linux-kernel - Re: [PATCH 1/2] PCI/IOV: Add function to allow Function Dependency Link override.

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Date:   Mon, 22 Aug 2016 09:36:37 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Omer Khaliq <okhaliq@...iumnetworks.com>
Cc:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-arm-kernel@...r.kernel.org,
        bhelgaas@...gle.com, mpm@...enic.com, herbert@...dor.apana.org.au,
        Ananth.Jasty@...ium.com, david.daney@...ium.com
Subject: Re: [PATCH 1/2] PCI/IOV: Add function to allow Function Dependency
 Link override.

Hi David & Omer,

On Fri, Aug 19, 2016 at 03:32:12PM -0700, Omer Khaliq wrote:
> From: David Daney <david.daney@...ium.com>
> 
> Some hardware presents an incorrect SR-IOV Function Dependency Link,
> add a function to allow this to be overridden in the PF driver for
> such devices.
> 
> Signed-off-by: David Daney <david.daney@...ium.com>
> Signed-off-by: Omer Khaliq <okhaliq@...iumnetworks.com>
> ---
>  drivers/pci/iov.c   | 14 ++++++++++++++
>  include/linux/pci.h |  1 +
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> index 2194b44..81f0672 100644
> --- a/drivers/pci/iov.c
> +++ b/drivers/pci/iov.c
> @@ -640,6 +640,20 @@ int pci_enable_sriov(struct pci_dev *dev, int nr_virtfn)
>  EXPORT_SYMBOL_GPL(pci_enable_sriov);
>  
>  /**
> + * pci_sriov_fdl_override - fix incorrect Function Dependency Link
> + * @dev: the PCI device
> + * @fdl: the corrected Function Dependency Link value
> + *
> + * For hardware presenting an incorrect Function Dependency Link in
> + * the SR-IOV Extended Capability, allow a driver to override it.
> + */
> +void pci_sriov_fdl_override(struct pci_dev *dev, u8 fdl)
> +{
> +	dev->sriov->link = fdl;
> +}
> +EXPORT_SYMBOL_GPL(pci_sriov_fdl_override);

We usually use quirks to work around problems in config space.  That's
a nice mechanism because we don't have to add new PCI core interfaces
and it makes it clear that we're working around a hardware problem.

Can you use a quirk here?  We allocate dev->sriov in the
pci_init_capabilities() path, so it looks like a pci_fixup_final quirk
should work.

> +
> +/**
>   * pci_disable_sriov - disable the SR-IOV capability
>   * @dev: the PCI device
>   */
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 2599a98..da8a5b3 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1823,6 +1823,7 @@ int pci_num_vf(struct pci_dev *dev);
>  int pci_vfs_assigned(struct pci_dev *dev);
>  int pci_sriov_set_totalvfs(struct pci_dev *dev, u16 numvfs);
>  int pci_sriov_get_totalvfs(struct pci_dev *dev);
> +void pci_sriov_fdl_override(struct pci_dev *dev, u8 fdl);
>  resource_size_t pci_iov_resource_size(struct pci_dev *dev, int resno);
>  #else
>  static inline int pci_iov_virtfn_bus(struct pci_dev *dev, int id)
> -- 
> 1.9.1
> 
> --
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