Hi Jay,
These are some minor procedural comments, independent of the larger
design issues.
On Mon, Sep 21, 2015 at 08:47:12AM -0500, Jay Cornwall wrote:
> The PCIe 3.0 AtomicOp (6.15) feature allows atomic transctions to be requested
> by, routed through and completed by PCIe components. Routing and completion
> do not require software support. Component support for each is detectable via
> the DEVCAP2 register.
>
> AtomicOp requests are permitted only if a component's
> DEVCTL2.ATOMICOP_REQUESTER_ENABLE field is set. This capability cannot be
> detected but is a no-op if set on a component with no support. These requests
> can only be serviced if the upstream components support AtomicOp completion
> and/or routing to a component which does.
>
> A concrete example is the AMD Fiji-class GPU, which is specified to support
> AtomicOp requests, routed through a PLX 8747 switch (advertising AtomicOp
> routing) to a Haswell host bridge (advertising AtomicOp completion support).
> When AtomicOp requests are disabled the GPU logs attempts to initiate requests
> to an MMIO register for debugging.
>
> Add pci_enable_atomic_request for per-device control over AtomicOp requests.
> Upstream bridges are checked for AtomicOp routing capability and the call
> fails if any lack this capability. The root port is checked for AtomicOp
> completion capabilities and the call fails if it does not support any.
> Routes to other PCIe components are not checked for AtomicOp routing and
> completion capabilities.
>
> Signed-off-by: Jay Cornwall <jay@xxxxxxxxxxxx>
> ---
> drivers/pci/pci.c | 67 +++++++++++++++++++++++++++++++++++++++++++
> include/linux/pci.h | 1 +
> include/uapi/linux/pci_regs.h | 5 ++++
> 3 files changed, 73 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 6a9a111..58819e4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2453,6 +2453,73 @@ bool pci_acs_path_enabled(struct pci_dev *start,
> }
>
> /**
> + * pci_enable_atomic_request - enable or disable AtomicOp requester
> + * @dev: the PCI device
> + *
> + * Return true if the device is capable of generating AtomicOp requests,
> + * all upstream bridges support AtomicOp routing, and the root port supports
> + * 32-bit, 64-bit and/or 128-bit AtomicOp completion.
> + */
> +bool pci_enable_atomic_request(struct pci_dev *dev)
I'd prefer a "return zero for success or a negative error value (-ENODEV,
etc.)" interface.
> +{
> + struct pci_bus *bus = dev->bus;
> +
> + if (!pci_is_pcie(dev))
> + return false;
> +
> + switch (pci_pcie_type(dev)) {
> + /* PCIe 3.0, 6.15 specifies that endpoints and root ports are permitted
> + * to implement AtomicOp requester capabilities.
> + */
Thanks for the spec references. Since all the references are to the
same section, we might not need to repeat that. Please follow the
comment style in the rest of the file, i.e.,
/*
* Text...
*/
> + case PCI_EXP_TYPE_ENDPOINT:
> + case PCI_EXP_TYPE_LEG_END:
> + case PCI_EXP_TYPE_RC_END:
> + case PCI_EXP_TYPE_ROOT_PORT:
> + break;
> + default:
> + return false;
> + }
> +
> + while (bus->parent) {
> + struct pci_dev *bridge = bus->self;
> + u32 cap;
> +
> + pcie_capability_read_dword(bridge, PCI_EXP_DEVCAP2, &cap);
> +
> + switch (pci_pcie_type(bridge)) {
> + /* PCIe 3.0, 6.15 specifies that upstream, downstream and
> + * root ports may implement AtomicOp routing capabilities.
> + * AtomicOp routing via a root port is not considered here.
> + */
> + case PCI_EXP_TYPE_UPSTREAM:
> + case PCI_EXP_TYPE_DOWNSTREAM:
> + if (!(cap & PCI_EXP_DEVCAP2_ATOMIC_ROUTING))
> + return false;
> + break;
> +
> + /* PCIe 3.0, 6.15 specifies that root ports are permitted to
> + * implement AtomicOp completion capabilities.
> + */
> + case PCI_EXP_TYPE_ROOT_PORT:
> + if (!(cap & (PCI_EXP_DEVCAP2_ATOMIC_COMP32 |
> + PCI_EXP_DEVCAP2_ATOMIC_COMP64 |
> + PCI_EXP_DEVCAP2_ATOMIC_COMP128)))
> + return false;
> + break;
> + }
> +
> +
> + bus = bus->parent;
> + }
> +
> + pcie_capability_set_word(dev, PCI_EXP_DEVCTL2,
> + PCI_EXP_DEVCTL2_ATOMICOP_REQ);
> +
> + return true;
> +}
> +EXPORT_SYMBOL(pci_enable_atomic_request);
> +
> +/**
> * pci_swizzle_interrupt_pin - swizzle INTx for device behind bridge
> * @dev: the PCI device
> * @pin: the INTx pin (1=INTA, 2=INTB, 3=INTC, 4=INTD)
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index e90eb22..755f061 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1801,6 +1801,7 @@ void pci_request_acs(void);
> bool pci_acs_enabled(struct pci_dev *pdev, u16 acs_flags);
> bool pci_acs_path_enabled(struct pci_dev *start,
> struct pci_dev *end, u16 acs_flags);
> +bool pci_enable_atomic_request(struct pci_dev *dev);
>
> #define PCI_VPD_LRDT 0x80 /* Large Resource Data Type */
> #define PCI_VPD_LRDT_ID(x) ((x) | PCI_VPD_LRDT)
> diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> index 413417f..013c2bd 100644
> --- a/include/uapi/linux/pci_regs.h
> +++ b/include/uapi/linux/pci_regs.h
> @@ -571,6 +571,10 @@
> */
> #define PCI_EXP_DEVCAP2 36 /* Device Capabilities 2 */
> #define PCI_EXP_DEVCAP2_ARI 0x00000020 /* Alternative Routing-ID */
> +#define PCI_EXP_DEVCAP2_ATOMIC_ROUTING 0x00000040 /* AtomicOp routing */
> +#define PCI_EXP_DEVCAP2_ATOMIC_COMP32 0x00000080 /* 32b AtomicOp completion */
> +#define PCI_EXP_DEVCAP2_ATOMIC_COMP64 0x00000100 /* 64b AtomicOp completion */
> +#define PCI_EXP_DEVCAP2_ATOMIC_COMP128 0x00000200 /* 128b AtomicOp completion*/
> #define PCI_EXP_DEVCAP2_LTR 0x00000800 /* Latency tolerance reporting */
> #define PCI_EXP_DEVCAP2_OBFF_MASK 0x000c0000 /* OBFF support mechanism */
> #define PCI_EXP_DEVCAP2_OBFF_MSG 0x00040000 /* New message signaling */
> @@ -578,6 +582,7 @@
> #define PCI_EXP_DEVCTL2 40 /* Device Control 2 */
> #define PCI_EXP_DEVCTL2_COMP_TIMEOUT 0x000f /* Completion Timeout Value */
> #define PCI_EXP_DEVCTL2_ARI 0x0020 /* Alternative Routing-ID */
> +#define PCI_EXP_DEVCTL2_ATOMICOP_REQ 0x0040 /* Allow AtomicOp requests */
> #define PCI_EXP_DEVCTL2_IDO_REQ_EN 0x0100 /* Allow IDO for requests */
> #define PCI_EXP_DEVCTL2_IDO_CMP_EN 0x0200 /* Allow IDO for completions */
> #define PCI_EXP_DEVCTL2_LTR_EN 0x0400 /* Enable LTR mechanism */
> --
> 1.9.1
>
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