linux-kernel - Re: [PATCH v3 3/4] PCI/MSI: Add helper function pci_msi_domain_get_msi

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Message-ID: <560D6068.6030801@arm.com>
Date:	Thu, 01 Oct 2015 17:33:44 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	David Daney <ddaney@...iumnetworks.com>
CC:	David Daney <ddaney.cavm@...il.com>, linux-kernel@...r.kernel.org,
	Will Deacon <will.deacon@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	Grant Likely <grant.likely@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Frank Rowand <frowand.list@...il.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	David Daney <david.daney@...ium.com>
Subject: Re: [PATCH v3 3/4] PCI/MSI:  Add helper function pci_msi_domain_get_msi_rid().

On 01/10/15 17:13, David Daney wrote:
> On 10/01/2015 02:24 AM, Marc Zyngier wrote:
>> Hi David,
>>
>> On 30/09/15 23:47, David Daney wrote:
>>> From: David Daney <david.daney@...ium.com>
>>>
>>> Add pci_msi_domain_get_msi_rid() to return the MSI requester id (RID).
>>> Initially needed by gic-v3 based systems. It will be used by follow on
>>> patch to drivers/irqchip/irq-gic-v3-its-pci-msi.c
>>>
>>> Initially supports mapping the RID via OF device tree.  In the future,
>>> this could be extended to use ACPI _IORT tables as well.
>>>
>>> Signed-off-by: David Daney <david.daney@...ium.com>
>>> ---
>>>   drivers/pci/msi.c   | 31 +++++++++++++++++++++++++++++++
>>>   include/linux/msi.h |  1 +
>>>   2 files changed, 32 insertions(+)
>>>
>>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>>> index d449714..92b6dc9 100644
>>> --- a/drivers/pci/msi.c
>>> +++ b/drivers/pci/msi.c
>>> @@ -20,6 +20,7 @@
>>>   #include <linux/io.h>
>>>   #include <linux/slab.h>
>>>   #include <linux/irqdomain.h>
>>> +#include <linux/of_irq.h>
>>>
>>>   #include "pci.h"
>>>
>>> @@ -1327,4 +1328,34 @@ struct irq_domain *pci_msi_create_default_irq_domain(struct device_node *node,
>>>
>>>   	return domain;
>>>   }
>>> +
>>> +struct get_mis_id_data {
>>> +	u32	alias;
>>> +};
>>> +
>>> +static int get_msi_id_cb(struct pci_dev *pdev, u16 alias, void *data)
>>> +{
>>> +	struct get_mis_id_data *s = data;
>>> +
>>> +	s->alias = alias;
>>> +	return 0;
>>> +}
>>
>> Why not use a naked u32, since you only have a single field in this
>> structure? Or is it that you are anticipating other fields there?
> 
> In this case, I think using a pointer to u32 is a good idea.  It would 
> simplify the source code somewhat.  Although, I think the generated 
> binary would likely be the same.  I don't foresee adding things to this 
> structure.  If it becomes necessary in the future, we can just go back 
> to using a pointer to a structure.
> 
>>
>>> +/**
>>> + * pci_msi_domain_get_msi_rid - Get the MSI requester id (RID)
>>> + * @domain:	The interrupt domain
>>> + * @pdev:	The PCI device.
>>> + *
>>> + * The RID for a device is formed from the alias, with a firmware
>>> + * supplied mapping applied
>>> + *
>>> + * Returns: The RID.
>>> + */
>>> +u32 pci_msi_domain_get_msi_rid(struct irq_domain *domain, struct pci_dev *pdev)
>>> +{
>>> +	struct get_mis_id_data d;
>>> +
>>> +	d.alias = 0;
>>> +	pci_for_each_dma_alias(pdev, get_msi_id_cb, &d);
>>> +	return of_msi_map_rid(&pdev->dev, domain->of_node, d.alias);
>>
>> Should you check whether domain->of_node is NULL first? I don't think
>> of_msi_map_rid would have any problem with that, but a domain that is
>> not backed by an of_node makes me feel a bit uneasy and would tend to
>> indicate that we're not using DT.
> 
> Yes, that makes sense.  As you observe, I think it probably works as is, 
> but it would be good to make it more clear.  This is especially true 
> when we add ACPI support.  We will want to be clear on which of 
> device-tree or ACPI we are using.
> 
> 
>>
>>> +}
>>>   #endif /* CONFIG_PCI_MSI_IRQ_DOMAIN */
>>> diff --git a/include/linux/msi.h b/include/linux/msi.h
>>> index ad939d0..56e3b76 100644
>>> --- a/include/linux/msi.h
>>> +++ b/include/linux/msi.h
>>> @@ -293,6 +293,7 @@ irq_hw_number_t pci_msi_domain_calc_hwirq(struct pci_dev *dev,
>>>   					  struct msi_desc *desc);
>>>   int pci_msi_domain_check_cap(struct irq_domain *domain,
>>>   			     struct msi_domain_info *info, struct device *dev);
>>> +u32 pci_msi_domain_get_msi_rid(struct irq_domain *domain, struct pci_dev *pdev);
>>>   #endif /* CONFIG_PCI_MSI_IRQ_DOMAIN */
>>>
>>>   #endif /* LINUX_MSI_H */
>>>
>>
>> Otherwise looks good to me.
> 
> I will send what I hope is the final revision of the patches later today.

Excellent. In related news, I've rebased my msi-parent stuff on top of
this series, and extended it to also deal with msi-map for matching MSI
domains.

With the two series, we should now have something vaguely coherent that
deals with both the old version of msi-parent, its new definition, and
msi-map in its whole glory. Fun times!

Thanks,

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