Re: [PATCH v8 2/8] PCI: Add new array for keeping track of ordering of reset methods

[Alex Williamson]

On Tue, 29 Jun 2021 21:30:58 +0530
Amey Narkhede <ameynarkhede03@xxxxxxxxx> wrote:

> Introduce a new array reset_methods in struct pci_dev to keep track of
> reset mechanisms supported by the device and their ordering.
> 
> Also refactor probing and reset functions to take advantage of calling
> convention of reset functions.
> 
> Co-developed-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> Signed-off-by: Amey Narkhede <ameynarkhede03@xxxxxxxxx>
> ---
>  drivers/pci/pci.c   | 97 ++++++++++++++++++++++++++-------------------
>  drivers/pci/pci.h   |  9 ++++-
>  drivers/pci/probe.c |  5 +--
>  include/linux/pci.h |  7 ++++
>  4 files changed, 74 insertions(+), 44 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 28f099a4f..1932c7ec4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -72,6 +72,14 @@ static void pci_dev_d3_sleep(struct pci_dev *dev)
>  		msleep(delay);
>  }
>  
> +int pci_reset_supported(struct pci_dev *dev)
> +{
> +	u8 null_reset_methods[PCI_NUM_RESET_METHODS] = { 0 };
> +
> +	return memcmp(null_reset_methods,
> +		      dev->reset_methods, sizeof(null_reset_methods));
> +}
> +
>  #ifdef CONFIG_PCI_DOMAINS
>  int pci_domains_supported = 1;
>  #endif
> @@ -5101,6 +5109,19 @@ static void pci_dev_restore(struct pci_dev *dev)
>  		err_handler->reset_done(dev);
>  }
>  
> +/*
> + * The ordering for functions in pci_reset_fn_methods is required for
> + * reset_methods byte array defined in struct pci_dev.
> + */

Is this comment still relevant?  Ordering here defines the default
priority scheme, but now that index=priority rather than index=method
in reset_methods, I'm not sure these comments are very clear.  Thanks,

Alex

> +const struct pci_reset_fn_method pci_reset_fn_methods[] = {
> +	{ },
> +	{ &pci_dev_specific_reset, .name = "device_specific" },
> +	{ &pcie_reset_flr, .name = "flr" },
> +	{ &pci_af_flr, .name = "af_flr" },
> +	{ &pci_pm_reset, .name = "pm" },
> +	{ &pci_reset_bus_function, .name = "bus" },
> +};
> +
>  /**
>   * __pci_reset_function_locked - reset a PCI device function while holding
>   * the @dev mutex lock.
> @@ -5123,65 +5144,61 @@ static void pci_dev_restore(struct pci_dev *dev)
>   */
>  int __pci_reset_function_locked(struct pci_dev *dev)
>  {
> -	int rc;
> +	int i, m, rc = -ENOTTY;
>  
>  	might_sleep();
>  
>  	/*
> -	 * A reset method returns -ENOTTY if it doesn't support this device
> -	 * and we should try the next method.
> +	 * A reset method returns -ENOTTY if it doesn't support this device and
> +	 * we should try the next method.
>  	 *
> -	 * If it returns 0 (success), we're finished.  If it returns any
> -	 * other error, we're also finished: this indicates that further
> -	 * reset mechanisms might be broken on the device.
> +	 * If it returns 0 (success), we're finished.  If it returns any other
> +	 * error, we're also finished: this indicates that further reset
> +	 * mechanisms might be broken on the device.
>  	 */
> -	rc = pci_dev_specific_reset(dev, 0);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	rc = pcie_reset_flr(dev, 0);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	rc = pci_af_flr(dev, 0);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	rc = pci_pm_reset(dev, 0);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	return pci_reset_bus_function(dev, 0);
> +	for (i = 0; i <  PCI_NUM_RESET_METHODS && (m = dev->reset_methods[i]); i++) {
> +		rc = pci_reset_fn_methods[m].reset_fn(dev, 0);
> +		if (!rc)
> +			return 0;
> +		if (rc != -ENOTTY)
> +			return rc;
> +	}
> +
> +	return -ENOTTY;
>  }
>  EXPORT_SYMBOL_GPL(__pci_reset_function_locked);
>  
>  /**
> - * pci_probe_reset_function - check whether the device can be safely reset
> - * @dev: PCI device to reset
> + * pci_init_reset_methods - check whether device can be safely reset
> + * and store supported reset mechanisms.
> + * @dev: PCI device to check for reset mechanisms
>   *
>   * Some devices allow an individual function to be reset without affecting
>   * other functions in the same device.  The PCI device must be responsive
> - * to PCI config space in order to use this function.
> + * to reads and writes to its PCI config space in order to use this function.
>   *
> - * Returns 0 if the device function can be reset or negative if the
> - * device doesn't support resetting a single function.
> + * Stores reset mechanisms supported by device in reset_methods byte array
> + * which is a member of struct pci_dev.
>   */
> -int pci_probe_reset_function(struct pci_dev *dev)
> +void pci_init_reset_methods(struct pci_dev *dev)
>  {
> -	int rc;
> +	int i, n, rc;
> +	u8 reset_methods[PCI_NUM_RESET_METHODS] = { 0 };
>  
> -	might_sleep();
> +	n = 0;
>  
> -	rc = pci_dev_specific_reset(dev, 1);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	rc = pcie_reset_flr(dev, 1);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	rc = pci_af_flr(dev, 1);
> -	if (rc != -ENOTTY)
> -		return rc;
> -	rc = pci_pm_reset(dev, 1);
> -	if (rc != -ENOTTY)
> -		return rc;
> +	BUILD_BUG_ON(ARRAY_SIZE(pci_reset_fn_methods) != PCI_NUM_RESET_METHODS);
>  
> -	return pci_reset_bus_function(dev, 1);
> +	might_sleep();
> +
> +	for (i = 1; i < PCI_NUM_RESET_METHODS; i++) {
> +		rc = pci_reset_fn_methods[i].reset_fn(dev, 1);
> +		if (!rc)
> +			reset_methods[n++] = i;
> +		else if (rc != -ENOTTY)
> +			break;
> +	}
> +	memcpy(dev->reset_methods, reset_methods, sizeof(reset_methods));
>  }
>  
>  /**
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index 37c913bbc..db1ad94e7 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -33,7 +33,8 @@ enum pci_mmap_api {
>  int pci_mmap_fits(struct pci_dev *pdev, int resno, struct vm_area_struct *vmai,
>  		  enum pci_mmap_api mmap_api);
>  
> -int pci_probe_reset_function(struct pci_dev *dev);
> +int pci_reset_supported(struct pci_dev *dev);
> +void pci_init_reset_methods(struct pci_dev *dev);
>  int pci_bridge_secondary_bus_reset(struct pci_dev *dev);
>  int pci_bus_error_reset(struct pci_dev *dev);
>  
> @@ -606,6 +607,12 @@ struct pci_dev_reset_methods {
>  	int (*reset)(struct pci_dev *dev, int probe);
>  };
>  
> +struct pci_reset_fn_method {
> +	int (*reset_fn)(struct pci_dev *pdev, int probe);
> +	char *name;
> +};
> +
> +extern const struct pci_reset_fn_method pci_reset_fn_methods[];
>  #ifdef CONFIG_PCI_QUIRKS
>  int pci_dev_specific_reset(struct pci_dev *dev, int probe);
>  #else
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 862d91615..7355769f8 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2406,9 +2406,8 @@ static void pci_init_capabilities(struct pci_dev *dev)
>  	pci_rcec_init(dev);		/* Root Complex Event Collector */
>  
>  	pcie_report_downtraining(dev);
> -
> -	if (pci_probe_reset_function(dev) == 0)
> -		dev->reset_fn = 1;
> +	pci_init_reset_methods(dev);
> +	dev->reset_fn = pci_reset_supported(dev);
>  }
>  
>  /*
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 74f42a2cd..bce3d3e52 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -49,6 +49,9 @@
>  			       PCI_STATUS_SIG_TARGET_ABORT | \
>  			       PCI_STATUS_PARITY)
>  
> +/* Number of reset methods used in pci_reset_fn_methods array in pci.c */
> +#define PCI_NUM_RESET_METHODS 6
> +
>  /*
>   * The PCI interface treats multi-function devices as independent
>   * devices.  The slot/function address of each device is encoded
> @@ -504,6 +507,10 @@ struct pci_dev {
>  	char		*driver_override; /* Driver name to force a match */
>  
>  	unsigned long	priv_flags;	/* Private flags for the PCI driver */
> +	/*
> +	 * See pci_reset_fn_methods array in pci.c for ordering.
> +	 */
> +	u8 reset_methods[PCI_NUM_RESET_METHODS];	/* Reset methods ordered by priority */
>  };
>  
>  static inline struct pci_dev *pci_physfn(struct pci_dev *dev)