linux-kernel - Re: [PATCH v8 3/9] pci: Introduce pci_register_io

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Message-ID: <20140702112222.GK18731@arm.com>
Date:	Wed, 2 Jul 2014 12:22:22 +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 3/9] pci: Introduce pci_register_io_range() helper
 function.

On Tue, Jul 01, 2014 at 07:43:28PM +0100, Liviu Dudau wrote:
> Some architectures do not have a simple view of the PCI I/O space
> and instead use a range of CPU addresses that map to bus addresses. For
> some architectures these ranges will be expressed by OF bindings
> in a device tree file.
> 
> Introduce a pci_register_io_range() helper function with a generic
> implementation that can be used by such architectures to keep track
> of the I/O ranges described by the PCI bindings. If the PCI_IOBASE
> macro is not defined that signals lack of support for PCI and we
> return an error.

[...]

> +/*
> + * Record the PCI IO range (expressed as CPU physical address + size).
> + * Return a negative value if an error has occured, zero otherwise
> + */
> +int __weak pci_register_io_range(phys_addr_t addr, resource_size_t size)
> +{
> +#ifdef PCI_IOBASE
> +	struct io_range *res;
> +	resource_size_t allocated_size = 0;
> +
> +	/* check if the range hasn't been previously recorded */
> +	list_for_each_entry(res, &io_range_list, list) {
> +		if (addr >= res->start && addr + size <= res->start + size)
> +			return 0;
> +		allocated_size += res->size;
> +	}
> +
> +	/* range not registed yet, check for available space */
> +	if (allocated_size + size - 1 > IO_SPACE_LIMIT)
> +		return -E2BIG;
> +
> +	/* add the range to the list */
> +	res = kzalloc(sizeof(*res), GFP_KERNEL);
> +	if (!res)
> +		return -ENOMEM;
> +
> +	res->start = addr;
> +	res->size = size;
> +
> +	list_add_tail(&res->list, &io_range_list);
> +
> +	return 0;

Hopefully a stupid question, but how is this serialised? I'm just surprised
that adding to and searching a list are sufficient, unless there's a big
lock somewhere.

Will
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