diff options
| author | Dave Jiang <dave.jiang@intel.com> | 2023-12-21 15:03:39 -0700 |
|---|---|---|
| committer | Dan Williams <dan.j.williams@intel.com> | 2023-12-22 14:53:49 -0800 |
| commit | 4d07a05397c8c15c37c8c3abb7afaea1dcd2f0e7 (patch) | |
| tree | 593e045747cbd9c3a4bc6babe33bb1b3a32f40f8 /drivers/cxl/core/pci.c | |
| parent | 790815902ec61ba1715fd67d3cb9036e13c942bc (diff) | |
cxl: Calculate and store PCI link latency for the downstream ports
The latency is calculated by dividing the flit size over the bandwidth. Add
support to retrieve the flit size for the CXL switch device and calculate
the latency of the PCIe link. Cache the latency number with cxl_dport.
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/170319621931.2212653.6800240203604822886.stgit@djiang5-mobl3
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Diffstat (limited to 'drivers/cxl/core/pci.c')
| -rw-r--r-- | drivers/cxl/core/pci.c | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c index 37e1652afbc7..6c9c8d92f8f7 100644 --- a/drivers/cxl/core/pci.c +++ b/drivers/cxl/core/pci.c @@ -1,5 +1,6 @@ // SPDX-License-Identifier: GPL-2.0-only /* Copyright(c) 2021 Intel Corporation. All rights reserved. */ +#include <linux/units.h> #include <linux/io-64-nonatomic-lo-hi.h> #include <linux/device.h> #include <linux/delay.h> @@ -979,3 +980,38 @@ pci_ers_result_t cxl_error_detected(struct pci_dev *pdev, return PCI_ERS_RESULT_NEED_RESET; } EXPORT_SYMBOL_NS_GPL(cxl_error_detected, CXL); + +static int cxl_flit_size(struct pci_dev *pdev) +{ + if (cxl_pci_flit_256(pdev)) + return 256; + + return 68; +} + +/** + * cxl_pci_get_latency - calculate the link latency for the PCIe link + * @pdev: PCI device + * + * return: calculated latency or 0 for no latency + * + * CXL Memory Device SW Guide v1.0 2.11.4 Link latency calculation + * Link latency = LinkPropagationLatency + FlitLatency + RetimerLatency + * LinkProgationLatency is negligible, so 0 will be used + * RetimerLatency is assumed to be negligible and 0 will be used + * FlitLatency = FlitSize / LinkBandwidth + * FlitSize is defined by spec. CXL rev3.0 4.2.1. + * 68B flit is used up to 32GT/s. >32GT/s, 256B flit size is used. + * The FlitLatency is converted to picoseconds. + */ +long cxl_pci_get_latency(struct pci_dev *pdev) +{ + long bw; + + bw = pcie_link_speed_mbps(pdev); + if (bw < 0) + return 0; + bw /= BITS_PER_BYTE; + + return cxl_flit_size(pdev) * MEGA / bw; +} |