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

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Date:	Mon, 25 Jun 2012 13:54:47 -0700
From:	Nikhil P Rao <nikhil.rao@...el.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] pci: support alignments upto 8Gb in pbus_size_mem()

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);
-- 
1.7.1

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