Subject: Re: [PATCH v3 4/7] PCI: Add a new option for resource_alignment to reassign alignment

From: Gavin Shan <[email-masked]>
Date: Fri, 1 Jul 2016 12:25:03 +1000

On Thu, Jun 30, 2016 at 06:53:10PM +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 patch adds a new option "noresize" for the parameter to
>solve this problem.
>
>Signed-off-by: Yongji Xie <[email-masked]>

Reviewed-by: Gavin Shan <[email-masked]>

>---
> Documentation/kernel-parameters.txt |    5 ++++-
> drivers/pci/pci.c                   |   35 +++++++++++++++++++++++++----------
> 2 files changed, 29 insertions(+), 11 deletions(-)
>
>diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>index 82b42c9..c4802f5 100644
>--- a/Documentation/kernel-parameters.txt
>+++ b/Documentation/kernel-parameters.txt
>@@ -2997,13 +2997,16 @@ 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][; ...]
> 				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 6241cfc..1d80a94 100644
>--- a/drivers/pci/pci.c
>+++ b/drivers/pci/pci.c
>@@ -4748,11 +4748,13 @@ 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;
>@@ -4787,6 +4789,11 @@ 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) &&
>@@ -4819,6 +4826,7 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
> {
> 	int i;
> 	struct resource *r;
>+	bool resize = true;
> 	resource_size_t align, size;
>
> 	/* We should never try to reassign VF's alignment */
>@@ -4826,7 +4834,7 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
> 		return;
>
> 	/* 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;
>
>@@ -4848,15 +4856,22 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
> 			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 {
>+			r->flags &= ~IORESOURCE_SIZEALIGN;
>+			r->flags |= IORESOURCE_STARTALIGN | IORESOURCE_UNSET;

			f->flags |= (IORESOURCE_STARTALIGN | IORESOURCE_UNSET);

Yongji, one quick question - when IORESOURCE_UNSET is cleared? If it's not
cleared, is there any unexpected side effects? Thanks.

>+			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