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From: "Raj, Ashok" <ashok.raj@intel.com>
To: Jason Gunthorpe <jgg@mellanox.com>
Cc: Megha Dey <megha.dey@linux.intel.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"x86@kernel.org" <x86@kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"maz@kernel.org" <maz@kernel.org>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"rafael@kernel.org" <rafael@kernel.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"tglx@linutronix.de" <tglx@linutronix.de>,
	"hpa@zytor.com" <hpa@zytor.com>,
	"alex.williamson@redhat.com" <alex.williamson@redhat.com>,
	"megha.dey@intel.com" <megha.dey@intel.com>,
	"jacob.jun.pan@intel.com" <jacob.jun.pan@intel.com>,
	Ashok Raj <ashok.raj@intel.com>
Subject: Re: [RFC V1 0/7] Add support for a new IMS interrupt mechanism
Date: Fri, 13 Sep 2019 13:27:10 -0700
Message-ID: <20190913202710.GA999@otc-nc-03> (raw)
In-Reply-To: <VI1PR05MB4141EAE19EE47DA20A75AE21CFB30@VI1PR05MB4141.eurprd05.prod.outlook.com>

On Fri, Sep 13, 2019 at 07:50:50PM +0000, Jason Gunthorpe wrote:
> On Thu, Sep 12, 2019 at 06:32:01PM -0700, Megha Dey wrote:
> 
> > This series is a basic patchset to get the ball rolling and receive some
> > inital comments. As per my discussion with Marc Zyngier and Thomas Gleixner
> > at the Linux Plumbers, I need to do the following:
> > 1. Since a device can support MSI-X and IMS simultaneously, ensure proper
> >    locking mechanism for the 'msi_list' in the device structure.
> > 2. Introduce dynamic allocation of IMS vectors perhaps by using a group ID
> > 3. IMS support of a device needs to be discoverable. A bit in the vendor
> >    specific capability in the PCI config is to be added rather than getting
> >    this information from each device driver.
> 
> Why #3? The point of this scheme is to delegate programming the
> addr/data pairs to the driver so it can be done in some
> device-specific way. There is no PCI standard behind this, and no
> change in PCI semantics. 
> 
> I think it would be a tall ask to get a config space bit from PCI-SIG
> for something that has little to do with PCI.

This isn't a standard config capability. Its Designated Vendor Specific
Capability (DVSEC). The device is responsible for managing the addr-data
pair. This provides a hint to the OS framework that this device has
device specific methods.

Agreed its not required, but some OSV's like a generic way to discover
these capabilities, hence its there so device vendors can have
a common guideline.

Check here for some of those details:

https://software.intel.com/en-us/blogs/2018/06/25/introducing-intel-scalable-io-virtualization 

> 
> After seeing that we already have a platform device based version of
> this same idea (drivers/base/platform-msi.c), I think the task here is
> really just to extend and expand that approach to work generically for
> platform and PCI devices. Along the way tidying the arch interface so
> x86 and ARM's stuff to support that uses the same generic interfaces.
> 
> ie it is re-organizing code and ideas already in Linux, not defining
> some new standard.
> 
> I also think refering to this existing idea by some new IMS name is
> only confusing people what the goal is... Which is perhaps why #3 was
> suggested??
> 
> Stated more clearly, I think all uses would be satisfied if
> platform_msi_domain_alloc_irqs() could be called for struct
> pci_device, could be called multiple times for the same struct
> pci_device, and co-existed with MSI and MSI-X on the same pci_device.
> 
> Jason

  reply index

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-13  1:32 Megha Dey
2019-09-13  1:32 ` [RFC V1 1/7] genirq/msi: Differentiate between various MSI based interrupts Megha Dey
2019-09-13  4:40   ` Greg KH
2019-09-13 14:40   ` Jason Gunthorpe
2019-09-26 21:50   ` Bjorn Helgaas
2019-09-13  1:32 ` [RFC V1 2/7] drivers/base: Introduce callbacks for IMS interrupt domain Megha Dey
2019-09-13  4:39   ` Greg KH
2019-09-13 14:50   ` Jason Gunthorpe
2019-09-13  1:32 ` [RFC V1 3/7] x86/ims: Add support for a new IMS irq domain Megha Dey
2019-09-13 14:52   ` Jason Gunthorpe
2019-09-13 22:07   ` Alex Williamson
2019-09-13  1:32 ` [RFC V1 4/7] irq_remapping: New interfaces to support IMS irqdomain Megha Dey
2019-09-13  1:32 ` [RFC V1 5/7] x86/ims: Introduce x86_ims_ops Megha Dey
2019-09-13 14:54   ` Jason Gunthorpe
2019-09-13  1:32 ` [RFC V1 6/7] ims-msi: Add APIs to allocate/free IMS interrupts Megha Dey
2019-09-26 21:44   ` Bjorn Helgaas
2019-09-13  1:32 ` [RFC V1 7/7] ims: Add the set_desc callback Megha Dey
2019-09-26 21:47   ` Bjorn Helgaas
2019-09-13 19:50 ` [RFC V1 0/7] Add support for a new IMS interrupt mechanism Jason Gunthorpe
2019-09-13 20:27   ` Raj, Ashok [this message]
2019-09-19 18:25     ` Jason Gunthorpe

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