Re: [PATCH] PCI: Make pcie_find_root_port() work for PCIe root ports as well

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Jun 22, 2020 at 07:12:48PM +0300, Mika Westerberg wrote:
> Commit 6ae72bfa656e ("PCI: Unify pcie_find_root_port() and
> pci_find_pcie_root_port()") unified the root port finding functionality
> into a single function but missed the fact that the passed in device may
> already be a root port. This causes the kernel to block power management
> of PCIe hierarchies in recent systems because ->bridge_d3 started to
> return false for such ports after the commit in question.
> 
> Fixes: 6ae72bfa656e ("PCI: Unify pcie_find_root_port() and pci_find_pcie_root_port()")
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> Cc: stable@vger.kernel.org
> ---
>  include/linux/pci.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index c79d83304e52..c17c24f5eeed 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -2169,8 +2169,13 @@ static inline int pci_pcie_type(const struct pci_dev *dev)
>   */
>  static inline struct pci_dev *pcie_find_root_port(struct pci_dev *dev)
>  {
> -	struct pci_dev *bridge = pci_upstream_bridge(dev);
> +	struct pci_dev *bridge;
>  
> +	/* If dev is already root port */
> +	if (pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
> +		return dev;
> +
> +	bridge = pci_upstream_bridge(dev);
>  	while (bridge) {
>  		if (pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT)
>  			return bridge;

I applied the patch below, which is slightly simplified but I think
still equivalent, to for-linus for v5.8.  Let me know if it's not.

I dropped the stable tag because 6ae72bfa656e was merged for v5.8-rc1,
and I assume v5.7 works correctly so it doesn't need any change.


commit 5396956cc7c6 ("PCI: Make pcie_find_root_port() work for Root Ports")
Author: Mika Westerberg <mika.westerberg@linux.intel.com>
Date:   Mon Jun 22 19:12:48 2020 +0300

    PCI: Make pcie_find_root_port() work for Root Ports
    
    Commit 6ae72bfa656e ("PCI: Unify pcie_find_root_port() and
    pci_find_pcie_root_port()") broke acpi_pci_bridge_d3() because calling
    pcie_find_root_port() on a Root Port returned NULL when it should return
    the Root Port, which in turn broke power management of PCIe hierarchies.
    
    Rework pcie_find_root_port() so it returns its argument when it is already
    a Root Port.
    
    [bhelgaas: test device only once, test for PCIe]
    Fixes: 6ae72bfa656e ("PCI: Unify pcie_find_root_port() and pci_find_pcie_root_port()")
    Link: https://lore.kernel.org/r/20200622161248.51099-1-mika.westerberg@linux.intel.com
    Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

diff --git a/include/linux/pci.h b/include/linux/pci.h
index c79d83304e52..34c1c4f45288 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -2169,12 +2169,11 @@ static inline int pci_pcie_type(const struct pci_dev *dev)
  */
 static inline struct pci_dev *pcie_find_root_port(struct pci_dev *dev)
 {
-	struct pci_dev *bridge = pci_upstream_bridge(dev);
-
-	while (bridge) {
-		if (pci_pcie_type(bridge) == PCI_EXP_TYPE_ROOT_PORT)
-			return bridge;
-		bridge = pci_upstream_bridge(bridge);
+	while (dev) {
+		if (pci_is_pcie(dev) &&
+		    pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT)
+			return dev;
+		dev = pci_upstream_bridge(dev);
 	}
 
 	return NULL;