip
> >> initialization which lives under drivers.
> >
> > I think it gets worse, this function is called from irqchip_init(). I
> > would have been slightly happier if it was called from the arm64
> > init_IRQ(). But putting an ARM specific GIC initialisation call in a
> > generic irqchip_init() just looks weird. Can we do anything better here?
> 
> Yes this was discussed, please have a look at: 
> https://lkml.org/lkml/2014/9/1/555
> We had this in init_IRQ() in previous patch set, then we got feedback 
> irqchip_init() is more appropriate. We can move it back to init_IRQ() 
> and I am sold on this.

The irqchip_init() is indeed the place to call other interrupt
controller initialisation functions but what I don't particularly like
is calling the GIC one directly while the OF ones are checked against a
match string. For GICv3 and later, do you plan to use the same
acpi_gic_init() functions? Otherwise we could do something like
ACPI_IRQCHIP_DECLARE() similar to the OF ones and a common function that
probes whatever is built into the kernel.

-- 
Catalin
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