Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

Bjorn Helgaas
2020-10-30T19:52:36Z

On Fri, Oct 30, 2020 at 11:51:32AM -0700, Dave Jiang wrote:
> Intel Scalable I/O Virtualization (SIOV) enables sharing of I/O devices
> across isolated domains through PASID based sub-device partitioning.
> Interrupt Message Storage (IMS) enables devices to store the interrupt
> messages in a device-specific optimized manner without the scalability
> restrictions of the PCIe defined MSI-X capability. IMS is one of the
> features supported under SIOV.
>
> Move SIOV detection code from Intel iommu driver code to common PCI. Making
> the detection code common allows supported accelerator drivers to query the
> PCI core for SIOV and IMS capabilities. The support code will add the
> ability to query the PCI DVSEC capabilities for the SIOV cap.

This patch really does not include anything related to SIOV other than
adding a little code to *find* the capability. It doesn't add
anything that actually *uses* it. I think this patch should simply
add pci_find_dvsec(), and it doesn't need any of this SIOV or IMS
description.

> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Baolu Lu <baolu.lu@intel.com>
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> Reviewed-by: Ashok Raj <ashok.raj@intel.com>
> ---
> drivers/iommu/intel/iommu.c | 31 ++-----------------------
> drivers/pci/Kconfig | 15 ++++++++++++
> drivers/pci/Makefile | 2 ++
> drivers/pci/dvsec.c | 40 +++++++++++++++++++++++++++++++++
> drivers/pci/siov.c | 50 +++++++++++++++++++++++++++++++++++++++++
> include/linux/pci-siov.h | 18 +++++++++++++++
> include/linux/pci.h | 3 ++
> include/uapi/linux/pci_regs.h | 4 +++
> 8 files changed, 134 insertions(+), 29 deletions(-)
> create mode 100644 drivers/pci/dvsec.c
> create mode 100644 drivers/pci/siov.c
> create mode 100644 include/linux/pci-siov.h
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 3e77a88b236c..d9335f590b42 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -36,6 +36,7 @@
> #include <linux/tboot.h>
> #include <linux/dmi.h>
> #include <linux/pci-ats.h>
> +#include <linux/pci-siov.h>
> #include <linux/memblock.h>
> #include <linux/dma-map-ops.h>
> #include <linux/dma-direct.h>
> @@ -5883,34 +5884,6 @@ static int intel_iommu_disable_auxd(struct device *dev)
> return 0;
> }
>
> -/*
> - * A PCI express designated vendor specific extended capability is defined
> - * in the section 3.7 of Intel scalable I/O virtualization technical spec
> - * for system software and tools to detect endpoint devices supporting the
> - * Intel scalable IO virtualization without host driver dependency.
> - *
> - * Returns the address of the matching extended capability structure within
> - * the device's PCI configuration space or 0 if the device does not support
> - * it.
> - */
> -static int siov_find_pci_dvsec(struct pci_dev *pdev)
> -{
> - int pos;
> - u16 vendor, id;
> -
> - pos = pci_find_next_ext_capability(pdev, 0, 0x23);
> - while (pos) {
> - pci_read_config_word(pdev, pos + 4, &vendor);
> - pci_read_config_word(pdev, pos + 8, &id);
> - if (vendor == PCI_VENDOR_ID_INTEL && id == 5)
> - return pos;
> -
> - pos = pci_find_next_ext_capability(pdev, pos, 0x23);
> - }
> -
> - return 0;
> -}
> -
> static bool
> intel_iommu_dev_has_feat(struct device *dev, enum iommu_dev_features feat)
> {
> @@ -5925,7 +5898,7 @@ intel_iommu_dev_has_feat(struct device *dev, enum iommu_dev_features feat)
> if (ret < 0)
> return false;
>
> - return !!siov_find_pci_dvsec(to_pci_dev(dev));
> + return pci_siov_supported(to_pci_dev(dev));
> }
>
> if (feat == IOMMU_DEV_FEAT_SVA) {
> diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
> index 0c473d75e625..cf7f4d17d8cc 100644
> --- a/drivers/pci/Kconfig
> +++ b/drivers/pci/Kconfig
> @@ -161,6 +161,21 @@ config PCI_PASID
>
> If unsure, say N.
>
> +config PCI_DVSEC
> + bool
> +
> +config PCI_SIOV
> + select PCI_PASID

This patch has nothing to do with PCI_PASID. If you want to add this
select later in a patch that *does* add something that requires
PCI_PASID, that's OK.

> + select PCI_DVSEC
> + bool "PCI SIOV support"
> + help
> + Scalable I/O Virtualzation enables sharing of I/O devices across isolated
> + domains through PASID based sub-device partitioning. One of the sub features
> + supported by SIOV is Inetrrupt Message Storage (IMS). Select this option if
> + you want to compile the support into your kernel.
> + If unsure, say N.
> +
> config PCI_P2PDMA
> bool "PCI peer-to-peer transfer support"
> depends on ZONE_DEVICE
> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> index 522d2b974e91..653a1d69b0fc 100644
> --- a/drivers/pci/Makefile
> +++ b/drivers/pci/Makefile
> @@ -20,6 +20,8 @@ obj-$(CONFIG_PCI_QUIRKS) += quirks.o
> obj-$(CONFIG_HOTPLUG_PCI) += hotplug/
> obj-$(CONFIG_PCI_MSI) += msi.o
> obj-$(CONFIG_PCI_ATS) += ats.o
> +obj-$(CONFIG_PCI_DVSEC) += dvsec.o
> +obj-$(CONFIG_PCI_SIOV) += siov.o
> obj-$(CONFIG_PCI_IOV) += iov.o
> obj-$(CONFIG_PCI_BRIDGE_EMUL) += pci-bridge-emul.o
> obj-$(CONFIG_PCI_LABEL) += pci-label.o
> diff --git a/drivers/pci/dvsec.c b/drivers/pci/dvsec.c
> new file mode 100644
> index 000000000000..e49b079f0717
> --- /dev/null
> +++ b/drivers/pci/dvsec.c
> @@ -0,0 +1,40 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * PCI DVSEC helper functions
> + * Copyright (C) 2020 Intel Corp.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/pci.h>
> +#include <uapi/linux/pci_regs.h>
> +#include "pci.h"
> +
> +/**
> + * pci_find_dvsec - return position of DVSEC with provided vendor and dvsec id
> + * @dev: the PCI device
> + * @vendor: Vendor for the DVSEC
> + * @id: the DVSEC cap id
> + *
> + * Return the offset of DVSEC on success or -ENOTSUPP if not found

s/vendor/Vendor/
s/dvsec/DVSEC/
s/id/ID/ twice above

Please put this function in drivers/pci/pci.c next to
pci_find_ext_capability(). I don't think it's worth making a new file
just for this.

> + */
> +int pci_find_dvsec(struct pci_dev *dev, u16 vendor, u16 id)
> +{
> + u16 dev_vendor, dev_id;
> + int pos;
> +
> + pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_DVSEC);
> + if (!pos)
> + return -ENOTSUPP;
> +
> + while (pos) {
> + pci_read_config_word(dev, pos + PCI_DVSEC_HEADER1, &dev_vendor);
> + pci_read_config_word(dev, pos + PCI_DVSEC_HEADER2, &dev_id);
> + if (dev_vendor == vendor && dev_id == id)
> + return pos;
> +
> + pos = pci_find_next_ext_capability(dev, pos, PCI_EXT_CAP_ID_DVSEC);
> + }
> +
> + return -ENOTSUPP;
> +}
> +EXPORT_SYMBOL_GPL(pci_find_dvsec);
> diff --git a/drivers/pci/siov.c b/drivers/pci/siov.c
> new file mode 100644
> index 000000000000..6147e6ae5832
> --- /dev/null
> +++ b/drivers/pci/siov.c
> @@ -0,0 +1,50 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Intel Scalable I/O Virtualization support
> + * Copyright (C) 2020 Intel Corp.
> + */
> +
> +#include <linux/export.h>
> +#include <linux/pci.h>
> +#include <linux/pci-siov.h>
> +#include <uapi/linux/pci_regs.h>
> +#include "pci.h"
> +
> +/*
> + * A PCI express designated vendor specific extended capability is defined
> + * in the section 3.7 of Intel scalable I/O virtualization technical spec
> + * for system software and tools to detect endpoint devices supporting the
> + * Intel scalable IO virtualization without host driver dependency.
> + */
> +
> +/**
> + * pci_siov_supported - check if the device can use SIOV
> + * @dev: the PCI device
> + *
> + * Returns true if the device supports SIOV, false otherwise.
> + */
> +bool pci_siov_supported(struct pci_dev *dev)
> +{
> + return pci_find_dvsec(dev, PCI_VENDOR_ID_INTEL, PCI_DVSEC_ID_INTEL_SIOV) < 0 ? false : true;
> +}
> +EXPORT_SYMBOL_GPL(pci_siov_supported);
> +
> +/**
> + * pci_ims_supported - check if the device can use IMS
> + * @dev: the PCI device
> + *
> + * Returns true if the device supports IMS, false otherwise.
> + */
> +bool pci_ims_supported(struct pci_dev *dev)
> +{
> + int pos;
> + u32 caps;
> +
> + pos = pci_find_dvsec(dev, PCI_VENDOR_ID_INTEL, PCI_DVSEC_ID_INTEL_SIOV);
> + if (pos < 0)
> + return false;
> +
> + pci_read_config_dword(dev, pos + PCI_DVSEC_INTEL_SIOV_CAP, &caps);
> + return (caps & PCI_DVSEC_INTEL_SIOV_CAP_IMS) ? true : false;
> +}
> +EXPORT_SYMBOL_GPL(pci_ims_supported);

I don't really see the point of these *_supported() functions. If the
caller wants to use them, I would expect it to call
pci_find_dvsec(PCI_DVSEC_ID_INTEL_SIOV) itself anyway.

But there *are* no calls to pci_find_dvsec(PCI_DVSEC_ID_INTEL_SIOV).
So apparently all you care about is whether the capability *exists*,
and you don't need any information at all from the capability
registers except PCI_DVSEC_INTEL_SIOV_CAP_IMS? That seems a little
weird.

I don't think it's worth adding a whole new file just for this. The
only value the PCI core is adding here is a way to locate the
PCI_DVSEC_ID_INTEL_SIOV capability.

> diff --git a/include/linux/pci-siov.h b/include/linux/pci-siov.h
> new file mode 100644
> index 000000000000..a8a4eb5f4634
> --- /dev/null
> +++ b/include/linux/pci-siov.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef LINUX_PCI_SIOV_H
> +#define LINUX_PCI_SIOV_H
> +
> +#include <linux/pci.h>
> +
> +#ifdef CONFIG_PCI_SIOV
> +/* Scalable I/O Virtualization */
> +bool pci_siov_supported(struct pci_dev *dev);
> +bool pci_ims_supported(struct pci_dev *dev);
> +#else /* CONFIG_PCI_SIOV */
> +static inline bool pci_siov_supported(struct pci_dev *d)
> +{ return false; }
> +static inline bool pci_ims_supported(struct pci_dev *d)
> +{ return false; }
> +#endif /* CONFIG_PCI_SIOV */
> +
> +#endif /* LINUX_PCI_SIOV_H */

What's the benefit to putting these declarations in a separate
pci-siov.h as opposed to putting them in pci.h itself? That's what we
do for things like MSI, IOV, etc.

> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 22207a79762c..4710f09b43b1 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1070,6 +1070,7 @@ int pci_find_next_ext_capability(struct pci_dev *dev, int pos, int cap);
> int pci_find_ht_capability(struct pci_dev *dev, int ht_cap);
> int pci_find_next_ht_capability(struct pci_dev *dev, int pos, int ht_cap);
> struct pci_bus *pci_find_next_bus(const struct pci_bus *from);
> +int pci_find_dvsec(struct pci_dev *dev, u16 vendor, u16 id);
>
> u64 pci_get_dsn(struct pci_dev *dev);
>
> @@ -1726,6 +1727,8 @@ static inline int pci_find_next_capability(struct pci_dev *dev, u8 post,
> { return 0; }
> static inline int pci_find_ext_capability(struct pci_dev *dev, int cap)
> { return 0; }
> +static inline int pci_find_dvsec(struct pci_dev *dev, u16 vendor, u16 id)
> +{ return 0; }
>
> static inline u64 pci_get_dsn(struct pci_dev *dev)
> { return 0; }
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index 8f8bd2318c6c..3532528441ef 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -1071,6 +1071,10 @@
> #define PCI_DVSEC_HEADER1 0x4 /* Designated Vendor-Specific Header1 */
> #define PCI_DVSEC_HEADER2 0x8 /* Designated Vendor-Specific Header2 */
>
> +#define PCI_DVSEC_ID_INTEL_SIOV 0x5
> +#define PCI_DVSEC_INTEL_SIOV_CAP 0x14
> +#define PCI_DVSEC_INTEL_SIOV_CAP_IMS 0x1

Convention in this file is to write constants in the register width,
e.g.,

#define PCI_DVSEC_ID_INTEL_SIOV 0x0005
#define PCI_DVSEC_INTEL_SIOV_CAP_IMS 0x00000001

You can learn this by looking at the surrounding definitions.

> /* Data Link Feature */
> #define PCI_DLF_CAP 0x04 /* Capabilities Register */
> #define PCI_DLF_EXCHANGE_ENABLE 0x80000000 /* Data Link Feature Exchange Enable */
>
>