linux-kernel - Re: [PATCH v3 13/17] ARM64 / ACPI: Add GICv2 specific ACPI boot support

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Date:	Thu, 04 Sep 2014 12:39:45 +0200
From:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>, linux-arm-kernel@...ts.infradead.org
CC:	Mark Rutland <mark.rutland@....com>, linaro-acpi@...ts.linaro.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Lv Zheng <lv.zheng@...el.com>, Rob Herring <robh@...nel.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Robert Moore <robert.moore@...el.com>,
	linux-acpi@...r.kernel.org, Grant Likely <grant.likely@...aro.org>,
	Charles.Garcia-Tobin@....com, Robert Richter <rric@...nel.org>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Mark Brown <broonie@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Graeme Gregory <graeme.gregory@...aro.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org, Hanjun Guo <hanjun.guo@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v3 13/17] ARM64 / ACPI: Add GICv2 specific ACPI boot support

On 04.09.2014 12:14, Arnd Bergmann wrote:
> On Thursday 04 September 2014 12:10:28 Tomasz Nowicki wrote:
>> On 03.09.2014 20:42, Arnd Bergmann wrote:
>>> On Monday 01 September 2014 22:57:51 Hanjun Guo wrote:
>>>> +       /* Collect CPU base addresses */
>>>> +       count = acpi_parse_entries(sizeof(struct acpi_table_madt),
>>>> +                                  gic_acpi_parse_madt_cpu, table,
>>>> +                                  ACPI_MADT_TYPE_GENERIC_INTERRUPT,
>>>> +                                  ACPI_MAX_GIC_CPU_INTERFACE_ENTRIES);
>>>> +       if (count < 0) {
>>>> +               pr_err("Error during GICC entries parsing\n");
>>>> +               return -EFAULT;
>>>> +       } else if (!count) {
>>>> +               /* No GICC entries provided, use address from MADT header */
>>>> +               struct acpi_table_madt *madt = (struct acpi_table_madt *)table;
>>>> +
>>>> +               if (!madt->address)
>>>> +                       return -EFAULT;
>>>> +
>>>> +               cpu_phy_base = (u64)madt->address;
>>>> +       }
>>>
>>> After I read through ACPI-5.1 section 5.2.12.14, I wonder if this is the
>>> best way to treat a missing ACPI_MADT_TYPE_GENERIC_INTERRUPT table.
>>>
>>> Do we expect to see those in practice? It seems like using the x86 local
>>> APIC address as a fallback for the GIC address is not something we
>>> should do unless we absolutely have to support a system that doesn't
>>> have the GIC table.
>>
>> No, we do not expect and hopefully there will be no such
>>
>> But, we are trying to be as much as possible inline with 5.1 spec,
>> 5.2.12.14 says:
>> [...]
>> If provided here (CPU physical base address), the "Local Interrupt
>> Controller Address" field in the MADT must be ignored by the OSPM.
>> [...]
>>
>
> Yes, that's what I saw. So ignoring it all the time is fine, right?
> Presumably the madt->address field is only referenced here because
> some pre-5.1 implementations used to do that.

So this is very vague statement. On the one hand it would make sense to 
take madt->address if we have no GICC entries. On the other hand we do 
not support non-banked GIC cpu registers. So all of then need to have 
the same cpu_base_address. What if one has null address? Should the rest 
take madt->address? I think you are right, I will remove madt->address 
fallback and simplify the code.

Thanks,
Tomasz
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