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

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Date:	Thu, 22 Oct 2015 13:56:47 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci@...r.kernel.org,
	Ben Shelton <benjamin.h.shelton@...el.com>,
	linux-kernel@...r.kernel.org,
	Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH] PCI: Remove unnecessary re-read of SR-IOV offset/stride
 registers

On Fri, Oct 16, 2015 at 04:16:28PM -0500, Bjorn Helgaas wrote:
> 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>

I haven't seen any objections, so I applied this to pci/virtualization for
v4.4.

> ---
>  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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