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Message-ID: <19475994-b606-604e-f17d-a5251026c4df@linux.intel.com>
Date: Tue, 28 Jan 2025 20:00:39 +0200 (EET)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Sasha Levin <sashal@...nel.org>
cc: LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
Bjorn Helgaas <bhelgaas@...gle.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Yazen Ghannam <yazen.ghannam@....com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.13 13/15] PCI: Store number of supported End-End
TLP Prefixes
On Tue, 28 Jan 2025, Sasha Levin wrote:
> From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>
> [ 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@linux.intel.com
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: Yazen Ghannam <yazen.ghannam@....com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
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 */
>
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