linux-kernel - Re: [RESEND PATCH v2 2/4] PCI: Do not Use IORESOURCE

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Message-Id: <522cb95b-349a-f34c-9930-9c3633b62419@linux.vnet.ibm.com>
Date:	Tue, 21 Jun 2016 10:59:51 +0800
From:	Yongji Xie <xyjxie@...ux.vnet.ibm.com>
To:	Bjorn Helgaas <helgaas@...nel.org>
Cc:	nikunj@...ux.vnet.ibm.com, zhong@...ux.vnet.ibm.com,
	linux-doc@...r.kernel.org, aik@...abs.ru,
	linux-pci@...r.kernel.org, corbet@....net,
	linux-kernel@...r.kernel.org, gwshan@...ux.vnet.ibm.com,
	warrier@...ux.vnet.ibm.com, alex.williamson@...hat.com,
	paulus@...ba.org, bhelgaas@...gle.com,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [RESEND PATCH v2 2/4] PCI: Do not Use IORESOURCE_STARTALIGN to
 identify bridge resources

On 2016/6/21 9:50, Bjorn Helgaas wrote:

> On Thu, Jun 02, 2016 at 01:46:49PM +0800, Yongji Xie wrote:
>> Now we use the IORESOURCE_STARTALIGN to identify bridge resources
>> in __assign_resources_sorted(). That's quite fragile. We can't
>> make sure that the PCI devices' resources will not use
>> IORESOURCE_STARTALIGN any more.
> Can you explain this a little more?  I don't quite understand the
> problem.  Maybe you can give an example of the problem?

Now there are two kinds of additional resources in the list: bridge
resource and SR-IOV resource. Here we just want to fix the
additional alignment for bridge. But if SR-IOV resource get the
flag IORESOURCE_STARTALIGN which is not only for bridge, the
current check seems to be wrong. And kernel parameter
"resource_alignment" could set IORESOURCE_STARTALIGN for
SR-IOV resource with my next patch applied.

Thanks,
Yongji

>> In this patch, we try to use a more robust way to identify
>> bridge resources.
>>
>> Signed-off-by: Yongji Xie <xyjxie@...ux.vnet.ibm.com>
>> ---
>>   drivers/pci/setup-bus.c |    9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
>> index 55641a3..216ddbc 100644
>> --- a/drivers/pci/setup-bus.c
>> +++ b/drivers/pci/setup-bus.c
>> @@ -390,6 +390,7 @@ static void __assign_resources_sorted(struct list_head *head,
>>   	struct pci_dev_resource *dev_res, *tmp_res, *dev_res2;
>>   	unsigned long fail_type;
>>   	resource_size_t add_align, align;
>> +	int index;
>>   
>>   	/* Check if optional add_size is there */
>>   	if (!realloc_head || list_empty(realloc_head))
>> @@ -410,11 +411,13 @@ static void __assign_resources_sorted(struct list_head *head,
>>   
>>   		/*
>>   		 * There are two kinds of additional resources in the list:
>> -		 * 1. bridge resource  -- IORESOURCE_STARTALIGN
>> -		 * 2. SR-IOV resource   -- IORESOURCE_SIZEALIGN
>> +		 * 1. bridge resource
>> +		 * 2. SR-IOV resource
>>   		 * Here just fix the additional alignment for bridge
>>   		 */
>> -		if (!(dev_res->res->flags & IORESOURCE_STARTALIGN))
>> +		index = dev_res->res - dev_res->dev->resource;
>> +		if (index < PCI_BRIDGE_RESOURCES ||
>> +			index > PCI_BRIDGE_RESOURCE_END)
> I think the code looks OK; at least, it seems to match the comment.
> I'd just like to understand the problem a little better.
>
>>   			continue;
>>   
>>   		add_align = get_res_add_align(realloc_head, dev_res->res);
>> -- 
>> 1.7.9.5
>>
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