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

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

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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