On Tue, 28 Jan 2025, Sasha Levin wrote: > From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> > > [ Upstream commit e5321ae10e1323359a5067a26dfe98b5f44cc5e6 ] > > eetlp_prefix_path in the struct pci_dev tells if End-End TLP Prefixes > are supported by the path or not, and 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 r6.2 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 r6.2 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. > > The value stored into eetlp_prefix_max is directly derived from device's > Max End-End TLP Prefixes and does not consider limitations imposed by > bridges or the Root Port beyond supported/not supported flags. This is > intentional for two reasons: > > 1) PCIe r6.2 spec sections 2.2.10.4 & 6.2.4.4 indicate that a TLP is > malformed only if the number of prefixes exceed the number of Max > End-End TLP Prefixes, which seems to be the case even if the device > could never receive that many prefixes due to smaller maximum imposed > by a bridge or the Root Port. If TLP parsing is later added, this > distinction is significant in interpreting what is logged by the TLP > Prefix Log registers and the value matching to the Malformed TLP > threshold is going to be more useful. > > 2) TLP Prefix handling happens autonomously on a low layer and the value > in eetlp_prefix_max is not programmed anywhere by the kernel (i.e., > there is no limiter OS can control to prevent sending more than N TLP > Prefixes). > > Link: https://lore.kernel.org/r/20250114170840.1633-7-ilpo.jarvinen@xxxxxxxxxxxxxxx > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx> > Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> > Reviewed-by: Yazen Ghannam <yazen.ghannam@xxxxxxx> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> Hi, Why is this being auto selected? It's not a fix nor do I see any dependency related tags. Unless the entire TLP consolidation would be going into stable, I don't see much value for this change in stable kernels. -- i. > --- > 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 6afff1f1b1430..c6b266c772c81 100644 > --- a/drivers/pci/ats.c > +++ b/drivers/pci/ats.c > @@ -410,7 +410,7 @@ 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 2e81ab0f5a25c..381c22e3ccdbf 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -2251,8 +2251,8 @@ 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; > > @@ -2264,15 +2264,19 @@ 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) > + dev->eetlp_prefix_max = eetlp_max; > } > -#endif > } > > static void pci_configure_serr(struct pci_dev *dev) > diff --git a/include/linux/pci.h b/include/linux/pci.h > index db9b47ce3eefd..21be5a1edf1ad 100644 > --- a/include/linux/pci.h > +++ b/include/linux/pci.h > @@ -407,7 +407,7 @@ struct pci_dev { > supported from root to here */ > #endif > unsigned int pasid_no_tlp:1; /* PASID works without TLP Prefix */ > - unsigned int eetlp_prefix_path:1; /* End-to-End TLP Prefix */ > + unsigned int eetlp_prefix_max:3; /* Max # of End-End TLP Prefixes, 0=not supported */ > > pci_channel_state_t error_state; /* Current connectivity state */ > struct device dev; /* Generic device interface */ > diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h > index 1601c7ed5fab7..14a6306c4ce18 100644 > --- a/include/uapi/linux/pci_regs.h > +++ b/include/uapi/linux/pci_regs.h > @@ -665,6 +665,7 @@ > #define PCI_EXP_DEVCAP2_OBFF_MSG 0x00040000 /* New message signaling */ > #define PCI_EXP_DEVCAP2_OBFF_WAKE 0x00080000 /* Re-use WAKE# for OBFF */ > #define PCI_EXP_DEVCAP2_EE_PREFIX 0x00200000 /* End-End TLP Prefix */ > +#define PCI_EXP_DEVCAP2_EE_PREFIX_MAX 0x00c00000 /* Max End-End TLP Prefixes */ > #define PCI_EXP_DEVCTL2 0x28 /* Device Control 2 */ > #define PCI_EXP_DEVCTL2_COMP_TIMEOUT 0x000f /* Completion Timeout Value */ > #define PCI_EXP_DEVCTL2_COMP_TMOUT_DIS 0x0010 /* Completion Timeout Disable */ >
