linux-kernel - Re: [PATCH V3 10/10] acpi, gicv3, its: Use MADT ITS subtable to do PCI/MSI domain initialization.

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Date:	Fri, 12 Feb 2016 13:26:55 +0100
From:	Tomasz Nowicki <tn@...ihalf.com>
To:	Marc Zyngier <marc.zyngier@....com>, tglx@...utronix.de,
	jason@...edaemon.net, rjw@...ysocki.net, lorenzo.pieralisi@....com,
	robert.richter@...iumnetworks.com, shijie.huang@....com,
	guohanjun@...wei.com, Suravee.Suthikulpanit@....com,
	Charles Garcia-Tobin <charles.garcia-tobin@....com>
Cc:	mw@...ihalf.com, graeme.gregory@...aro.org,
	Catalin.Marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	hanjun.guo@...aro.org, linux-arm-kernel@...ts.infradead.org,
	ddaney.cavm@...il.com
Subject: Re: [PATCH V3 10/10] acpi, gicv3, its: Use MADT ITS subtable to do
 PCI/MSI domain initialization.

+ Charles

On 10.02.2016 13:02, Marc Zyngier wrote:
> On 19/01/16 13:11, Tomasz Nowicki wrote:
>> After refactoring DT code, we let ACPI to build ITS PCI MSI domain
>> and do requester ID to device ID translation using IORT table.
>>
>> We have now full PCI MSI domain stack, thus we can enable ITS initialization
>> from GICv3 core driver for ACPI scenario.
>>
>> Signed-off-by: Tomasz Nowicki <tn@...ihalf.com>
>> ---
>>   drivers/irqchip/irq-gic-v3-its-pci-msi.c | 44 +++++++++++++++++++++++++++++++-
>>   drivers/irqchip/irq-gic-v3.c             |  3 +--
>>   drivers/pci/msi.c                        |  3 +++
>>   3 files changed, 47 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its-pci-msi.c b/drivers/irqchip/irq-gic-v3-its-pci-msi.c
>> index 06165cb..7f0a958 100644
>> --- a/drivers/irqchip/irq-gic-v3-its-pci-msi.c
>> +++ b/drivers/irqchip/irq-gic-v3-its-pci-msi.c
>> @@ -15,6 +15,8 @@
>>    * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>    */
>>
>> +#include <linux/acpi.h>
>> +#include <linux/iort.h>
>>   #include <linux/msi.h>
>>   #include <linux/of.h>
>>   #include <linux/of_irq.h>
>> @@ -143,10 +145,50 @@ static int __init its_pci_of_msi_init(void)
>>   	return 0;
>>   }
>>
>> +#ifdef CONFIG_ACPI
>> +
>> +static int __init
>> +its_pci_msi_parse_madt(struct acpi_subtable_header *header,
>> +		    const unsigned long end)
>> +{
>> +	struct acpi_madt_generic_translator *its_entry;
>> +	struct fwnode_handle *domain_handle;
>> +
>> +	its_entry = (struct acpi_madt_generic_translator *)header;
>> +	domain_handle = iort_find_its_domain_token(its_entry->translation_id);
>> +	if (!domain_handle) {
>> +		pr_err("ITS@...lx: Unable to locate ITS domain handle\n",
>> +		       (long)its_entry->base_address);
>> +		return 0;
>> +	}
>> +
>> +	if (its_pci_msi_init_one(domain_handle))
>> +		return 0;
>> +
>> +	pci_msi_register_fwnode_provider(&iort_find_pci_domain_token);
>
> I'm a bit worried by this. You are registering this for each and every
> ITS that gets probed (useless, but why not). But also, you're using a
> hook that is designed to work at the bus level, without caring for the
> actual PCI devices. That's fine for something like GICv2m, which exposes
> a single domain, but I can't picture how this works when you have
> devices sitting behind a single RC that talk to different ITSs.
>
> My understanding is that IORT was behaving in a similar way the msi-map
> property works, so I'm a bit puzzled here.
>
> Can you please shed some light on that?
>

I see your point now. It is possible to describe such case in IORT, for 
example:

********************************************
RC0 node:
---------------
Mapping 0:
<input ID range> -> <output ID range>
<0:100> -> <0:100>
parent -> ITS0
---------------
Mapping 1:
<input ID range> -> <output ID range>
<101:200> -> <101:200>
parent -> ITS1
---------------
********************************************

So for this scenario I cannot use pci_host_bridge_acpi_msi_domain() to 
find IRQ domain based on bus device (unless there is only one ITS bound 
to e.g. RC), I should rather add ACPI implementation to 
pci_msi_get_device_domain on per-device MSI basis. Do you agree?

BTW. I should have put IORT specification link to changelog:
http://infocenter.arm.com/help/topic/com.arm.doc.den0049a/DEN0049A_IO_Remapping_Table.pdf

Thanks,
Tomasz