RE: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed and whether it's limited

[Keller, Jacob E]

> -----Original Message-----
> From: Bjorn Helgaas [mailto:helgaas@xxxxxxxxxx]
> Sent: Friday, March 30, 2018 2:05 PM
> To: Tal Gilboa <talgi@xxxxxxxxxxxx>
> Cc: Tariq Toukan <tariqt@xxxxxxxxxxxx>; Keller, Jacob E
> <jacob.e.keller@xxxxxxxxx>; Ariel Elior <ariel.elior@xxxxxxxxxx>; Ganesh
> Goudar <ganeshgr@xxxxxxxxxxx>; Kirsher, Jeffrey T
> <jeffrey.t.kirsher@xxxxxxxxx>; everest-linux-l2@xxxxxxxxxx; intel-wired-
> lan@xxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-pci@xxxxxxxxxxxxxxx
> Subject: [PATCH v5 05/14] PCI: Add pcie_print_link_status() to log link speed and
> whether it's limited
> 
> From: Tal Gilboa <talgi@xxxxxxxxxxxx>
> 
> Add pcie_print_link_status().  This logs the current settings of the link
> (speed, width, and total available bandwidth).
> 
> If the device is capable of more bandwidth but is limited by a slower
> upstream link, we include information about the link that limits the
> device's performance.
> 
> The user may be able to move the device to a different slot for better
> performance.
> 
> This provides a unified method for all PCI devices to report status and
> issues, instead of each device reporting in a different way, using
> different code.
> 
> Signed-off-by: Tal Gilboa <talgi@xxxxxxxxxxxx>
> [bhelgaas: changelog, reword log messages, print device capabilities when
> not limited]
> Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> ---
>  drivers/pci/pci.c   |   29 +++++++++++++++++++++++++++++
>  include/linux/pci.h |    1 +
>  2 files changed, 30 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e00d56b12747..cec7aed09f6b 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5283,6 +5283,35 @@ u32 pcie_bandwidth_capable(struct pci_dev *dev,
> enum pci_bus_speed *speed,
>  	return *width * PCIE_SPEED2MBS_ENC(*speed);
>  }
> 
> +/**
> + * pcie_print_link_status - Report the PCI device's link speed and width
> + * @dev: PCI device to query
> + *
> + * Report the available bandwidth at the device.  If this is less than the
> + * device is capable of, report the device's maximum possible bandwidth and
> + * the upstream link that limits its performance to less than that.
> + */
> +void pcie_print_link_status(struct pci_dev *dev)
> +{
> +	enum pcie_link_width width, width_cap;
> +	enum pci_bus_speed speed, speed_cap;
> +	struct pci_dev *limiting_dev = NULL;
> +	u32 bw_avail, bw_cap;
> +
> +	bw_cap = pcie_bandwidth_capable(dev, &speed_cap, &width_cap);
> +	bw_avail = pcie_bandwidth_available(dev, &limiting_dev, &speed,
> &width);
> +
> +	if (bw_avail >= bw_cap)
> +		pci_info(dev, "%d Mb/s available bandwidth (%s x%d link)\n",
> +			 bw_cap, PCIE_SPEED2STR(speed_cap), width_cap);
> +	else
> +		pci_info(dev, "%d Mb/s available bandwidth, limited by %s x%d
> link at %s (capable of %d Mb/s with %s x%d link)\n",
> +			 bw_avail, PCIE_SPEED2STR(speed), width,
> +			 limiting_dev ? pci_name(limiting_dev) : "<unknown>",
> +			 bw_cap, PCIE_SPEED2STR(speed_cap), width_cap);
> +}

Personally, I would make thic last one a pci_warn() to indicate it at a higher log level, but I'm  ok with the wording, and if consensus is that this should be at info, I'm ok with that.

Thanks,
Jake

> +EXPORT_SYMBOL(pcie_print_link_status);
> +
>  /**
>   * pci_select_bars - Make BAR mask from the type of resource
>   * @dev: the PCI device for which BAR mask is made
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index f2bf2b7a66c7..38f7957121ef 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1086,6 +1086,7 @@ int pcie_get_minimum_link(struct pci_dev *dev, enum
> pci_bus_speed *speed,
>  u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev
> **limiting_dev,
>  			     enum pci_bus_speed *speed,
>  			     enum pcie_link_width *width);
> +void pcie_print_link_status(struct pci_dev *dev);
>  void pcie_flr(struct pci_dev *dev);
>  int __pci_reset_function_locked(struct pci_dev *dev);
>  int pci_reset_function(struct pci_dev *dev);