linux-kernel - Re: [Patch 1/1] x86 pci: Add option to not assign BAR's if not already assigned

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Message-ID: <4BFFF517.6040401@sgi.com>
Date:	Fri, 28 May 2010 09:53:43 -0700
From:	Mike Travis <travis@....com>
To:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
CC:	x86@...nel.org, Jesse Barnes <jbarnes@...tuousgeek.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Jacob Pan <jacob.jun.pan@...el.com>, Tejun Heo <tj@...nel.org>,
	Mike Habeck <habeck@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Patch 1/1] x86 pci: Add option to not assign BAR's if not already
 assigned

Any further consideration for this patch, or has it been rejected?

Thanks, Mike

Mike Travis wrote:
> Subject: [Patch 1/1] x86 pci: Add option to not assign BAR's if not 
> already assigned
> From: Mike Habeck <habeck@....com>
> 
> The Linux kernel assigns BARs that a BIOS did not assign, most likely
> to handle broken BIOSes that didn't enumerate the devices correctly.
> On UV the BIOS purposely doesn't assign I/O BARs for certain devices/
> drivers we know don't use them (examples, LSI SAS, Qlogic FC, ...).
> We purposely don't assign these I/O BARs because I/O Space is a very
> limited resource.  There is only 64k of I/O Space, and in a PCIe
> topology that space gets divided up into 4k chucks (this is due to
> the fact that a pci-to-pci bridge's I/O decoder is aligned at 4k)...
> Thus a system can have at most 16 cards with I/O BARs: (64k / 4k = 16)
> 
> SGI needs to scale to >16 devices with I/O BARs.  So by not assigning
> I/O BARs on devices we know don't use them, we can do that (iff the
> kernel doesn't go and assign these BARs that the BIOS purposely didn't
> assign).
> 
> This patch will not assign a resource to a device BAR if that BAR was
> not assigned by the BIOS, and the kernel cmdline option 'pci=nobar'
> was specified.   This patch is closely modeled after the 'pci=norom'
> option that currently exists in the tree.
> 
> Signed-off-by: Mike Habeck <habeck@....com>
> Signed-off-by: Mike Travis <travis@....com>
> ---
> Documentation/kernel-parameters.txt |    2 ++
> arch/x86/include/asm/pci_x86.h      |    1 +
> arch/x86/pci/common.c               |   20 ++++++++++++++++++++
> 3 files changed, 23 insertions(+)
> 
> --- linux.orig/Documentation/kernel-parameters.txt
> +++ linux/Documentation/kernel-parameters.txt
> @@ -1935,6 +1935,8 @@ and is between 256 and 4096 characters.
>         norom        [X86] Do not assign address space to
>                 expansion ROMs that do not already have
>                 BIOS assigned address ranges.
> +        nobar        [X86] Do not assign address space to the
> +                BARs that weren't assigned by the BIOS.
>         irqmask=0xMMMM    [X86] Set a bit mask of IRQs allowed to be
>                 assigned automatically to PCI devices. You can
>                 make the kernel exclude IRQs of your ISA cards
> --- linux.orig/arch/x86/include/asm/pci_x86.h
> +++ linux/arch/x86/include/asm/pci_x86.h
> @@ -30,6 +30,7 @@
> #define PCI_HAS_IO_ECS        0x40000
> #define PCI_NOASSIGN_ROMS    0x80000
> #define PCI_ROOT_NO_CRS        0x100000
> +#define PCI_NOASSIGN_BARS    0x200000
> 
> extern unsigned int pci_probe;
> extern unsigned long pirq_table_addr;
> --- linux.orig/arch/x86/pci/common.c
> +++ linux/arch/x86/pci/common.c
> @@ -125,6 +125,23 @@ void __init dmi_check_skip_isa_align(voi
> static void __devinit pcibios_fixup_device_resources(struct pci_dev *dev)
> {
>     struct resource *rom_r = &dev->resource[PCI_ROM_RESOURCE];
> +    struct resource *bar_r;
> +    int bar;
> +
> +    if (pci_probe & PCI_NOASSIGN_BARS) {
> +        /*
> +        * If the BIOS did not assign the BAR, zero out the
> +        * resource so the kernel doesn't attmept to assign
> +        * it later on in pci_assign_unassigned_resources
> +        */
> +        for (bar = 0; bar <= PCI_STD_RESOURCE_END; bar++) {
> +            bar_r = &dev->resource[bar];
> +            if (bar_r->start == 0 && bar_r->end != 0) {
> +                bar_r->flags = 0;
> +                bar_r->end = 0;
> +            }
> +        }
> +    }
> 
>     if (pci_probe & PCI_NOASSIGN_ROMS) {
>         if (rom_r->parent)
> @@ -509,6 +526,9 @@ char * __devinit  pcibios_setup(char *st
>     } else if (!strcmp(str, "norom")) {
>         pci_probe |= PCI_NOASSIGN_ROMS;
>         return NULL;
> +    } else if (!strcmp(str, "nobar")) {
> +        pci_probe |= PCI_NOASSIGN_BARS;
> +        return NULL;
>     } else if (!strcmp(str, "assign-busses")) {
>         pci_probe |= PCI_ASSIGN_ALL_BUSSES;
>         return NULL;
--
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