1 // SPDX-License-Identifier: GPL-2.0
3 * PCI Express Precision Time Measurement
4 * Copyright (c) 2016, Intel Corporation.
7 #include <linux/module.h>
8 #include <linux/init.h>
12 static void pci_ptm_info(struct pci_dev
*dev
)
16 switch (dev
->ptm_granularity
) {
18 snprintf(clock_desc
, sizeof(clock_desc
), "unknown");
21 snprintf(clock_desc
, sizeof(clock_desc
), ">254ns");
24 snprintf(clock_desc
, sizeof(clock_desc
), "%udns",
25 dev
->ptm_granularity
);
28 pci_info(dev
, "PTM enabled%s, %s granularity\n",
29 dev
->ptm_root
? " (root)" : "", clock_desc
);
32 void pci_ptm_init(struct pci_dev
*dev
)
39 if (!pci_is_pcie(dev
))
42 pos
= pci_find_ext_capability(dev
, PCI_EXT_CAP_ID_PTM
);
47 * Enable PTM only on interior devices (root ports, switch ports,
48 * etc.) on the assumption that it causes no link traffic until an
49 * endpoint enables it.
51 if ((pci_pcie_type(dev
) == PCI_EXP_TYPE_ENDPOINT
||
52 pci_pcie_type(dev
) == PCI_EXP_TYPE_RC_END
))
55 pci_read_config_dword(dev
, pos
+ PCI_PTM_CAP
, &cap
);
56 local_clock
= (cap
& PCI_PTM_GRANULARITY_MASK
) >> 8;
59 * There's no point in enabling PTM unless it's enabled in the
60 * upstream device or this device can be a PTM Root itself. Per
61 * the spec recommendation (PCIe r3.1, sec 7.32.3), select the
62 * furthest upstream Time Source as the PTM Root.
64 ups
= pci_upstream_bridge(dev
);
65 if (ups
&& ups
->ptm_enabled
) {
66 ctrl
= PCI_PTM_CTRL_ENABLE
;
67 if (ups
->ptm_granularity
== 0)
68 dev
->ptm_granularity
= 0;
69 else if (ups
->ptm_granularity
> local_clock
)
70 dev
->ptm_granularity
= ups
->ptm_granularity
;
72 if (cap
& PCI_PTM_CAP_ROOT
) {
73 ctrl
= PCI_PTM_CTRL_ENABLE
| PCI_PTM_CTRL_ROOT
;
75 dev
->ptm_granularity
= local_clock
;
80 ctrl
|= dev
->ptm_granularity
<< 8;
81 pci_write_config_dword(dev
, pos
+ PCI_PTM_CTRL
, ctrl
);
87 int pci_enable_ptm(struct pci_dev
*dev
, u8
*granularity
)
93 if (!pci_is_pcie(dev
))
96 pos
= pci_find_ext_capability(dev
, PCI_EXT_CAP_ID_PTM
);
100 pci_read_config_dword(dev
, pos
+ PCI_PTM_CAP
, &cap
);
101 if (!(cap
& PCI_PTM_CAP_REQ
))
105 * For a PCIe Endpoint, PTM is only useful if the endpoint can
106 * issue PTM requests to upstream devices that have PTM enabled.
108 * For Root Complex Integrated Endpoints, there is no upstream
109 * device, so there must be some implementation-specific way to
110 * associate the endpoint with a time source.
112 if (pci_pcie_type(dev
) == PCI_EXP_TYPE_ENDPOINT
) {
113 ups
= pci_upstream_bridge(dev
);
114 if (!ups
|| !ups
->ptm_enabled
)
117 dev
->ptm_granularity
= ups
->ptm_granularity
;
118 } else if (pci_pcie_type(dev
) == PCI_EXP_TYPE_RC_END
) {
119 dev
->ptm_granularity
= 0;
123 ctrl
= PCI_PTM_CTRL_ENABLE
;
124 ctrl
|= dev
->ptm_granularity
<< 8;
125 pci_write_config_dword(dev
, pos
+ PCI_PTM_CTRL
, ctrl
);
126 dev
->ptm_enabled
= 1;
131 *granularity
= dev
->ptm_granularity
;
134 EXPORT_SYMBOL(pci_enable_ptm
);