linux-kernel - Re: [PATCH 3/5] PCI: Set PCI_BUS_FLAGS_MSI_REMAP if MSI controller supports IRQ remapping

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Date:	Wed, 25 May 2016 13:48:00 +0800
From:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	iommu@...ts.linux-foundation.org, alex.williamson@...hat.com,
	bhelgaas@...gle.com, aik@...abs.ru, benh@...nel.crashing.org,
	paulus@...ba.org, mpe@...erman.id.au, joro@...tes.org,
	warrier@...ux.vnet.ibm.com, zhong@...ux.vnet.ibm.com,
	nikunj@...ux.vnet.ibm.com, eric.auger@...aro.org,
	will.deacon@....com, gwshan@...ux.vnet.ibm.com,
	David.Laight@...LAB.COM, alistair@...ple.id.au, ruscur@...sell.cc
Subject: Re: [PATCH 3/5] PCI: Set PCI_BUS_FLAGS_MSI_REMAP if MSI controller
 supports IRQ remapping

On 2016/5/25 5:04, Bjorn Helgaas wrote:

> On Wed, Apr 27, 2016 at 08:43:28PM +0800, Yongji Xie wrote:
>> On ARM HW the capability of IRQ remapping is abstracted on
>> MSI controller side. MSI_FLAG_IRQ_REMAPPING is used to advertise
>> this [1].
>>
>> To have a universal flag to test this capability for different
>> archs on PCI side, we set PCI_BUS_FLAGS_MSI_REMAP for PCI buses
>> when MSI_FLAG_IRQ_REMAPPING is set.
>>
>> [1] http://www.spinics.net/lists/kvm/msg130256.html
>>
>> Signed-off-by: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
>> ---
>>   drivers/pci/msi.c   |   12 ++++++++++++
>>   drivers/pci/probe.c |    3 +++
>>   include/linux/msi.h |    6 +++++-
>>   3 files changed, 20 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>> index a080f44..1661cdf 100644
>> --- a/drivers/pci/msi.c
>> +++ b/drivers/pci/msi.c
>> @@ -1134,6 +1134,18 @@ void *msi_desc_to_pci_sysdata(struct msi_desc *desc)
>>   }
>>   EXPORT_SYMBOL_GPL(msi_desc_to_pci_sysdata);
>>   
>> +void pci_bus_check_msi_remapping(struct pci_bus *bus,
>> +				 struct irq_domain *domain)
>> +{
>> +#ifdef CONFIG_PCI_MSI_IRQ_DOMAIN
>> +	struct msi_domain_info *info;
>> +
>> +	info = msi_get_domain_info(domain);
>> +	if (info->flags & MSI_FLAG_IRQ_REMAPPING)
>> +		bus->bus_flags |= PCI_BUS_FLAGS_MSI_REMAP;
>> +#endif
>> +}
> Functions named "check_foo" are a pet peeve of mine because the name
> doesn't tell us anything about what the function *does*.  In this
> case, we know it checks something about MSI remapping, but we don't
> know whether we're checking whether it's enabled, disabled, or some
> other property.
>
> I'd prefer something like:
>
>    int pci_bus_msi_isolated(struct pci_bus *bus, struct irq_domain *domain)
>    {
>      struct msi_domain_info *info;
>
>      if (!domain)
>        return 0;
>
>      info = msi_get_domain_info(domain);
>      if (info->flags & MSI_FLAG_IRQ_REMAPPING)
>        return 1;
>
>      return 0;
>    }
>
>    void pci_set_bus_msi_domain(struct pci_bus *bus)
>    {
>      ...
>      if (b == bus && pci_bus_msi_isolated(bus, d))
>        bus->bus_flags |= PCI_BUS_FLAGS_MSI_REMAP;

Yes. This looks more reasonable. Thank you!

Regards,
Yongji