linux-kernel - Re: [PATCH v8 8/9] pci: Add support for creating a generic host

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Message-ID: <20140702173113.GJ24879@arm.com>
Date:	Wed, 2 Jul 2014 18:31:13 +0100
From:	Will Deacon <will.deacon@....com>
To:	Liviu Dudau <Liviu.Dudau@....com>
Cc:	linux-pci <linux-pci@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Arnd Bergmann <arnd@...db.de>,
	linaro-kernel <linaro-kernel@...ts.linaro.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>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Device Tree ML <devicetree@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v8 8/9] pci: Add support for creating a generic
 host_bridge from device tree

On Wed, Jul 02, 2014 at 06:23:55PM +0100, Liviu Dudau wrote:
> On Wed, Jul 02, 2014 at 12:22:30PM +0100, Will Deacon wrote:
> > On Tue, Jul 01, 2014 at 07:43:33PM +0100, Liviu Dudau wrote:
> > > Several platforms use a rather generic version of parsing
> > > the device tree to find the host bridge ranges. Move the common code
> > > into the generic PCI code and use it to create a pci_host_bridge
> > > structure that can be used by arch code.
> > > 
> > > Based on early attempts by Andrew Murray to unify the code.
> > > Used powerpc and microblaze PCI code as starting point.
> > 
> > I just had a quick look at this to see how it differs from the parsing in
> > pci-host-generic.c and there a few small differences worth discussing.

[...]

> > > +	}
> > > +
> > > +	/* Apply architecture specific fixups for the ranges */
> > > +	return pcibios_fixup_bridge_ranges(resources);
> > 
> > I currently mandate at least one non-prefetchable resource in the
> > device-tree. Should I simply drop this restriction, or do I have to somehow
> > hook this into the pcibios callback?
> 
> Don't think I understand why you need at least one non-prefetcheable resource
> but if you want to mandate that then the pcibios_fixup_bridge_ranges() would
> be the place to put that check.

I think it was Arnd's idea at the time:

  http://lists.infradead.org/pipermail/linux-arm-kernel/2014-February/232225.html

and it's probably worth keeping if possible (just to avoid changes to the
behaviour of the existing driver).

However, that means I already need a host-controller callback via
pcibios_fixup_bridge_ranges...

> > > +	err = of_pci_parse_bus_range(parent->of_node, bus_range);
> > > +	if (err) {
> > > +		dev_info(parent, "No bus range for %s, using default [0-255]\n",
> > > +			parent->of_node->full_name);
> > > +		bus_range->start = 0;
> > > +		bus_range->end = 255;
> > > +		bus_range->flags = IORESOURCE_BUS;
> > 
> > What about bus_range->name?
> 
> Don't know! Is anyone using it?

I guess /proc/iomem prints it out? I set it in my current driver, if you
want to take a look.

> > 
> > > +	}
> > > +	busno = bus_range->start;
> > > +	pci_add_resource(&res, bus_range);
> > 
> > I currently truncate the bus range to fit inside the Configuration Space
> > window I have (in the reg property). How can I continue to do that with this
> > patch?
> 
> Not easily. Unless I add an argument to this function that will allow you to
> pass in the max number for the bus range, then the code becomes:
> 
> +	err = of_pci_parse_bus_range(parent->of_node, bus_range);
> +	if (err) {
> +		dev_info(parent, "No bus range for %s, using default [0-%d]\n",
> +			parent->of_node->full_name, max_range);
> +		bus_range->start = 0;
> +		bus_range->end = max_range;
> +		bus_range->flags = IORESOURCE_BUS;
> +	} else {
> +		if (bus_range->end > bus_range->start + max_range) {
> +			bus_range->end = bus_range->start + max_range;
> +		}
> +	}
> 
> Or something like that.

Again, take a look at my driver (it's in mainline now) to see how I deal
with this.

Will
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