Re: [RESEND PATCH v2 3/4] PCI: Add a new option for resource_alignment to reassign alignment

Yongji Xie
2016-06-21T03:28:43Z

On 2016/6/21 9:57, Bjorn Helgaas wrote:

> On Thu, Jun 02, 2016 at 01:46:50PM +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.
> Why do we ever want to change the resource's size? I understand that
> you want to change the resource's *alignment*, and that part makes
> sense. But why change the *size*? Changing the resource size doesn't
> change the hardware BAR size; it just means the struct resource will
> describe a region larger than what the BAR actually claims. That
> unnecessarily wastes space after the BAR.
>
> This was a problem with the code even before your patch; I'm
> suggesting that if you have a way to change the alignment without
> changing the resource size, maybe we should do that all the time.
> Then you wouldn't need to add the "noresize" option.

Yes, changing resource's size seems not a good idea. But
would it break some existing systems which are using this
kernel parameter if we remove the "noresize" option and change
the alignment all the time?

Thanks,
Yongji

>> Signed-off-by: Yongji Xie <xyjxie@linux.vnet.ibm.com>
>> ---
>> 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 a259394..3ee13e5 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;
>> @@ -4786,6 +4788,11 @@ 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) &&
>> @@ -4818,11 +4825,12 @@ 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;
>>
>> @@ -4844,15 +4852,22 @@ 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 {
>> + r->flags &= ~IORESOURCE_SIZEALIGN;
>> + r->flags |= IORESOURCE_STARTALIGN | IORESOURCE_UNSET;
>> + 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
>> --
>> 1.7.9.5
>>
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