linux-kernel - Re: [RFC 0/2] PCI: Introduce MSI chip infrastructure

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Message-ID: <20130325093847.7474dc0e@skate>
Date:	Mon, 25 Mar 2013 09:38:47 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Thierry Reding <thierry.reding@...onic-design.de>
Cc:	Andrew Murray <andrew.murray@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/2] PCI: Introduce MSI chip infrastructure

Dear Thierry Reding,

Thanks for your feedback!

On Mon, 25 Mar 2013 08:58:10 +0100, Thierry Reding wrote:

> That sounds very much like one of the use-cases that were discussed. The
> easiest solution would probably be to add an API to look up an MSI chip
> from a DT phandle, so that the PCIe controller's device node could have
> it as a property, somewhat like this:
> 
> 	msi: interrupt-controller {
> 	};
> 
> 	pcie-controller {
> 		...
> 		marvell,msi = <&msi>;
> 		...
> 	};

I'm not sure how to handle this msi interrupt controller with the main
interrupt controller. For now, I have:

        mpic: interrupt-controller@...20000 {
              reg = <0xd0020a00 0x2d0>,
                    <0xd0021070 0x58>;
        };

	[...]

	soc {
                interrupt-parent = <&mpic>;
		[...]
	};

And the MSI interrupt controller shares the same registers as the MPIC.
So should it be something like:

	interrupt-controller {
		reg = <0xd0020a00 0x2d0>,
                    <0xd0021070 0x58>;

		mpic {
			/* Not sure what to have here */
		};

		msi {

			/* Here either */
		};
	};

	soc {
                interrupt-parent = <&mpic>;

		pcie-controller {
			marvell,msi = <&msi>;
		};
	};

Or some other idea?

> Then add some basic infrastructure to register the MSI chip with a
> global list, call that from the interrupt controller initialization:
> 
> 	...
> 	msi_chip_add(&msi);
> 	...
> 
> And finally look it up from the PCIe controller driver:
> 
> 	node = of_parse_phandle(dev->of_node, "marvell,msi", 0);
> 	if (node)
> 		msi = of_find_msi_chip_by_node(node);
> 
> That's roughly what other subsystems do. I wrote something similar once
> for backlight devices, though the registration step (msi_chip_add)
> wasn't necessary there since backlight devices all go into a common
> struct class so class_find_device() can be used instead of going through
> a separate registry.

Ok, that part sounds good to me. I'm still unsure about the DT
representation, though (see above), and experience has shown that's
it's a pretty good idea to discuss a little bit the DT representation
before going on with some code :)

Thanks again for your feedback!

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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