Re: [PATCH 2/2] pci: Don't set RCB bit in LNKCTL if the upstream bridge hasn't

[Bjorn Helgaas]

On Mon, Nov 21, 2016 at 10:53:52AM -0600, Bjorn Helgaas wrote:
> On Wed, Nov 16, 2016 at 12:11:58PM -0600, Bjorn Helgaas wrote:
> > Hi Johannes,
> > 
> > On Wed, Nov 02, 2016 at 04:35:52PM -0600, Johannes Thumshirn wrote:
> > > The Read Completion Boundary (RCB) bit must only be set on a device or
> > > endpoint if it is set on the root complex.
> ...

> Here's the fixed one.

I applied the one below to for-linus for v4.9.

I did tweak the preceding patch to only share pcie_find_root_port()
inside drivers/pci -- moved the declaration from include/linux/pci.h
to drivers/pci/pci.h and moved the definition to drivers/pci/search.c.

I don't think it needs to be visible to the whole kernel.

> commit b7bff74c2e6babf12906291ee177f16444de81ad
> Author: Johannes Thumshirn <jthumshirn@xxxxxxx>
> Date:   Wed Nov 16 15:47:53 2016 -0600
> 
>     PCI: Set Read Completion Boundary to 128 iff Root Port supports it
>     
>     Per PCIe spec r3.0, sec 2.3.1.1, the Read Completion Boundary (RCB)
>     determines the naturally aligned address boundaries on which a Read Request
>     may be serviced with multiple Completions:
>     
>       - For a Root Complex, RCB is 64 bytes or 128 bytes
>         This value is reported in the Link Control Register
>     
>         Note: Bridges and Endpoints may implement a corresponding command bit
>         which may be set by system software to indicate the RCB value for the
>         Root Complex, allowing the Bridge/Endpoint to optimize its behavior
>         when the Root Complexâs RCB is 128 bytes.
>     
>       - For all other system elements, RCB is 128 bytes
>     
>     Per sec 7.8.7, if a Root Port only supports a 64-byte RCB, the RCB of all
>     downstream devices must be clear, indicating an RCB of 64 bytes.  If the
>     Root Port supports a 128-byte RCB, we may optionally set the RCB of
>     downstream devices so they know they can generate larger Completions.
>     
>     Some BIOSes supply an _HPX that tells us to set RCB, even though the Root
>     Port doesn't have RCB set, which may lead to Malformed TLP errors if the
>     Endpoint generates completions larger than the Root Port can handle.
>     
>     The IBM x3850 X6 with BIOS version -[A8E120CUS-1.30]- 08/22/2016 supplies
>     such an _HPX and a Mellanox MT27500 ConnectX-3 device fails to initialize:
>     
>       mlx4_core 0000:41:00.0: command 0xfff timed out (go bit not cleared)
>       mlx4_core 0000:41:00.0: device is going to be reset
>       mlx4_core 0000:41:00.0: Failed to obtain HW semaphore, aborting
>       mlx4_core 0000:41:00.0: Fail to reset HCA
>       ------------[ cut here ]------------
>       kernel BUG at drivers/net/ethernet/mellanox/mlx4/catas.c:193!
>     
>     After 6cd33649fa83 ("PCI: Add pci_configure_device() during enumeration")
>     and 7a1562d4f2d0 ("PCI: Apply _HPX Link Control settings to all devices
>     with a link"), we apply _HPX settings to *all* devices, not just those
>     hot-added after boot.
>     
>     Before 7a1562d4f2d0, we didn't touch the Mellanox RCB, and the device
>     worked.  After 7a1562d4f2d0, we set its RCB to 128, and it failed.
>     
>     Set the RCB to 128 iff the Root Port supports a 128-byte RCB.  Otherwise,
>     set RCB to 64 bytes.  This effectively ignores what _HPX tells us about
>     RCB.
>     
>     [bhelgaas: changelog, clear RCB if not set for Root Port]
>     Fixes: 6cd33649fa83 ("PCI: Add pci_configure_device() during enumeration")
>     Fixes: 7a1562d4f2d0 ("PCI: Apply _HPX Link Control settings to all devices with a link")
>     Link: https://bugzilla.kernel.org/show_bug.cgi?id=187781
>     Signed-off-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>     CC: stable@xxxxxxxxxxxxxxx	# v3.18+
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ab00267..104c46d 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1439,6 +1439,21 @@ static void program_hpp_type1(struct pci_dev *dev, struct hpp_type1 *hpp)
>  		dev_warn(&dev->dev, "PCI-X settings not supported\n");
>  }
>  
> +static bool pcie_root_rcb_set(struct pci_dev *dev)
> +{
> +	struct pci_dev *rp = pcie_find_root_port(dev);
> +	u16 lnkctl;
> +
> +	if (!rp)
> +		return false;
> +
> +	pcie_capability_read_word(rp, PCI_EXP_LNKCTL, &lnkctl);
> +	if (lnkctl & PCI_EXP_LNKCTL_RCB)
> +		return true;
> +
> +	return false;
> +}
> +
>  static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)
>  {
>  	int pos;
> @@ -1468,9 +1483,20 @@ static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)
>  			~hpp->pci_exp_devctl_and, hpp->pci_exp_devctl_or);
>  
>  	/* Initialize Link Control Register */
> -	if (pcie_cap_has_lnkctl(dev))
> +	if (pcie_cap_has_lnkctl(dev)) {
> +
> +		/*
> +		 * If the Root Port supports Read Completion Boundary of
> +		 * 128, set RCB to 128.  Otherwise, clear it.
> +		 */
> +		hpp->pci_exp_lnkctl_and |= PCI_EXP_LNKCTL_RCB;
> +		hpp->pci_exp_lnkctl_or &= ~PCI_EXP_LNKCTL_RCB;
> +		if (pcie_root_rcb_set(dev))
> +			hpp->pci_exp_lnkctl_or |= PCI_EXP_LNKCTL_RCB;
> +
>  		pcie_capability_clear_and_set_word(dev, PCI_EXP_LNKCTL,
>  			~hpp->pci_exp_lnkctl_and, hpp->pci_exp_lnkctl_or);
> +	}
>  
>  	/* Find Advanced Error Reporting Enhanced Capability */
>  	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ERR);
> --
> To unsubscribe from this list: send the line "unsubscribe linux-pci" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html