[v6,5/5] PCI: Remove unused pcie_get_minimum_link()

Message ID 152537764322.62474.552711932384023140.stgit@bhelgaas-glaptop.roam.corp.google.com
State Accepted
Delegated to: Bjorn Helgaas
Headers show
Series
  • PCI: Improve PCIe link status reporting
Related show

Commit Message

Bjorn Helgaas May 3, 2018, 8 p.m.
From: Bjorn Helgaas <bhelgaas@google.com>

In some cases pcie_get_minimum_link() returned misleading information
because it found the slowest link and the narrowest link without
considering the total bandwidth of the link.

For example, consider a path with these two links:

  - 16.0 GT/s  x1 link  (16.0 * 10^9 * 128 / 130) *  1 / 8 = 1969 MB/s
  -  2.5 GT/s x16 link  ( 2.5 * 10^9 *   8 /  10) * 16 / 8 = 4000 MB/s

The available bandwidth of the path is limited by the 16 GT/s link to about
1969 MB/s, but pcie_get_minimum_link() returned 2.5 GT/s x1, which
corresponds to only 250 MB/s.

Callers should use pcie_print_link_status() instead, or
pcie_bandwidth_available() if they need more detailed information.

Remove pcie_get_minimum_link() since there are no callers left.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 drivers/pci/pci.c   |   43 -------------------------------------------
 include/linux/pci.h |    2 --
 2 files changed, 45 deletions(-)

Comments

Bjorn Helgaas May 10, 2018, 4:33 p.m. | #1
On Thu, May 03, 2018 at 03:00:43PM -0500, Bjorn Helgaas wrote:
> From: Bjorn Helgaas <bhelgaas@google.com>
> 
> In some cases pcie_get_minimum_link() returned misleading information
> because it found the slowest link and the narrowest link without
> considering the total bandwidth of the link.
> 
> For example, consider a path with these two links:
> 
>   - 16.0 GT/s  x1 link  (16.0 * 10^9 * 128 / 130) *  1 / 8 = 1969 MB/s
>   -  2.5 GT/s x16 link  ( 2.5 * 10^9 *   8 /  10) * 16 / 8 = 4000 MB/s
> 
> The available bandwidth of the path is limited by the 16 GT/s link to about
> 1969 MB/s, but pcie_get_minimum_link() returned 2.5 GT/s x1, which
> corresponds to only 250 MB/s.
> 
> Callers should use pcie_print_link_status() instead, or
> pcie_bandwidth_available() if they need more detailed information.
> 
> Remove pcie_get_minimum_link() since there are no callers left.
> 
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Hi Jeff,

I got your note that you applied this to dev-queue.  I assume that
means you also applied the preceding patches that removed all the
users.  I got a note about ixgbe, but not the others, so I'm just
double-checking.

> ---
>  drivers/pci/pci.c   |   43 -------------------------------------------
>  include/linux/pci.h |    2 --
>  2 files changed, 45 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e597655a5643..4bafa817c40a 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5069,49 +5069,6 @@ int pcie_set_mps(struct pci_dev *dev, int mps)
>  }
>  EXPORT_SYMBOL(pcie_set_mps);
>  
> -/**
> - * pcie_get_minimum_link - determine minimum link settings of a PCI device
> - * @dev: PCI device to query
> - * @speed: storage for minimum speed
> - * @width: storage for minimum width
> - *
> - * This function will walk up the PCI device chain and determine the minimum
> - * link width and speed of the device.
> - */
> -int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
> -			  enum pcie_link_width *width)
> -{
> -	int ret;
> -
> -	*speed = PCI_SPEED_UNKNOWN;
> -	*width = PCIE_LNK_WIDTH_UNKNOWN;
> -
> -	while (dev) {
> -		u16 lnksta;
> -		enum pci_bus_speed next_speed;
> -		enum pcie_link_width next_width;
> -
> -		ret = pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
> -		if (ret)
> -			return ret;
> -
> -		next_speed = pcie_link_speed[lnksta & PCI_EXP_LNKSTA_CLS];
> -		next_width = (lnksta & PCI_EXP_LNKSTA_NLW) >>
> -			PCI_EXP_LNKSTA_NLW_SHIFT;
> -
> -		if (next_speed < *speed)
> -			*speed = next_speed;
> -
> -		if (next_width < *width)
> -			*width = next_width;
> -
> -		dev = dev->bus->self;
> -	}
> -
> -	return 0;
> -}
> -EXPORT_SYMBOL(pcie_get_minimum_link);
> -
>  /**
>   * pcie_bandwidth_available - determine minimum link settings of a PCIe
>   *			      device and its bandwidth limitation
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 73178a2fcee0..230615620a4a 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1079,8 +1079,6 @@ int pcie_get_readrq(struct pci_dev *dev);
>  int pcie_set_readrq(struct pci_dev *dev, int rq);
>  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);
>  u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev **limiting_dev,
>  			     enum pci_bus_speed *speed,
>  			     enum pcie_link_width *width);
>
Jeff Kirsher May 10, 2018, 8:34 p.m. | #2
On Thu, 2018-05-10 at 11:33 -0500, Bjorn Helgaas wrote:
> On Thu, May 03, 2018 at 03:00:43PM -0500, Bjorn Helgaas wrote:
> > From: Bjorn Helgaas <bhelgaas@google.com>
> > 
> > In some cases pcie_get_minimum_link() returned misleading
> > information
> > because it found the slowest link and the narrowest link without
> > considering the total bandwidth of the link.
> > 
> > For example, consider a path with these two links:
> > 
> >    - 16.0 GT/s  x1 link  (16.0 * 10^9 * 128 / 130) *  1 / 8 = 1969
> > MB/s
> >    -  2.5 GT/s x16 link  ( 2.5 * 10^9 *   8 /  10) * 16 / 8 = 4000
> > MB/s
> > 
> > The available bandwidth of the path is limited by the 16 GT/s link
> > to about
> > 1969 MB/s, but pcie_get_minimum_link() returned 2.5 GT/s x1, which
> > corresponds to only 250 MB/s.
> > 
> > Callers should use pcie_print_link_status() instead, or
> > pcie_bandwidth_available() if they need more detailed information.
> > 
> > Remove pcie_get_minimum_link() since there are no callers left.
> > 
> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> 
> Hi Jeff,
> 
> I got your note that you applied this to dev-queue.  I assume that
> means you also applied the preceding patches that removed all the
> users.  I got a note about ixgbe, but not the others, so I'm just
> double-checking.

I did initially apply it, but realized that I would have to apply the
earlier patches as well, which did not pertain to the Intel wired LAN
drivers.  So I have removed this patch from queue and will only be
testing the ixgbe patch of the series, which Andrew has already tested
and responded to.

Patch

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e597655a5643..4bafa817c40a 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5069,49 +5069,6 @@  int pcie_set_mps(struct pci_dev *dev, int mps)
 }
 EXPORT_SYMBOL(pcie_set_mps);
 
-/**
- * pcie_get_minimum_link - determine minimum link settings of a PCI device
- * @dev: PCI device to query
- * @speed: storage for minimum speed
- * @width: storage for minimum width
- *
- * This function will walk up the PCI device chain and determine the minimum
- * link width and speed of the device.
- */
-int pcie_get_minimum_link(struct pci_dev *dev, enum pci_bus_speed *speed,
-			  enum pcie_link_width *width)
-{
-	int ret;
-
-	*speed = PCI_SPEED_UNKNOWN;
-	*width = PCIE_LNK_WIDTH_UNKNOWN;
-
-	while (dev) {
-		u16 lnksta;
-		enum pci_bus_speed next_speed;
-		enum pcie_link_width next_width;
-
-		ret = pcie_capability_read_word(dev, PCI_EXP_LNKSTA, &lnksta);
-		if (ret)
-			return ret;
-
-		next_speed = pcie_link_speed[lnksta & PCI_EXP_LNKSTA_CLS];
-		next_width = (lnksta & PCI_EXP_LNKSTA_NLW) >>
-			PCI_EXP_LNKSTA_NLW_SHIFT;
-
-		if (next_speed < *speed)
-			*speed = next_speed;
-
-		if (next_width < *width)
-			*width = next_width;
-
-		dev = dev->bus->self;
-	}
-
-	return 0;
-}
-EXPORT_SYMBOL(pcie_get_minimum_link);
-
 /**
  * pcie_bandwidth_available - determine minimum link settings of a PCIe
  *			      device and its bandwidth limitation
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 73178a2fcee0..230615620a4a 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -1079,8 +1079,6 @@  int pcie_get_readrq(struct pci_dev *dev);
 int pcie_set_readrq(struct pci_dev *dev, int rq);
 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);
 u32 pcie_bandwidth_available(struct pci_dev *dev, struct pci_dev **limiting_dev,
 			     enum pci_bus_speed *speed,
 			     enum pcie_link_width *width);