From 22098763a10d9c1340827fcf6edab66f153b27f0 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 13 Sep 2026 12:27:00 -0700 Subject: Merge tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace Pull tracing fixes from Steven Rostedt: - Don't destroy user event fields when removal fails User event fields are destroyed before the event is removed from visibility. But that can fail leaving the still visible event with no fields. Move the destroying of the fields to after the event is successfully removed from visibility. - Initialize function graph state is fork before calling copy_exec_state() For non-CLONE_VM forks, copy_exec_state() allocates a new task_exec_state. If that allocation fails, ftrace_graph_exit_task() will free the tasks ret_stack pointer. Since that pointer is still using the parent's ret_stack, it mistakenly frees the parent's pointer too. Call ftrace_graph_init() on the task first which will NULL out the new tasks's ret_stack and if the copy fails, it will not free anything. - Remove FGRAPH_MAX_INDEX The macro FGRAPH_MAX_INDEX was added but never used. Remove it. - Save ent_size in function graph printing of nested functions The function graph tracer needs to look at the next event to see if the next event is the return of the current function entry. If it is, it prints a single line: ktime_get(); Otherwise it prints it like a nested function: tick_nohz_irq_exit() { ktime_get(); kcpustat_irq_exit(); } In order to look at the next event, it must save the current event so that it has the information to print from it. It saves the event in the iterator descriptor called "ent". What it doesn't save is the ent_size of the event which is now used to know if the function graph arguments are to be printed. The peek doesn't save the size so the size used happens to be that of the size of the last event that was seen. Save the entry event size in the iterator descriptor so that the correct size is used. - Fix several errors with freeing data in the histogram code The histogram code had a lot of leaked or or incorrect accounting when failures happen. Correct them. - Fix histogram regression of .percent and .graph modifiers Up until 6.3 histogram values could have "percent" or "graph" modifiers that changed how they were printed. But a change that added restricting histograms values from being strings, stack traces and other modifiers inadvertently prevented them from using the percent and graph modifiers, which were legal use cases for values. Put back the percent and graph modifiers. - Fix various typos in the comments - Set the trace_clock before initializing a histogram with clock argument The histogram API allows the user to specific which trace clock to use via a "clock=" string. The histogram is set up first before the clock is checked. If the passed in clock is not valid, it exits without fully fixing up the histogram leaving it on the list and a use-after-free can trigger. Update the clock argument first and if it fails then exit gracefully before the histogram trigger is placed on any lists. - Restore :mod: trailer after parsing in ftrace_set_clr_event The function ftrace_set_clr_event() modifies the parse string and needs to put it back to what was passed in. It searches for ":mod:" via a strsep() but fails to put back the first ':' in the string. Add back the ':' in the passed in string. - Take trace_array reference when opening a tracer options file The options files are dynamically created and some tracers add their own options. When a tracer adds their own list of options, the trace_array holding them has an array to hold the list of options for each tracer. This array increases in size via a krealloc(), and the new entry gets a newly allocated array to hold the options of the new tracer being added. The element in each entry of the tracer's option array holds a pointer back to the trace_array, a pointer to the tracer it is associated to, a pointer to the flags of the option. The issue is that these arrays are freed when the trace_array is freed when its instance it represents is removed from the instances directory. There's a race that an open of one of these options files can happen when the instance is being removed. Add a new helper function to be called by the open function of the options file to iterate all existing trace_arrays under a lock and find the one that has the given option element in one of it's tracer arrays. If found, then update the associated trace_array's reference counter to keep it from being freed. If not found, have the open call return -ENODEV. - Disable interrupts when acquiring the lock in rb_wake_up_waiters() The function rb_wake_up_waiters() assumes it will be called in interrupt context and does not disable irqs when taking cpu_buffer->reader_lock, which can be called in hard interrupt context. The issue is in PREEMPT_RT, this function is called in thread context leaving this lock open to a deadlock. Take the lock with interrupts disabled. - Use rcu_assign_pointer() for tmp_ops filter hash The tmp_ops used in update_ftrace_direct_mod() assigns its filter_hash field directly, but that field is annotated as __rcu and sparse complains. Assign it with rcu_assign_pointer() - Fix use-after-free in enable_trigger_private_data_free() The trace_event_call is accessed through the event_trigger_data's trace_event_file pointer to put the trace_event_call on freeing. The issue is that the trace_event_file data may have been freed already causing a use-after-free. Add a field to the event_trigger_data that points directly to the trace_event_call so that it can decrement its reference directly without needing to go through the trace_event_file. - Fix accounting of buffer data remote headers trace_buffer_desc_size() and trace_remote_alloc_buffer() undercount the number of pages is needed for the asked for size as it doesn't take into account the meta data on each page. Add a helper function to do the calculation properly and use that in these functions. - Catch nr_page_va overflow in ring_buffer_desc sizing The number of pages per remote ring buffer is capped by ring_buffer_desc::nr_page_va (32 bits). A buffer_size large enough to overflow that field would silently allocate a descriptor smaller than what was asked for. - Do not resize the subbuf order if any per_cpu buffer is disabled The mmapping of ring buffers disables resizing the subbuffers, but it is done per-cpu whereas the subbuf size change is done for all the per_cpu buffers under the buffer->mutex. It could change the size of some while the mapping is happening on others. Have the resize of the subbuf order check all the per_cpu buffers under the lock to see if any of them is disabled before starting and causing an inconsistency between buffers that are being mapped. * tag 'trace-v7.3-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace: (25 commits) ring-buffer: Check resize_disabled before publishing the new subbuf order tracing/remotes: Catch nr_page_va overflow in ring_buffer_desc sizing tracing/remotes: Account for ring buffer page header in size calculation tracing: Don't dereference trace_event_file in deferred trigger free ftrace: Use rcu_assign_pointer() for tmp_ops filter hash ring-buffer: Acquire the lock with irqsave in rb_wake_up_waiters() tracing: Take trace_array reference when opening a tracer options file tracing: Fix ring_buffer_read_page_size() kernel-doc tracing: Restore :mod: trailer after parsing in ftrace_set_clr_event() tracing: Fix memory corruption from a "STACKTRACE" histogram key tracing: Fix memory corruption from the histogram stacktrace modifier tracing: Undo the registration when enabling the histogram trigger fails tracing: Take the reference before publishing the named histogram trigger tracing: Set the trace clock before registering the histogram trigger tracing: Fix typo "preceeded" in comment tracing: Fix typo "availabe" in comment tracing: Let histogram values keep the percent and graph modifiers tracing: Keep the entry count when the histogram stats allocation fails tracing: Free histogram the field rejected for a bad modifier tracing: Free histogram the var ref when its initialization fails ... --- Documentation/i2c/functionality.rst | 156 ++++++++++++++++++++++++++++++++++++ 1 file changed, 156 insertions(+) create mode 100644 Documentation/i2c/functionality.rst (limited to 'Documentation/i2c/functionality.rst') diff --git a/Documentation/i2c/functionality.rst b/Documentation/i2c/functionality.rst new file mode 100644 index 000000000..377507c56 --- /dev/null +++ b/Documentation/i2c/functionality.rst @@ -0,0 +1,156 @@ +======================= +I2C/SMBus Functionality +======================= + +INTRODUCTION +------------ + +Because not every I2C or SMBus adapter implements everything in the +I2C specifications, a client can not trust that everything it needs +is implemented when it is given the option to attach to an adapter: +the client needs some way to check whether an adapter has the needed +functionality. + + +FUNCTIONALITY CONSTANTS +----------------------- + +For the most up-to-date list of functionality constants, please check +! + + =============================== ============================================== + I2C_FUNC_I2C Plain i2c-level commands (Pure SMBus + adapters typically can not do these) + I2C_FUNC_10BIT_ADDR Handles the 10-bit address extensions + I2C_FUNC_PROTOCOL_MANGLING Knows about the I2C_M_IGNORE_NAK, + I2C_M_REV_DIR_ADDR and I2C_M_NO_RD_ACK + flags (which modify the I2C protocol!) + I2C_FUNC_NOSTART Can skip repeated start sequence + I2C_FUNC_SMBUS_QUICK Handles the SMBus write_quick command + I2C_FUNC_SMBUS_READ_BYTE Handles the SMBus read_byte command + I2C_FUNC_SMBUS_WRITE_BYTE Handles the SMBus write_byte command + I2C_FUNC_SMBUS_READ_BYTE_DATA Handles the SMBus read_byte_data command + I2C_FUNC_SMBUS_WRITE_BYTE_DATA Handles the SMBus write_byte_data command + I2C_FUNC_SMBUS_READ_WORD_DATA Handles the SMBus read_word_data command + I2C_FUNC_SMBUS_WRITE_WORD_DATA Handles the SMBus write_byte_data command + I2C_FUNC_SMBUS_PROC_CALL Handles the SMBus process_call command + I2C_FUNC_SMBUS_READ_BLOCK_DATA Handles the SMBus read_block_data command + I2C_FUNC_SMBUS_WRITE_BLOCK_DATA Handles the SMBus write_block_data command + I2C_FUNC_SMBUS_READ_I2C_BLOCK Handles the SMBus read_i2c_block_data command + I2C_FUNC_SMBUS_WRITE_I2C_BLOCK Handles the SMBus write_i2c_block_data command + =============================== ============================================== + +A few combinations of the above flags are also defined for your convenience: + + ========================= ====================================== + I2C_FUNC_SMBUS_BYTE Handles the SMBus read_byte + and write_byte commands + I2C_FUNC_SMBUS_BYTE_DATA Handles the SMBus read_byte_data + and write_byte_data commands + I2C_FUNC_SMBUS_WORD_DATA Handles the SMBus read_word_data + and write_word_data commands + I2C_FUNC_SMBUS_BLOCK_DATA Handles the SMBus read_block_data + and write_block_data commands + I2C_FUNC_SMBUS_I2C_BLOCK Handles the SMBus read_i2c_block_data + and write_i2c_block_data commands + I2C_FUNC_SMBUS_EMUL Handles all SMBus commands that can be + emulated by a real I2C adapter (using + the transparent emulation layer) + ========================= ====================================== + +In kernel versions prior to 3.5 I2C_FUNC_NOSTART was implemented as +part of I2C_FUNC_PROTOCOL_MANGLING. + + +ADAPTER IMPLEMENTATION +---------------------- + +When you write a new adapter driver, you will have to implement a +function callback ``functionality``. Typical implementations are given +below. + +A typical SMBus-only adapter would list all the SMBus transactions it +supports. This example comes from the i2c-piix4 driver:: + + static u32 piix4_func(struct i2c_adapter *adapter) + { + return I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | + I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | + I2C_FUNC_SMBUS_BLOCK_DATA; + } + +A typical full-I2C adapter would use the following (from the i2c-pxa +driver):: + + static u32 i2c_pxa_functionality(struct i2c_adapter *adap) + { + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL; + } + +I2C_FUNC_SMBUS_EMUL includes all the SMBus transactions (with the +addition of I2C block transactions) which i2c-core can emulate using +I2C_FUNC_I2C without any help from the adapter driver. The idea is +to let the client drivers check for the support of SMBus functions +without having to care whether the said functions are implemented in +hardware by the adapter, or emulated in software by i2c-core on top +of an I2C adapter. + + +CLIENT CHECKING +--------------- + +Before a client tries to attach to an adapter, or even do tests to check +whether one of the devices it supports is present on an adapter, it should +check whether the needed functionality is present. The typical way to do +this is (from the lm75 driver):: + + static int lm75_detect(...) + { + (...) + if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA | + I2C_FUNC_SMBUS_WORD_DATA)) + goto exit; + (...) + } + +Here, the lm75 driver checks if the adapter can do both SMBus byte data +and SMBus word data transactions. If not, then the driver won't work on +this adapter and there's no point in going on. If the check above is +successful, then the driver knows that it can call the following +functions: i2c_smbus_read_byte_data(), i2c_smbus_write_byte_data(), +i2c_smbus_read_word_data() and i2c_smbus_write_word_data(). As a rule of +thumb, the functionality constants you test for with +i2c_check_functionality() should match exactly the i2c_smbus_* functions +which you driver is calling. + +Note that the check above doesn't tell whether the functionalities are +implemented in hardware by the underlying adapter or emulated in +software by i2c-core. Client drivers don't have to care about this, as +i2c-core will transparently implement SMBus transactions on top of I2C +adapters. + + +CHECKING THROUGH /DEV +--------------------- + +If you try to access an adapter from a userspace program, you will have +to use the /dev interface. You will still have to check whether the +functionality you need is supported, of course. This is done using +the I2C_FUNCS ioctl. An example, adapted from the i2cdetect program, is +below:: + + int file; + if (file = open("/dev/i2c-0", O_RDWR) < 0) { + /* Some kind of error handling */ + exit(1); + } + if (ioctl(file, I2C_FUNCS, &funcs) < 0) { + /* Some kind of error handling */ + exit(1); + } + if (!(funcs & I2C_FUNC_SMBUS_QUICK)) { + /* Oops, the needed functionality (SMBus write_quick function) is + not available! */ + exit(1); + } + /* Now it is safe to use the SMBus write_quick command */ -- cgit v1.3.1