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

[Yongji Xie <xyjxie@linux.vnet.ibm.com>]

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@linux.vnet.ibm.com>
> Reviewed-by: Gavin Shan <gwshan@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 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