linux-kernel - Re: [BUGFIX][PATCH] pci: check for 4k resource_size alignment in sriov

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Message-ID: <20120131174402.GA6172@dirshya.in.ibm.com>
Date:	Tue, 31 Jan 2012 23:14:02 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Ram Pai <linuxram@...ibm.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Yinghai Lu <yinghai.lu@...cle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [BUGFIX][PATCH] pci: check for 4k resource_size alignment in
 sriov_init

* Ram Pai <linuxram@...ibm.com> [2012-01-30 11:18:45]:

> On Sat, Jan 28, 2012 at 12:40:32AM +0530, Vaidyanathan Srinivasan wrote:
> > Hi Ram and Jesse,
> > 
> > I found a trivial issue with page size alignment check on IBM POWER
> > box with 64k base page size.  In sriov_init(), changing the check from
> > PAGE_SIZE (arch and config dependent) to HW_PAGE_SIZE (always 4k) was
> > required to use one of the sriov adapter as PF since the
> > resource_size() comes up as 0x8000 and PAGE_SIZE would be 0x10000 for
> > pseries boxes.
> > 
> > I think resource_size() could be less than SystemPageSize, but I would
> > like your comments/ack/nack on any consequences of checking for only
> > 4k alignment here in a system with larger base page size.
> 
> As per the SRIOV specs, the  resource has to be System page size aligned.
> 
> PFs are required to support 4-KB, 8-KB, 64-KB, 256-KB, 1-MB, and 4-MB
> page sizes. In your case if your adapter's PF is not supporting 64K page size
> then I think it is not conforming to the PCI SRIOV spec.

Hi Ram,

Thanks for the pointer.  I did some more experiments and found that
the card does support 64k page size, but the PCI_SRIOV_SYS_PGSIZE was
set to default 4k when we do the query and check resource_size().

You were correct, the resource_size() has to come up with 64k on 64k
PAGE_SIZE system.  We should not change that check.  I was able to
get a working solution by setting PCI_SRIOV_SYS_PGSIZE to 64k before
we do the query.

This was the case in the original code before you moved these to
sriov_enable().  If it is ok to leave the SYS_PGSIZE setting in
sriov_init(), then I have the following fix that works for me.

Please review and let me know your comments.

Thanks,
Vaidy
---

    	pci: set pci sriov page size before reading sriov bar
    
    	For an SRIOV device, PCI_SRIOV_SYS_PGSIZE should be set before
    	the PCI_SRIOV_BAR is queried.  The sys pagesize defaults to 4k,
    	so this change is required on powerpc box with 64k base page size.
    
    	This is a regression caused due to moving SRIOV init to sriov_enable().
    
    	| commit afd24ece5c76af87f6fc477f2747b83a764f161c
    	| Author: Ram Pai <linuxram@...ibm.com>
    
    	| PCI: delay configuration of SRIOV capability
    	| The SRIOV capability, namely page size and total_vfs of a device are
    	| configured during enumeration phase of the device.  This can potentially
    	| interfere with the PCI operations of the platform, if the IOV capability
    	| of the device is not enabled.
    
    Signed-off-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 0321fa3..0dab5ec 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -347,8 +347,6 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 			return rc;
 	}
 
-	pci_write_config_dword(dev, iov->pos + PCI_SRIOV_SYS_PGSIZE, iov->pgsz);
-
 	iov->ctrl |= PCI_SRIOV_CTRL_VFE | PCI_SRIOV_CTRL_MSE;
 	pci_cfg_access_lock(dev);
 	pci_write_config_word(dev, iov->pos + PCI_SRIOV_CTRL, iov->ctrl);
@@ -466,6 +464,7 @@ found:
 		return -EIO;
 
 	pgsz &= ~(pgsz - 1);
+	pci_write_config_dword(dev, pos + PCI_SRIOV_SYS_PGSIZE, pgsz);
 
 	nres = 0;
 	for (i = 0; i < PCI_SRIOV_NUM_BARS; i++) {

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