On 2026-03-10 at 16:17:30, Björn Töpel ([email protected]) wrote: > Hi! > > Background > ========== > > This series adds a generic ethtool loopback framework with GET/SET > netlink commands, using a component/id/name/direction model that can > (Hopefully! Please refer to "Open questions" below.) represent > loopback points across the network path (MAC, MODULE, PHY, PCS). > > This is the v1 proper of the loopback series, reworked based on > feedback from previous RFC v2 [1]. > > The main change since the RFC v2 is that LOOPBACK_GET no longer > returns an array of entries in a single doit reply. Instead, it uses > the dumpit infrastructure -- each loopback entry is a separate netlink > message in a DUMP response. This follows the same pattern as PHY_GET > and the perphy helpers in net/ethtool/netlink.c, as suggested by > Maxime. > > A filtered DUMP (with a dev-index in the header) lists all loopback > entries for that netdev; an unfiltered DUMP iterates over all netdevs. > The doit handler is also available: when the request includes an > ETHTOOL_A_LOOPBACK_ENTRY nest with component + name, it returns that > specific entry. > > The loopback model remains the same: LOOPBACK_GET/SET with a generic > component/name/direction model that can represent loopback points > across the data path -- MODULE, PHY, MAC, and PCS. This series wires > up MODULE/CMIS and MAC as the first users; PHY and PCS return > -EOPNOTSUPP for now. > > Loopback lookup and enumeration > =============================== > > Each loopback entry is uniquely identified by the tuple (component, > id, name). The kernel provides two GET paths: > > - Exact lookup (doit): the user specifies component + name (and > optionally id) in the request. The kernel dispatches to the right > component handler: for MAC, it calls the driver's > get_loopback(dev, name, id, entry) ethtool_op; for MODULE, it > calls ethtool_cmis_get_loopback(dev, name, entry). Returns a > single entry or -EOPNOTSUPP. > > - Index enumeration (dump): the kernel iterates a flat index space > across all components on a device. Each component's > get_loopback_by_index(dev, index, entry) is tried in order (MAC > first via ethtool_ops, then MODULE/CMIS). The dump stops when all > components return -EOPNOTSUPP. This integrates with the generic > dump_one_dev sub-iterator infrastructure added in patch 1. > > SET takes one or more entries, each with component + name + direction, > and dispatches to the driver's set_loopback() ethtool_op (MAC) or > ethtool_cmis_set_loopback() (MODULE). > > The Common Management Interface Specification (CMIS) defines four > diagnostic loopback types, characterized by location (Host or Media > Side) and signal direction: > > - Host Side Input (Rx->Tx) -- near-end > - Host Side Output (Tx->Rx) -- far-end > - Media Side Input (Rx->Tx) -- near-end > - Media Side Output (Tx->Rx) -- far-end > > Support is detected via Page 13h Byte 128, and loopback is controlled > via Page 13h Bytes 180-183 (one byte per type, one bit per lane). > > The CMIS helpers work entirely over get/set_module_eeprom_by_page, so > any driver that already has EEPROM page access gets module loopback > without new ethtool_ops or driver changes. > > Currently, only mellanox/mlxsw, and broadcom/bnxt support CMIS > operations. I'll follow-up with mlx5 support. > > Implementation > ============== > > Patch 1/11 ethtool: Add dump_one_dev callback for per-device sub-iteration > Replaces the per-PHY specific dump functions with a generic > sub-iterator infrastructure driven by a dump_one_dev callback in > ethnl_request_ops. When ops->dump_one_dev is set, > ethnl_default_start() saves the target device's ifindex for > filtered dumps, and ethnl_default_dumpit() delegates per-device > iteration to the callback. No separate start/dumpit/done functions > are needed. > > Patch 2/11 ethtool: Add loopback netlink UAPI definitions > Adds the YAML spec and generated UAPI header for the new > LOOPBACK_GET/SET commands. Each loopback entry carries a component > type, optional id, name string, supported directions bitmask, and > current direction. > > Patch 3/11 ethtool: Add loopback GET/SET netlink implementation > Implements GET/SET dispatch in a new loopback.c. GET uses the > dump_one_dev infrastructure for dump enumeration (by flat index) > and supports doit exact lookup by (component, id, name) via > parse_request. SET switches on the component and calls the right > handler per entry. No components are wired yet. > > Patch 4/11 ethtool: Add CMIS loopback helpers for module loopback control > Adds cmis_loopback.c with the MODULE component handlers and wires > them into loopback.c's dispatch. GET enumerates entries by index > (ethtool_cmis_get_loopback_by_index) or looks up by name > (ethtool_cmis_get_loopback). SET (ethtool_cmis_set_loopback) > resolves name to control byte indices and enforces mutual > exclusivity. > > Patch 5/11 selftests: drv-net: Add loopback driver test > Adds loopback_drv.py with generic tests that work on any device > with module loopback support: enable/disable, direction switching, > idempotent enable, and rejection while interface is up. > > Patch 6/11 ethtool: Add MAC loopback support via ethtool_ops > Extends struct ethtool_ops with three loopback callbacks for > driver-level MAC loopback: get_loopback (exact lookup by name/id), > get_loopback_by_index (dump enumeration), and set_loopback. Wires > the MAC component into loopback.c's dispatch. For dump enumeration, > MAC entries are tried first, then MODULE/CMIS entries follow at the > next index offset. > > Patch 7/11 netdevsim: Add MAC loopback simulation > Implements the three ethtool loopback ops in netdevsim. Exposes a > single MAC loopback entry ("mac") with both near-end and far-end > support. State is stored in memory and exposed via debugfs under > ethtool/mac_lb/{supported,direction}. > > Patch 8/11 selftests: drv-net: Add MAC loopback netdevsim test > Adds loopback_nsim.py with netdevsim-specific tests for MAC > loopback: entry presence, SET/GET round-trip with debugfs > verification, and error paths. > > Patch 9/11 MAINTAINERS: Add entry for ethtool loopback > Adds a MAINTAINERS entry for the ethtool loopback subsystem covering > the core loopback and CMIS loopback netlink implementation, and the > associated selftests. > > Patch 10/11 netdevsim: Add module EEPROM simulation via debugfs > Adds get/set_module_eeprom_by_page to netdevsim, backed by a > 256-page x 128-byte array exposed via debugfs. > > Patch 11/11 selftests: drv-net: Add CMIS loopback netdevsim test > Extends loopback_nsim.py with netdevsim-specific tests that seed the > EEPROM via debugfs: capability reporting, EEPROM byte verification, > combined MAC + MODULE dump, and error paths. > > Changes since RFC v2 > ==================== > > - Switched LOOPBACK_GET from doit-with-array to dumpit, where each > loopback entry is a separate netlink message. Uses the new generic > dump_one_dev sub-iterator infrastructure instead of duplicating the > perphy dump pattern. (Maxime) > > - u32 to u8 to represent the enums in the YAML. (Maxime) > > - Tried to document the YAML better. (Andrew) > > - Added doit exact lookup by (component, id, name) via > parse_request, so single-entry GET doesn't need a flat index. > > - Added MAC loopback support via three new ethtool_ops callbacks > (get_loopback(), get_loopback_by_index(), set_loopback()) with > netdevsim implementation and tests. > > - Added MAINTAINERS entry. > > Limitations > =========== > > PHY and PCS loopback are defined in the UAPI but not yet implemented. > > No per-lane support -- loopback is all-or-nothing (0xff/0x00) across > lanes. > > Open questions > ============== > > - Is this the right extensibility model? I'd appreciate input from > other NIC vendors on whether component/name/direction is flexible > enough for their loopback implementations. Also, from the PHY/port > folks (Maxime, Russell)! Naveen, please LMK if the MAC side of > thing, is good enough for Marvell.
Hi Bjorn, Is a SERDES component as Maxime suggested something you'd consider for follow-up patches? It would be a natural fit for SoCs with a separate SerDes hardware block. Thanks, Naveen > > - Are patches 10-11 (netdevsim EEPROM simulation + netdevsim-specific > tests) worth carrying? They drive the CMIS Page 13h registers from > debugfs, which gives good coverage without hardware, but it's > another netdevsim surface to maintain. If the consensus is that the > generic driver tests (patch 5) are sufficient, I'm happy to drop > them. > > - Extend mellanox/mlx5 with .set_module_eeprom_by_page() callback. I > got it to work in [6], but would like feedback from the Mellanox > folks. > > Related work > ============ > > [1] Generic loopback support, RFC v2 > https://lore.kernel.org/netdev/[email protected]/ > [2] CMIS loopback, RFC v1 > https://lore.kernel.org/netdev/[email protected]/ > [3] New loopback modes > https://lore.kernel.org/netdev/[email protected]/ > [4] PHY loopback > > https://lore.kernel.org/netdev/[email protected]/ > [5] bnxt_en: add .set_module_eeprom_by_page() support > > https://lore.kernel.org/netdev/[email protected]/ > [6] net/mlx5e: Implement set_module_eeprom_by_page ethtool callback > https://lore.kernel.org/netdev/[email protected]/ > > > Björn Töpel (11): > ethtool: Add dump_one_dev callback for per-device sub-iteration > ethtool: Add loopback netlink UAPI definitions > ethtool: Add loopback GET/SET netlink implementation > ethtool: Add CMIS loopback helpers for module loopback control > selftests: drv-net: Add loopback driver test > ethtool: Add MAC loopback support via ethtool_ops > netdevsim: Add MAC loopback simulation > selftests: drv-net: Add MAC loopback netdevsim test > MAINTAINERS: Add entry for ethtool loopback > netdevsim: Add module EEPROM simulation via debugfs > selftests: drv-net: Add CMIS loopback netdevsim test > > Documentation/netlink/specs/ethtool.yaml | 123 ++++++ > MAINTAINERS | 6 + > drivers/net/netdevsim/ethtool.c | 147 +++++++ > drivers/net/netdevsim/netdevsim.h | 15 + > include/linux/ethtool.h | 23 + > .../uapi/linux/ethtool_netlink_generated.h | 59 +++ > net/ethtool/Makefile | 2 +- > net/ethtool/cmis_loopback.c | 407 ++++++++++++++++++ > net/ethtool/loopback.c | 341 +++++++++++++++ > net/ethtool/mse.c | 1 + > net/ethtool/netlink.c | 285 ++++-------- > net/ethtool/netlink.h | 45 ++ > net/ethtool/phy.c | 1 + > net/ethtool/plca.c | 2 + > net/ethtool/pse-pd.c | 1 + > .../testing/selftests/drivers/net/hw/Makefile | 2 + > .../selftests/drivers/net/hw/loopback_drv.py | 226 ++++++++++ > .../selftests/drivers/net/hw/loopback_nsim.py | 340 +++++++++++++++ > 18 files changed, 1820 insertions(+), 206 deletions(-) > create mode 100644 net/ethtool/cmis_loopback.c > create mode 100644 net/ethtool/loopback.c > create mode 100755 tools/testing/selftests/drivers/net/hw/loopback_drv.py > create mode 100755 tools/testing/selftests/drivers/net/hw/loopback_nsim.py > > > base-commit: 52ede1bce557c66309f41ac29dd190be23ca9129 > -- > 2.53.0 > >
