linux-kernel - Re: [PATCH 2/5] PCI: handle FLR failure and allow other reset types

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Message-ID: <20171011210057.GU25517@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 11 Oct 2017 16:00:58 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sinan Kaya <okaya@...eaurora.org>
Cc:     linux-pci@...r.kernel.org, timur@...eaurora.org,
        alex.williamson@...hat.com, linux-arm-msm@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/5] PCI: handle FLR failure and allow other reset types

On Sat, Sep 23, 2017 at 08:16:55PM -0400, Sinan Kaya wrote:
> pci_flr_wait() and pci_af_flr() functions assume graceful return even
> though the device is inaccessible under error conditions.
> 
> Return -ENOTTY in error cases so that __pci_reset_function_locked() can
> try other reset types if AF_FLR/FLR reset fails.

This makes sense to me, but I think the error handling in
__pci_reset_function_locked() is confusing.  It currently is:

  rc = pci_dev_specific_reset(dev, 0);
  if (rc != -ENOTTY)
    return rc;
  if (pcie_has_flr(dev)) {
    pcie_flr(dev);
    return 0;
  }
  rc = pci_af_flr(dev, 0);
  if (rc != -ENOTTY)
    return rc;

Would it make sense to change this to the following?

  rc = pci_dev_specific_reset(dev, 0);
  if (rc == 0)
    return 0;

  if (pcie_has_flr(dev)) {
    pcie_flr(dev);
    return 0;
  }

  rc = pci_af_flr(dev, 0);
  if (rc == 0)
    return 0;

I found two cases where this would make a difference: reset_ivb_igd()
returns -ENOMEM if pci_iomap() fails, and pci_pm_reset() returns
-EINVAL if the device is not in D0.

In both cases we currently return the failure, but it would seem
reasonable to me to try another reset method.

That could be done in a new patch before this one.  Then *this* patch
could use -ETIMEDOUT instead of -ENOTTY, and I think the whole thing
would become a little more readable.

> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
> ---
>  drivers/pci/pci.c   | 18 ++++++++++--------
>  include/linux/pci.h |  2 +-
>  2 files changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 23681f4..27ec45d 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3820,7 +3820,7 @@ int pci_wait_for_pending_transaction(struct pci_dev *dev)
>  }
>  EXPORT_SYMBOL(pci_wait_for_pending_transaction);
>  
> -static void pci_flr_wait(struct pci_dev *dev)
> +static int pci_flr_wait(struct pci_dev *dev)
>  {
>  	int delay = 1, timeout = 60000;
>  	u32 id;
> @@ -3849,7 +3849,7 @@ static void pci_flr_wait(struct pci_dev *dev)
>  		if (delay > timeout) {
>  			dev_warn(&dev->dev, "not ready %dms after FLR; giving up\n",
>  				 100 + delay - 1);
> -			return;
> +			return -ENOTTY;
>  		}
>  
>  		if (delay > 1000)
> @@ -3863,6 +3863,8 @@ static void pci_flr_wait(struct pci_dev *dev)
>  
>  	if (delay > 1000)
>  		dev_info(&dev->dev, "ready %dms after FLR\n", 100 + delay - 1);
> +
> +	return 0;
>  }
>  
>  /**
> @@ -3891,13 +3893,13 @@ static bool pcie_has_flr(struct pci_dev *dev)
>   * device supports FLR before calling this function, e.g. by using the
>   * pcie_has_flr() helper.
>   */
> -void pcie_flr(struct pci_dev *dev)
> +int pcie_flr(struct pci_dev *dev)
>  {
>  	if (!pci_wait_for_pending_transaction(dev))
>  		dev_err(&dev->dev, "timed out waiting for pending transaction; performing function level reset anyway\n");
>  
>  	pcie_capability_set_word(dev, PCI_EXP_DEVCTL, PCI_EXP_DEVCTL_BCR_FLR);
> -	pci_flr_wait(dev);
> +	return pci_flr_wait(dev);
>  }
>  EXPORT_SYMBOL_GPL(pcie_flr);
>  
> @@ -3930,8 +3932,7 @@ static int pci_af_flr(struct pci_dev *dev, int probe)
>  		dev_err(&dev->dev, "timed out waiting for pending transaction; performing AF function level reset anyway\n");
>  
>  	pci_write_config_byte(dev, pos + PCI_AF_CTRL, PCI_AF_CTRL_FLR);
> -	pci_flr_wait(dev);
> -	return 0;
> +	return pci_flr_wait(dev);
>  }
>  
>  /**
> @@ -4203,8 +4204,9 @@ int __pci_reset_function_locked(struct pci_dev *dev)
>  	if (rc != -ENOTTY)
>  		return rc;
>  	if (pcie_has_flr(dev)) {
> -		pcie_flr(dev);
> -		return 0;
> +		rc = pcie_flr(dev);
> +		if (rc != -ENOTTY)
> +			return rc;
>  	}
>  	rc = pci_af_flr(dev, 0);
>  	if (rc != -ENOTTY)
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index f68c58a..104224f7 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1088,7 +1088,7 @@ static inline int pci_is_managed(struct pci_dev *pdev)
>  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);
> -void pcie_flr(struct pci_dev *dev);
> +int pcie_flr(struct pci_dev *dev);
>  int __pci_reset_function(struct pci_dev *dev);
>  int __pci_reset_function_locked(struct pci_dev *dev);
>  int pci_reset_function(struct pci_dev *dev);
> -- 
> 1.9.1
> 
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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