On Tue, Apr 05, 2016 at 09:43:31PM +0800, Yongji Xie wrote:

When using resource_alignment kernel parameter,
the current implement reassigns the alignment by
changing resources' size which can potentially
break some drivers. For example, the driver uses
the size to locate some register whose length is
related to the size.

This adds a new option "noresize" for the
parameter to solve this problem.

Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
---
Documentation/kernel-parameters.txt |    5 ++++-
drivers/pci/pci.c                   |   37 +++++++++++++++++++++++++----------
2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9a53c92..d8b29ab 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2912,13 +2912,16 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
				window. The default value is 64 megabytes.
		resource_alignment=
				Format:
-				[<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
+				[<order of align>@][<domain>:]<bus>:<slot>.<func>
+				[:noresize][; ...]

If I'm correct enough, it breaks existing application using this interface. "noresize"
would be a optinal parallel property to "align". So the string would have below format
if nobody else objects:

	order,noresize@domain:bus:slot.func

				Specifies alignment and device to reassign
				aligned memory resources.
				If <order of align> is not specified,
				PAGE_SIZE is used as alignment.
				PCI-PCI bridge can be specified, if resource
				windows need to be expanded.
+				noresize: Don't change the resources' sizes when
+				reassigning alignment.
		ecrc=		Enable/disable PCIe ECRC (transaction layer
				end-to-end CRC checking).
				bios: Use BIOS/firmware settings. This is the
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 1db9267..7271ce3 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4594,11 +4594,13 @@ static DEFINE_SPINLOCK(resource_alignment_lock);
/**
 * pci_specified_resource_alignment - get resource alignment specified by user.
 * @dev: the PCI device to get
+ * @resize: whether or not to change resources' size when reassigning alignment
 *
 * RETURNS: Resource alignment if it is specified.
 *          Zero if it is not specified.
 */
-static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev)
+static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
+		bool *resize)
{
	int seg, bus, slot, func, align_order, count;
	resource_size_t align = 0;
@@ -4632,6 +4634,11 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev)
			}
		}
		p += count;
+		if (!strncmp(p, ":noresize", 9)) {
+			*resize = false;
+			p += 9;
+		} else
+			*resize = true;
		if (seg == pci_domain_nr(dev->bus) &&
			bus == dev->bus->number &&
			slot == PCI_SLOT(dev->devfn) &&
@@ -4664,11 +4671,12 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
{
	int i;
	struct resource *r;
+	bool resize = true;
	resource_size_t align, size;
	u16 command;

	/* check if specified PCI is target device to reassign */
-	align = pci_specified_resource_alignment(dev);
+	align = pci_specified_resource_alignment(dev, &resize);
	if (!align)
		return;

@@ -4690,15 +4698,24 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
		if (!(r->flags & IORESOURCE_MEM))
			continue;
		size = resource_size(r);
-		if (size < align) {
-			size = align;
-			dev_info(&dev->dev,
-				"Rounding up size of resource #%d to %#llx.\n",
-				i, (unsigned long long)size);
+		if (resize) {
+			if (size < align) {
+				size = align;
+				dev_info(&dev->dev,
+					"Rounding up size of resource #%d to %#llx.\n",
+					i, (unsigned long long)size);
+			}
+			r->flags |= IORESOURCE_UNSET;
+			r->end = size - 1;
+			r->start = 0;
+		} else {
+			if (size > align)
+				align = size;
+			r->flags &= ~IORESOURCE_SIZEALIGN;
+			r->flags |= IORESOURCE_STARTALIGN | IORESOURCE_UNSET;
+			r->start = align;
+			r->end = r->start + size - 1;

It could be something like below if you like:

			r->start = max(align, size);
			r->end = r->start + size - 1;

		}
-		r->flags |= IORESOURCE_UNSET;
-		r->end = size - 1;
-		r->start = 0;
	}
	/* Need to disable bridge's resource window,
	 * to enable the kernel to reassign new resource

Thanks,
Gavin

-- 
1.7.9.5

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