Re: [PATCH v6 5/8] PCI: Store # of supported End-End TLP Prefixes

Jonathan Cameron
2024-12-11T16:36:34Z

On Fri, 13 Sep 2024 17:36:29 +0300
Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> wrote:

> eetlp_prefix_path in the struct pci_dev tells if End-End TLP Prefixes
> are supported by the path or not, the value is only calculated if
> CONFIG_PCI_PASID is set.
>
> The Max End-End TLP Prefixes field in the Device Capabilities Register
> 2 also tells how many (1-4) End-End TLP Prefixes are supported (PCIe r6
> sec 7.5.3.15). The number of supported End-End Prefixes is useful for
> reading correct number of DWORDs from TLP Prefix Log register in AER
> capability (PCIe r6 sec 7.8.4.12).
>
> Replace eetlp_prefix_path with eetlp_prefix_max and determine the
> number of supported End-End Prefixes regardless of CONFIG_PCI_PASID so
> that an upcoming commit generalizing TLP Prefix Log register reading
> does not have to read extra DWORDs for End-End Prefixes that never will
> be there.
>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> ---
> drivers/pci/ats.c | 2 +-
> drivers/pci/probe.c | 14 +++++++++-----
> include/linux/pci.h | 2 +-
> include/uapi/linux/pci_regs.h | 1 +
> 4 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index c570892b2090..e13433dcfc82 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -377,7 +377,7 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
> if (WARN_ON(pdev->pasid_enabled))
> return -EBUSY;
>
> - if (!pdev->eetlp_prefix_path && !pdev->pasid_no_tlp)
> + if (!pdev->eetlp_prefix_max && !pdev->pasid_no_tlp)
> return -EINVAL;
>
> if (!pasid)
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index b14b9876c030..0ab70ea6840c 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2228,8 +2228,8 @@ static void pci_configure_relaxed_ordering(struct pci_dev *dev)
>
> static void pci_configure_eetlp_prefix(struct pci_dev *dev)
> {
> -#ifdef CONFIG_PCI_PASID
> struct pci_dev *bridge;
> + unsigned int eetlp_max;
> int pcie_type;
> u32 cap;
>
> @@ -2241,15 +2241,19 @@ static void pci_configure_eetlp_prefix(struct pci_dev *dev)
> return;
>
> pcie_type = pci_pcie_type(dev);
> +
> + eetlp_max = FIELD_GET(PCI_EXP_DEVCAP2_EE_PREFIX_MAX, cap);
> + /* 00b means 4 */
> + eetlp_max = eetlp_max ?: 4;
> +
> if (pcie_type == PCI_EXP_TYPE_ROOT_PORT ||
> pcie_type == PCI_EXP_TYPE_RC_END)
> - dev->eetlp_prefix_path = 1;
> + dev->eetlp_prefix_max = eetlp_max;
> else {
> bridge = pci_upstream_bridge(dev);
> - if (bridge && bridge->eetlp_prefix_path)
> - dev->eetlp_prefix_path = 1;
> + if (bridge && bridge->eetlp_prefix_max)

What happens if they disagree? That is the bridge supports 2
and the device 3?

> + dev->eetlp_prefix_max = eetlp_max;
> }
> -#endif
> }

>