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

[Yongji Xie]

Hi Gavin,

On 2016/7/1 10:25, Gavin Shan wrote:

> 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 <xyjxie@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Gavin Shan <gwshan@xxxxxxxxxxxxxxxxxx>
>
> > ---
> > 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.

PCI core will clear this flag in pci_assign_resource() when the BAR
has been assigned properly. If it's not cleared, the driver will fail in
binding the device because pci_enable_resources() will check this flag.

Thanks,
Yongji