linux-kernel - Re: [PATCH v10 00/10] Support for creating generic PCI host bridges from DT

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Message-ID: <20140912093018.GX27864@e106497-lin.cambridge.arm.com>
Date:	Fri, 12 Sep 2014 10:30:18 +0100
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
	Rob Herring <robh+dt@...nel.org>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....com>,
	Russell King <linux@....linux.org.uk>,
	linux-pci <linux-pci@...r.kernel.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Tanmay Inamdar <tinamdar@....com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Sinan Kaya <okaya@...eaurora.org>,
	Jingoo Han <jg1.han@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	linux-arch <linux-arch@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Device Tree ML <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v10 00/10] Support for creating generic PCI host bridges
 from DT

On Fri, Sep 12, 2014 at 09:25:13AM +0100, Suravee Suthikulpanit wrote:
> On 9/8/2014 8:54 AM, Liviu Dudau wrote:
> > This is my version 10 of the attempt at adding support for generic PCI host
> > bridge controllers that make use of device tree information to
> > configure themselves. This version reverses v9's attempt to create one function
> > to drive the whole process of extracting the host bridge ranges, setup the
> > host bridge driver and then scan the root bus behind the host bridge. While it
> > would've been quite user friendly, I agree that it would've caused a lot of pain
> > in the future.
> >
> > I would like to get ACKs for the remaining patches as I would like to integrate
> > this into -next in the following week.
> >
> > This version marks an implementation break with the previous versions as
> > of_create_pci_host_bridge() is now gone. It gets replaced by
> > of_pci_get_host_bridge_resources() that only parses the DT and extracts the
> > relevant ranges and converts them to resources. The updated host bridge drivers
> > will have to follow the guidelines in this example code:
> >
> > static int foohb_probe(struct platform_device *pdev)
> > {
> > 	struct device_node *dn = pdev->dev.of_node;
> > 	struct foohb_drv *drv;
> > 	resource_size_t io_base = 0;  /* phys address for start of IO */
> > 	struct pci_bus *bus;
> > 	int err = 0;
> > 	LIST_HEAD(res);
> >
> > 	.....
> > 	err = of_pci_get_host_bridge_resources(dn, 0, 255, &res, &io_base);
> > 	if (err)
> > 		goto err_handling;
> > 	err = foohb_setup(drv, ...., &res, &io_base);
> > 	if (err)
> > 		goto err_handling;

Hi Suravee,

> 
> My understanding is that the "foohb_setup" above is supposed to be equivalent
> to the "int (*setup)(struct pci_host_bridge *, resource_size_t)" in V9 that was
> passed in as an argument of "of_create_pci_hot_bridge()".

Correct. Parameters are probably different, but it is internal to your driver so
you can do whatever you want there.

> 
> The problem I have is I need an intermediate step between "pci_create_root_bus()"
> and "pci_scan_child_bus()" in order to update the information such as the "pci_bus->msi"
> before this is propagate down to the child bus during the "pci_scan_child_bus"
> which is also called in the pci_scan_root_bus() function.

How did that work with my v9 patchset? How does it work for other MSI-aware platforms?
Are they not using pci_scan_child_bus()?

> 
> Does this mean that I should not be calling the pci_scan_root_bus(), and tries to
> re-implement the same logic in my driver?

Bjorn can comment here, but there seems to be a long standing desire to make
pci_scan_root_bus() more useful. If your change is generic enough, how about proposing
a patch for pci_scan_root_bus() and see what feedback you get.

Judging by the complete silence I'm getting on my change (patch 9/10) of the same function,
we might be lucky enough and no one will notice ;) (Bjorn, I'm kidding and I know you
are busy).

Best regards,
Liviu

> 
> Thanks,
> 
> Suravee
> 
> > 	.....
> > 	pci_add_flags(....);
> > 	bus = pci_scan_root_bus(&pdev->dev, 0, &foohb_ops, drv, &res);
> > 	if (!bus)
> > 		goto err_handling;
> > 	....
> > 	return 0;
> >
> > err_handling:
> > 	......
> > 	return err;
> > }
> >
> 
> 
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

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