linux-kernel - Re: [PATCH v2] PCI: IOV: read SRIOV_NUM

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Message-ID: <20151015175825.GD17702@localhost>
Date:	Thu, 15 Oct 2015 12:58:25 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Ben Shelton <benjamin.h.shelton@...el.com>
Cc:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: IOV: read SRIOV_NUM_VF after enabling ARI

Hi Ben,

On Thu, Oct 08, 2015 at 10:20:17AM -0500, Ben Shelton wrote:
> For some SR-IOV devices, the number of available virtual functions increases
> after enabling ARI.  Currently, SRIOV_NUM_VF is read and saved off before the
> ARI control bit is enabled in SRIOV_CTRL.  This causes an issue when VFs are
> enabled.
> 
> At device init, SRIOV_INITIAL_VF and SRIOV_NUM_VF are specified to contain the
> number of available VFs for the device.  sriov_enable() does a sanity check
> that SRIOV_INITIAL_VF is not greater than iov->total_VFs, the saved-off value
> of SRIOV_NUM_VF.  Since the value of both SRIOV_INITIAL_VF and SRIOV_NUM_VF has
> increased after enabling the ARI bit, the check fails, and the VFs cannot be
> enabled.
> 
> To fix the issue, write SRIOV_CTRL first, and then read SRIOV_NUM_VF.

I think you mean PCI_SRIOV_TOTAL_VR (not NUM_VF), right?

This is interesting because the spec says TotalVFs is HwInit, which
means it's read-only, and it doesn't mention anything about it
changing when ARIis enabled.  I can see why it would change in that
case, so maybe this is just a goof in the spec.

Bjorn

> Signed-off-by: Ben Shelton <benjamin.h.shelton@...el.com>


> ---
> 
> Changes since v1:
>  * Moved read of SRIOV_NUM_VF rather than re-reading it if ARI was enabled.
> 
>  drivers/pci/iov.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index ee0ebff..0174044 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -399,10 +399,6 @@ static int sriov_init(struct pci_dev *dev, int pos)
>  		ssleep(1);
>  	}
>  
> -	pci_read_config_word(dev, pos + PCI_SRIOV_TOTAL_VF, &total);
> -	if (!total)
> -		return 0;
> -
>  	ctrl = 0;
>  	list_for_each_entry(pdev, &dev->bus->devices, bus_list)
>  		if (pdev->is_physfn)
> @@ -414,6 +410,11 @@ static int sriov_init(struct pci_dev *dev, int pos)
>  
>  found:
>  	pci_write_config_word(dev, pos + PCI_SRIOV_CTRL, ctrl);
> +
> +	pci_read_config_word(dev, pos + PCI_SRIOV_TOTAL_VF, &total);
> +	if (!total)
> +		return 0;
> +
>  	pci_write_config_word(dev, pos + PCI_SRIOV_NUM_VF, 0);
>  	pci_read_config_word(dev, pos + PCI_SRIOV_VF_OFFSET, &offset);
>  	pci_read_config_word(dev, pos + PCI_SRIOV_VF_STRIDE, &stride);
> -- 
> 1.9.5
> 
> --
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