Subject: Re: [RFC v5 3/7] PCI: Add a new option for resource_alignment to reassign alignment

From: Yongji Xie <[email-masked]>
Date: Wed, 6 Apr 2016 10:43:57 +0800

On 2016/4/6 9:43, Gavin Shan wrote:
> On Tue, Apr 05, 2016 at 09:43:31PM +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 adds a new option "noresize" for the
>> parameter to solve this problem.
>>
>> Signed-off-by: Yongji Xie <[email-masked]>
>> ---
>> Documentation/kernel-parameters.txt |    5 ++++-
>> drivers/pci/pci.c                   |   37 +++++++++++++++++++++++++----------
>> 2 files changed, 31 insertions(+), 11 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 9a53c92..d8b29ab 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -2912,13 +2912,16 @@ 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][; ...]
> If I'm correct enough, it breaks existing application using this interface. "noresize"
> would be a optinal parallel property to "align". So the string would have below format
> if nobody else objects:
>
> 	order,noresize@domain:bus:slot.func

Sorry. I don't get your point. Why [:noresize] would break
existing application using this interface? Doesn't
[:noresize] mean an optional property?

[<order of align>@] is also an optional property.
Sometimes, we would not specify it. So we should
not put "noresize" into [<order of align>@] in case
that we want to use "noresize" but we don't want
to specify <order of align>.

>
>> 				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 1db9267..7271ce3 100644
>> --- a/drivers/pci/pci.c
>> +++ b/drivers/pci/pci.c
>> @@ -4594,11 +4594,13 @@ 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;
>> @@ -4632,6 +4634,11 @@ 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) &&
>> @@ -4664,11 +4671,12 @@ 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;
>>
>> @@ -4690,15 +4698,24 @@ 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 {
>> +			if (size > align)
>> +				align = size;
>> +			r->flags &= ~IORESOURCE_SIZEALIGN;
>> +			r->flags |= IORESOURCE_STARTALIGN | IORESOURCE_UNSET;
>> +			r->start = align;
>> +			r->end = r->start + size - 1;
> It could be something like below if you like:
>
> 			r->start = max(align, size);
> 			r->end = r->start + size - 1;

Sounds good!

Thanks,
Yongji

>> 		}
>> -		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
>
>> -- 
>> 1.7.9.5
>>
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