linux-kernel - Re: [PATCH] pci: support alignments upto 8Gb in pbus_size

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Date:	Wed, 11 Jul 2012 16:53:05 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Nikhil P Rao <nikhil.rao@...el.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH] pci: support alignments upto 8Gb in pbus_size_mem()

On Mon, Jun 25, 2012 at 2:54 PM, Nikhil P Rao <nikhil.rao@...el.com> wrote:
> On Sat, 2012-06-23 at 12:15 -0600, Bjorn Helgaas wrote:
>> On Thu, Jun 21, 2012 at 5:47 PM, Nikhil P Rao <nikhil.rao@...el.com> wrote:
>> > I ran into the "disabling BAR .." error message when
>> > trying to use a 8Gb PCIe card on a system with a BIOS
>> > that didnt have support for BAR size > 2Gb.
>>
>> So the BIOS left the 8Gb BAR unassigned, and you got the "disabling
>> BAR ... (bad alignment)" message when Linux tried to enable it?
>
> Yes.
>
>> How do we know 8Gb is the correct new limit?  Are we going to be
>> fixing this again when we see a 16Gb or a 32Gb BAR?  Do we need a
>> better algorithm that doesn't have a limit like this?
>>
>
> The original error message seems applicable to 32bit archs. and not to
> 64 bit archs. How about the patch below - is aligns[44] (256bytes more)
> acceptable ?
>
>
> From: Nikhil P Rao <nikhil.rao@...el.com>
> Date: Mon, 25 Jun 2012 13:33:55 -0700
> Subject: [PATCH] pci: fix resource size check
>
> Support a PCI BAR alignment of > 2Gb, the original check was
> only applicable to 32 bit kernels,
>
> Signed-off-by: Nikhil P Rao <nikhil.rao@...el.com>
> ---
>  drivers/pci/setup-bus.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 8fa2d4b..9f8d9ea 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -780,7 +780,7 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
>  {
>         struct pci_dev *dev;
>         resource_size_t min_align, align, size, size0, size1;
> -       resource_size_t aligns[12];     /* Alignments from 1Mb to 2Gb */
> +       resource_size_t aligns[44];     /* Alignments from 1Mb to 2^63 */
>         int order, max_order;
>         struct resource *b_res = find_free_bus_resource(bus, type);
>         unsigned int mem64_mask = 0;
> @@ -819,7 +819,8 @@ static int pbus_size_mem(struct pci_bus *bus, unsigned long mask,
>                         /* For bridges size != alignment */
>                         align = pci_resource_alignment(dev, r);
>                         order = __ffs(align) - 20;
> -                       if (order > 11) {
> +                       if ((sizeof(size_t) == 4 && order > 11) ||
> +                                       (sizeof(size_t) == 8 && order > 43)) {
>                                 dev_warn(&dev->dev, "disabling BAR %d: %pR "
>                                          "(bad alignment %#llx)\n", i, r,
>                                          (unsigned long long) align);

Yinghai, what's your opinion on this?  The aligns[] array on the stack
is currently 96 bytes and would grow to 352 with this patch, which
does seem like quite a bit.

I do think the 2GB limit here is out-of-date.

Bjorn
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