linux-kernel - Re: [PATCH 2/2] acpi based pci gap caluculation v2

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Date:	Wed, 25 Jun 2008 10:49:19 +0800
From:	Zhao Yakui <yakui.zhao@...el.com>
To:	akataria@...are.com
Cc:	lenb@...nel.org, Ingo Molnar <mingo@...e.hu>,
	linux-acpi <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] acpi based pci gap caluculation v2

On Tue, 2008-06-24 at 11:48 -0700, Alok Kataria wrote:
> Evaluates the _CRS object under PCI0 looking for producer resources.
> Then searches the e820 memory space for a gap within these producer resources.
> 
> Allows us to find a gap for the unclaimed pci resources or MMIO resources
> for hotplug devices within the BIOS allowed pci regions.
> 
> v1->v2: Some changes in the print strings.
> 	Also note the prototype for e820_search_gap has changes in this
> 	iteration, but the return value is ignored while calling it over here.
> 
> Signed-off-by: Alok N Kataria <akataria@...are.com>
> 
> Index: linux-x86-tree.git/arch/x86/pci/acpi.c
> ===================================================================
> --- linux-x86-tree.git.orig/arch/x86/pci/acpi.c	2008-06-23 17:24:07.000000000 -0700
> +++ linux-x86-tree.git/arch/x86/pci/acpi.c	2008-06-24 10:57:43.000000000 -0700
> @@ -4,6 +4,7 @@
>  #include <linux/irq.h>
>  #include <linux/dmi.h>
>  #include <asm/numa.h>
> +#include <asm/e820.h>
>  #include "pci.h"
>  
>  struct pci_root_info {
> @@ -14,6 +15,11 @@
>  	int busnum;
>  };
>  
> +struct gap_info {
> +	unsigned long gapstart;
> +	unsigned long gapsize;
> +};
> +
>  static acpi_status
>  resource_to_addr(struct acpi_resource *resource,
>  			struct acpi_resource_address64 *addr)
> @@ -110,6 +116,70 @@
>  	}
>  }
>  
> +static acpi_status search_gap(struct acpi_resource *resource, void *data)
> +{
> +	struct acpi_resource_address64 addr;
> +	acpi_status status;
> +	struct gap_info *gap = data;
> +
> +	status = resource_to_addr(resource, &addr);
> +	if (ACPI_SUCCESS(status) &&
> +	    addr.resource_type == ACPI_MEMORY_RANGE &&
> +	    addr.address_length > gap->gapsize) {
> +		e820_search_gap(&gap->gapstart, &gap->gapsize,
> +				(addr.minimum + addr.translation_offset));
> +	}
> +
> +	return AE_OK;
> +}
> +
> +/*
> + * Search for a hole in the 32 bit address space for PCI to assign MMIO
> + * resources for hotplug or unconfigured resources.
> + * We query the CRS object of the PCI root device to look for possible producer
> + * resources in the tree and consider these while calulating the start address
> + * for this hole.
> + */
> +static void pci_setup_gap(acpi_handle *handle)
> +{
> +	struct gap_info gap;
> +	acpi_status status;
> +
> +	gap.gapstart = 0;
> +	gap.gapsize = 0x400000;
> +
> +	status = acpi_walk_resources(handle, METHOD_NAME__CRS,
> +				     search_gap, &gap);
> +
> +	if (ACPI_SUCCESS(status)) {
> +		unsigned long round;
> +
> +		if (!gap.gapstart) {
> +			printk(KERN_ERR "ACPI: Warning: Cannot find a gap "
> +					"in the 32bit address range for PCI\n"
> +					"ACPI: PCI devices may collide with "
> +					"hotpluggable memory address range\n");
> +		}
> +		/*
> +		 * Round the gapstart, uses the same logic as in
> +		 * e820_gap_setup
> +		 */
> +		round = 0x100000;
> +		while ((gap.gapsize >> 4) > round)
> +			round += round;
> +		/* Fun with two's complement */
> +		pci_mem_start = (gap.gapstart + round) & -round;
> +
> +		printk(KERN_INFO "ACPI: PCI resources should "
> +				"start at %lx (gap: %lx:%lx)\n",
> +				pci_mem_start, gap.gapstart, gap.gapsize);
> +	} else {
> +		printk(KERN_ERR "ACPI: Error while searching for gap in "
> +				"the 32bit address range for PCI\n");
> +	}
> +}
> +
> +
>  static void
>  get_current_resources(struct acpi_device *device, int busnum,
>  			int domain, struct pci_bus *bus)
> @@ -220,6 +290,8 @@
>  
>  	if (bus && (pci_probe & PCI_USE__CRS))
>  		get_current_resources(device, busnum, domain, bus);
> +
> +	pci_setup_gap(device->handle);
>  	return bus;
>  }
It seems reasonable. 
But if the resource obtained from the PCI0 _CRS method is incorrect, we
will get the incorrect pci_mem_start.

At the same time after the patch is applied, pci_mem_start will be
parsed in two different ways. If the result is different, maybe the
incorrect pci_mem_start will be used. 

Best regards.
  Yakui
> 
> 
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