From 27600805e62f800bacf990354632eae4e487d34c Mon Sep 17 00:00:00 2001 From: Yazen Ghannam Date: Thu, 3 Sep 2026 10:43:25 -0500 Subject: x86/amd_node: Fix PCI device reference counting in amd_smn_init() The local "root" pointer is a temporary variable used during the device search. Therefore, refcount related to the search iterators should be cleaned up after the search is complete. Use the __free() cleanup macro to ensure the refcount is decremented when the temporary pointer goes out of scope. Additionally, increment the refcount when caching a root pointer. This ensures the in-use refcount is separate from the temporary search refcounting. Finally, drop the redundant "root = NULL" before the second search loop. The pci_get_class() iterator always decrements the refcount of its "from" argument, so the first loop can only fall through with "root" already NULL. Fixes: 0a4b61d9c2e4 ("x86/amd_node: Fix AMD root device caching") Closes: https://sashiko.dev/#/patchset/20260806160159.230453-1-jason.andryuk%40amd.com Reported-by: Sashiko Assisted-by: LLM Signed-off-by: Yazen Ghannam Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Mario Limonciello (AMD) Cc: Link: https://patch.msgid.link/20260903154325.74343-1-yazen.ghannam@amd.com --- Documentation/driver-api/hsi.rst | 88 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 88 insertions(+) create mode 100644 Documentation/driver-api/hsi.rst (limited to 'Documentation/driver-api/hsi.rst') diff --git a/Documentation/driver-api/hsi.rst b/Documentation/driver-api/hsi.rst new file mode 100644 index 000000000..01b6bebfb --- /dev/null +++ b/Documentation/driver-api/hsi.rst @@ -0,0 +1,88 @@ +High Speed Synchronous Serial Interface (HSI) +============================================= + +Introduction +--------------- + +High Speed Synchronous Interface (HSI) is a full duplex, low latency protocol, +that is optimized for die-level interconnect between an Application Processor +and a Baseband chipset. It has been specified by the MIPI alliance in 2003 and +implemented by multiple vendors since then. + +The HSI interface supports full duplex communication over multiple channels +(typically 8) and is capable of reaching speeds up to 200 Mbit/s. + +The serial protocol uses two signals, DATA and FLAG as combined data and clock +signals and an additional READY signal for flow control. An additional WAKE +signal can be used to wakeup the chips from standby modes. The signals are +commonly prefixed by AC for signals going from the application die to the +cellular die and CA for signals going the other way around. + +:: + + +------------+ +---------------+ + | Cellular | | Application | + | Die | | Die | + | | - - - - - - CAWAKE - - - - - - >| | + | T|------------ CADATA ------------>|R | + | X|------------ CAFLAG ------------>|X | + | |<----------- ACREADY ------------| | + | | | | + | | | | + | |< - - - - - ACWAKE - - - - - - -| | + | R|<----------- ACDATA -------------|T | + | X|<----------- ACFLAG -------------|X | + | |------------ CAREADY ----------->| | + | | | | + | | | | + +------------+ +---------------+ + +HSI Subsystem in Linux +------------------------- + +In the Linux kernel the hsi subsystem is supposed to be used for HSI devices. +The hsi subsystem contains drivers for hsi controllers including support for +multi-port controllers and provides a generic API for using the HSI ports. + +It also contains HSI client drivers, which make use of the generic API to +implement a protocol used on the HSI interface. These client drivers can +use an arbitrary number of channels. + +hsi-char Device +------------------ + +Each port automatically registers a generic client driver called hsi_char, +which provides a character device for userspace representing the HSI port. +It can be used to communicate via HSI from userspace. Userspace may +configure the hsi_char device using the following ioctl commands: + +HSC_RESET + flush the HSI port + +HSC_SET_PM + enable or disable the client. + +HSC_SEND_BREAK + send break + +HSC_SET_RX + set RX configuration + +HSC_GET_RX + get RX configuration + +HSC_SET_TX + set TX configuration + +HSC_GET_TX + get TX configuration + +The kernel HSI API +------------------ + +.. kernel-doc:: include/linux/hsi/hsi.h + :internal: + +.. kernel-doc:: drivers/hsi/hsi_core.c + :export: + -- cgit v1.3.1