linux-kernel - Re: [PATCH V4 4/7] ARM64, ACPI, PCI: I/O Remapping Table (IORT) initial support.

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Message-ID: <570E6B2C.3060700@arm.com>
Date:	Wed, 13 Apr 2016 16:52:12 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Tomasz Nowicki <tn@...ihalf.com>, tglx@...utronix.de,
	jason@...edaemon.net, rjw@...ysocki.net, lorenzo.pieralisi@....com,
	robert.richter@...iumnetworks.com, shijie.huang@....com,
	Suravee.Suthikulpanit@....com, hanjun.guo@...aro.org
Cc:	al.stone@...aro.org, mw@...ihalf.com, graeme.gregory@...aro.org,
	Catalin.Marinas@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, ddaney.cavm@...il.com,
	okaya@...eaurora.org
Subject: Re: [PATCH V4 4/7] ARM64, ACPI, PCI: I/O Remapping Table (IORT)
 initial support.

On 13/04/16 16:36, Tomasz Nowicki wrote:
> On 13.04.2016 17:23, Marc Zyngier wrote:
>> On 04/04/16 09:52, Tomasz Nowicki wrote:
>>> IORT shows representation of IO topology for ARM based systems.
>>> It describes how various components are connected together on
>>> parent-child basis e.g. PCI RC -> SMMU -> ITS. Also see IORT spec.
>>>
>>> Initial support allows to:
>>> - register ITS MSI chip along with ITS translation ID and domain token
>>> - deregister ITS MSI chip based on ITS translation ID
>>> - find registered domain token based on ITS translation ID
>>> - map MSI RID based on PCI device and requester ID
>>> - find domain token based on PCI device and requester ID
>>>
>>> To: Rafael J. Wysocki <rjw@...ysocki.net>
>>> Signed-off-by: Tomasz Nowicki <tn@...ihalf.com>
>>> ---
>>>   drivers/acpi/Kconfig    |   3 +
>>>   drivers/acpi/Makefile   |   1 +
>>>   drivers/acpi/iort.c     | 335 ++++++++++++++++++++++++++++++++++++++++++++++++
>>>   drivers/irqchip/Kconfig |   1 +
>>>   include/linux/iort.h    |  31 +++++
>>>   5 files changed, 371 insertions(+)
>>>   create mode 100644 drivers/acpi/iort.c
>>>   create mode 100644 include/linux/iort.h
>>>
>>
>> [...]
>>
>>> +static acpi_status
>>> +iort_find_dev_callback(struct acpi_iort_node *node, void *context)
>>> +{
>>> +	struct acpi_iort_root_complex *pci_rc;
>>> +	struct device *dev = context;
>>> +	struct pci_bus *bus;
>>> +
>>> +	switch (node->type) {
>>> +	case ACPI_IORT_NODE_PCI_ROOT_COMPLEX:
>>> +		bus = to_pci_bus(dev);
>>> +		pci_rc = (struct acpi_iort_root_complex *)node->node_data;
>>> +
>>> +		/*
>>> +		 * It is assumed that PCI segment numbers maps one-to-one
>>> +		 * with root complexes. Each segment number can represent only
>>> +		 * one root complex.
>>> +		 */
>>> +		if (pci_rc->pci_segment_number == pci_domain_nr(bus))
>>> +			return AE_OK;
>>
>> What guarantees that this is ever valid? As far as I know, pci_domain_nr
>> is completely arbitrary, and depends both on the probe order and the
>> phase of the moon. If you want this to be reliable, you need to allocate
>> the domain number from pci_segment_number.
>>
>> I must be missing something. Care to shed some light on this?
>>
> Sure. Please see:
> http://infocenter.arm.com/help/topic/com.arm.doc.den0049a/DEN0049A_IO_Remapping_Table.pdf
> 3.1.1.5 PCI root complex node
> PCI Segment number -> The PCI segment number, as in MCFG and as
> returned by _SEG in the namespace.
> 
> So IORT spec states that pci_segment_number corresponds to the segment 
> number from MCFG table and _SEG method. Here is my patch which makes 
> sure pci_domain_nr(bus) is set properly:
> https://lkml.org/lkml/2016/2/16/418

Lovely. So this series is actually dependent on the PCI one. I guess we
need to solve that one first, because IORT seems pretty pointless if we
don't have PCI support. What's the plan?

	M.
-- 
Jazz is not dead. It just smells funny...