From 4352b8aee98005853aa63f57d6377282de17a33f Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 23 Aug 2026 13:28:57 -0700 Subject: Merge tag 'i3c/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linux Pull I3C updates from Alexandre Belloni: "A new driver this cycle, for the AMD AXI I3C controller. There are also new features such as IBI wakeup support, SETAASA device discovery and ACPI support for the the DAA methods, meaning we can now communicate with the SPD devices on DDR5 modules. New driver: - AMD AXI I3C master controller Subsystem: - I3C Common Command Code (CCC) handling improvements, especially around GET CCCs - SETAASA device discovery support - ACPI support for all existing DAA methods like SETDASA, SETNEWDA as well as I2C devices on I3C bus - IBI-based wakeup support Drivers: - dw: SETAASA support - mipi-i3c-hci: advertise IBI wakeup capability, AMD_PT I3C controller support, PIO queue management support for HCI v1.2 - renesas: improve suspend to RAM support, add runtime PM support" * tag 'i3c/for-7.3' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linux: (70 commits) i3c: dw: reduce do_daa time if there's no client i3c: mipi-i3c-hci: Add support for AMD_PT I3C controller i3c: mipi-i3c-hci: Add PIO queue management support for HCI v1.2 i3c: mipi-i3c-hci: Fix missing STAT_IBI_STATUS_THLD in PIO mode i3c: dw: rename "pclk" to "apb" to match dt-binding i3c: dw: make struct dw_i3c_cmd smaller i3c: dw: use COMMAND_PORT_TRANSFER_ARG instead of hardcoding i3c: renesas: Don't register devices when ENTDAA times out i3c: master: dw-i3c-master: fix OD timing for first broadcast i3c: mipi-i3c-hci: Advertise IBI wakeup capability i3c: mipi-i3c-hci: Factor out i3c_hci_sysdev() i3c: mipi-i3c-hci-pci: Propagate I3C wakeup requirements to PCI i3c: master: Reject IBI requests from non-IBI-capable devices i3c: master: Add helper to query bus wakeup requirements i3c: master: Report wakeup events for IBIs i3c: master: Support IBI-based wakeup capability i3c: master: Fix potential UAF in i3c_device_match() i3c: master: Fix potential UAF in i3c_device_uevent() i3c: Make dev->desc locking assumptions explicit i3c: master: Fix use-after-free of master->this ... --- Documentation/networking/driver.rst | 143 ++++++++++++++++++++++++++++++++++++ 1 file changed, 143 insertions(+) create mode 100644 Documentation/networking/driver.rst (limited to 'Documentation/networking/driver.rst') diff --git a/Documentation/networking/driver.rst b/Documentation/networking/driver.rst new file mode 100644 index 000000000..920c0ec98 --- /dev/null +++ b/Documentation/networking/driver.rst @@ -0,0 +1,143 @@ +.. SPDX-License-Identifier: GPL-2.0 + +===================== +Softnet Driver Issues +===================== + +Probing guidelines +================== + +Address validation +------------------ + +Any hardware layer address you obtain for your device should +be verified. For example, for ethernet check it with +linux/etherdevice.h:is_valid_ether_addr() + +Close/stop guidelines +===================== + +Quiescence +---------- + +After the ndo_stop routine has been called, the hardware must +not receive or transmit any data. All in flight packets must +be aborted. If necessary, poll or wait for completion of +any reset commands. + +Auto-close +---------- + +The ndo_stop routine will be called by unregister_netdevice +if device is still UP. + +Transmit path guidelines +======================== + +Stop queues in advance +---------------------- + +The ndo_start_xmit method must not return NETDEV_TX_BUSY under +any normal circumstances. It is considered a hard error unless +there is no way your device can tell ahead of time when its +transmit function will become busy. + +Instead it must maintain the queue properly. For example, +for a driver implementing scatter-gather this means: + +.. code-block:: c + + static u32 drv_tx_avail(struct drv_ring *dr) + { + u32 used = READ_ONCE(dr->prod) - READ_ONCE(dr->cons); + + return dr->tx_ring_size - (used & dr->tx_ring_mask); + } + + static netdev_tx_t drv_hard_start_xmit(struct sk_buff *skb, + struct net_device *dev) + { + struct drv *dp = netdev_priv(dev); + struct netdev_queue *txq; + struct drv_ring *dr; + int idx; + + idx = skb_get_queue_mapping(skb); + dr = dp->tx_rings[idx]; + txq = netdev_get_tx_queue(dev, idx); + + //... + /* This should be a very rare race - log it. */ + if (drv_tx_avail(dr) <= skb_shinfo(skb)->nr_frags + 1) { + netif_tx_stop_queue(txq); + netdev_warn(dev, "Tx Ring full when queue awake!\n"); + return NETDEV_TX_BUSY; + } + + //... queue packet to card ... + + netdev_tx_sent_queue(txq, skb->len); + + //... update tx producer index using WRITE_ONCE() ... + + if (!netif_txq_maybe_stop(txq, drv_tx_avail(dr), + MAX_SKB_FRAGS + 1, 2 * MAX_SKB_FRAGS)) + dr->stats.stopped++; + + //... + return NETDEV_TX_OK; + } + +And then at the end of your TX reclamation event handling: + +.. code-block:: c + + //... update tx consumer index using WRITE_ONCE() ... + + netif_txq_completed_wake(txq, cmpl_pkts, cmpl_bytes, + drv_tx_avail(dr), 2 * MAX_SKB_FRAGS); + +Lockless queue stop / wake helper macros +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. kernel-doc:: include/net/netdev_queues.h + :doc: Lockless queue stopping / waking helpers. + +The standard macros like netif_txq_maybe_stop(), netif_txq_try_stop() etc. +are well tested, prefer them over local synchronization schemes. + +No exclusive ownership +---------------------- + +An ndo_start_xmit method must not modify the shared parts of a +cloned SKB. + +Timely completions +------------------ + +Do not forget that once you return NETDEV_TX_OK from your +ndo_start_xmit method, it is your driver's responsibility to free +up the SKB and in some finite amount of time. + +For example, this means that it is not allowed for your TX +mitigation scheme to let TX packets "hang out" in the TX +ring unreclaimed forever if no new TX packets are sent. +This error can deadlock sockets waiting for send buffer room +to be freed up. + +If you return NETDEV_TX_BUSY from the ndo_start_xmit method, you +must not keep any reference to that SKB and you must not attempt +to free it up. + +Error message reporting +======================= + +A number of driver configuration interfaces pass a Netlink extended ACK +(``extack``) object to the driver (either directly as an argument or +as a member of a parameter struct). The drivers should try to report +most errors via the ``extack`` object. System level exceptions, +indicating that system or device is misbehaving or is in bad state, +should continue to be reported to system logs. + +Messages should be passed **either** via ``extack`` **or** to system logs. +Drivers should not try to report the same information to both. -- cgit v1.3.1