linux-kernel - [PATCH] PCI: Remove unnecessary re-read of SR-IOV offset/stride registers

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Date:	Fri, 16 Oct 2015 16:16:28 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	linux-pci@...r.kernel.org
Cc:	Ben Shelton <benjamin.h.shelton@...el.com>,
	linux-kernel@...r.kernel.org,
	Alexander Duyck <alexander.duyck@...il.com>
Subject: [PATCH] PCI: Remove unnecessary re-read of SR-IOV offset/stride
 registers

Previously, we read PCI_SRIOV_VF_OFFSET and PCI_SRIOV_VF_STRIDE from the
SR-IOV capability in pci_iov_set_numvfs() after changing PCI_SRIOV_NUM_VF,
and we read them again in sriov_enable().  But sriov_init() always calls
pci_iov_set_numvfs() before a successful return, and it caches the offset
and stride values, so there's no need to read the capability again in
sriov_enable().

Remove the PCI_SRIOV_VF_OFFSET and PCI_SRIOV_VF_STRIDE config reads from
sriov_enable() and use the cached values from the pci_sriov structure.

Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
---
 drivers/pci/iov.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 0202ab0..9b52ad4 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -230,7 +230,7 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	int rc;
 	int i, j;
 	int nres;
-	u16 offset, stride, initial;
+	u16 initial;
 	struct resource *res;
 	struct pci_dev *pdev;
 	struct pci_sriov *iov = dev->sriov;
@@ -253,9 +253,7 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 	    (!(iov->cap & PCI_SRIOV_CAP_VFM) && (nr_virtfn > initial)))
 		return -EINVAL;
 
-	pci_read_config_word(dev, iov->pos + PCI_SRIOV_VF_OFFSET, &offset);
-	pci_read_config_word(dev, iov->pos + PCI_SRIOV_VF_STRIDE, &stride);
-	if (!offset || (nr_virtfn > 1 && !stride))
+	if (!iov->offset || (nr_virtfn > 1 && !iov->stride))
 		return -EIO;
 
 	nres = 0;
@@ -270,9 +268,6 @@ static int sriov_enable(struct pci_dev *dev, int nr_virtfn)
 		return -ENOMEM;
 	}
 
-	iov->offset = offset;
-	iov->stride = stride;
-
 	bus = pci_iov_virtfn_bus(dev, nr_virtfn - 1);
 	if (bus > dev->bus->busn_res.end) {
 		dev_err(&dev->dev, "can't enable %d VFs (bus %02x out of range of %pR)\n",

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