linux-kernel - Re: [PATCH V3 1/2] Drivers/PCI: Export pcie_has

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Date:   Fri, 8 Dec 2017 14:24:24 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Govinda Tatti <Govinda.Tatti@...cle.COM>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, bhelgaas@...gle.com,
        boris.ostrovsky@...cle.COM, jgross@...e.com, JBeulich@...e.com,
        roger.pau@...rix.com, konrad.wilk@...cle.COM
Subject: Re: [PATCH V3 1/2] Drivers/PCI: Export pcie_has_flr() interface

On Thu, Dec 07, 2017 at 05:21:44PM -0500, Govinda Tatti wrote:
> This patch exports pcie_has_flr() and it is being used by Xen pciback
> driver to reset (flr/slot/bus) PCI devices based on 'reset' SysFS
> attribute.
> 
> Signed-off-by: Govinda Tatti <Govinda.Tatti@...cle.COM>
> ---
> v3: -New
> 
>  drivers/pci/pci.c   | 3 ++-
>  include/linux/pci.h | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 6078dfc..499e922 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3872,7 +3872,7 @@ static void pci_flr_wait(struct pci_dev *dev)
>   * Returns true if the device advertises support for PCIe function level
>   * resets.
>   */
> -static bool pcie_has_flr(struct pci_dev *dev)
> +bool pcie_has_flr(struct pci_dev *dev)
>  {
>  	u32 cap;
>  
> @@ -3882,6 +3882,7 @@ static bool pcie_has_flr(struct pci_dev *dev)
>  	pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &cap);
>  	return cap & PCI_EXP_DEVCAP_FLR;
>  }
> +EXPORT_SYMBOL_GPL(pcie_has_flr);

I'd rather change pcie_flr() so you could *always* call it, and it
would return 0, -ENOTTY, or whatever, based on whether FLR is
supported.  Is that feasible?

I don't like the "Can I do this? Ok, do this" style of interfaces.
It's racy (not really applicable in this case) and seems clunky.

>  /**
>   * pcie_flr - initiate a PCIe function level reset
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index d16a7c0..44bf2b5 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1089,6 +1089,7 @@ int pcie_get_mps(struct pci_dev *dev);
>  int pcie_set_mps(struct pci_dev *dev, int mps);
>  int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
>  			  enum pcie_link_width *width);
> +bool pcie_has_flr(struct pci_dev *dev);
>  void pcie_flr(struct pci_dev *dev);
>  int __pci_reset_function(struct pci_dev *dev);
>  int __pci_reset_function_locked(struct pci_dev *dev);
> -- 
> 2.9.5
>