Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 191 insertions, 0 deletions

diff --git a/Documentation/driver-api/pwm.rst b/Documentation/driver-api/pwm.rst
new file mode 100644
index 000000000..0d27a40f5
--- /dev/null
+++ b/Documentation/driver-api/pwm.rst
@@ -0,0 +1,191 @@
+======================================
+Pulse Width Modulation (PWM) interface
+======================================
+
+This provides an overview about the Linux PWM interface
+
+PWMs are commonly used for controlling LEDs, fans or vibrators in
+cell phones. PWMs with a fixed purpose have no need implementing
+the Linux PWM API (although they could). However, PWMs are often
+found as discrete devices on SoCs which have no fixed purpose. It's
+up to the board designer to connect them to LEDs or fans. To provide
+this kind of flexibility the generic PWM API exists.
+
+Identifying PWMs
+----------------
+
+Users of the legacy PWM API use unique IDs to refer to PWM devices.
+
+Instead of referring to a PWM device via its unique ID, board setup code
+should instead register a static mapping that can be used to match PWM
+consumers to providers, as given in the following example::
+
+	static struct pwm_lookup board_pwm_lookup[] = {
+		PWM_LOOKUP("tegra-pwm", 0, "pwm-backlight", NULL,
+			   50000, PWM_POLARITY_NORMAL),
+	};
+
+	static void __init board_init(void)
+	{
+		...
+		pwm_add_table(board_pwm_lookup, ARRAY_SIZE(board_pwm_lookup));
+		...
+	}
+
+Using PWMs
+----------
+
+Consumers use the pwm_get() function and pass to it the consumer device or a
+consumer name. pwm_put() is used to free the PWM device. Managed variants of
+the getter, devm_pwm_get() and devm_fwnode_pwm_get(), also exist.
+
+After being requested, a PWM has to be configured using::
+
+	int pwm_apply_might_sleep(struct pwm_device *pwm, struct pwm_state *state);
+
+This API controls both the PWM period/duty_cycle config and the
+enable/disable state.
+
+PWM devices can be used from atomic context, if the PWM does not sleep. You
+can check if this the case with::
+
+        bool pwm_might_sleep(struct pwm_device *pwm);
+
+If false, the PWM can also be configured from atomic context with::
+
+	int pwm_apply_atomic(struct pwm_device *pwm, struct pwm_state *state);
+
+As a consumer, don't rely on the output's state for a disabled PWM. If it's
+easily possible, drivers are supposed to emit the inactive state, but some
+drivers cannot. If you rely on getting the inactive state, use .duty_cycle=0,
+.enabled=true.
+
+There is also a usage_power setting: If set, the PWM driver is only required to
+maintain the power output but has more freedom regarding signal form.
+If supported by the driver, the signal can be optimized, for example to improve
+EMI by phase shifting the individual channels of a chip.
+
+The pwm_config(), pwm_enable() and pwm_disable() functions are just wrappers
+around pwm_apply_might_sleep() and should not be used if the user wants to change
+several parameter at once. For example, if you see pwm_config() and
+pwm_{enable,disable}() calls in the same function, this probably means you
+should switch to pwm_apply_might_sleep().
+
+The PWM user API also allows one to query the PWM state that was passed to the
+last invocation of pwm_apply_might_sleep() using pwm_get_state(). Note this is
+different to what the driver has actually implemented if the request cannot be
+satisfied exactly with the hardware in use. There is currently no way for
+consumers to get the actually implemented settings.
+
+In addition to the PWM state, the PWM API also exposes PWM arguments, which
+are the reference PWM config one should use on this PWM.
+PWM arguments are usually platform-specific and allows the PWM user to only
+care about dutycycle relatively to the full period (like, duty = 50% of the
+period). struct pwm_args contains 2 fields (period and polarity) and should
+be used to set the initial PWM config (usually done in the probe function
+of the PWM user). PWM arguments are retrieved with pwm_get_args().
+
+All consumers should really be reconfiguring the PWM upon resume as
+appropriate. This is the only way to ensure that everything is resumed in
+the proper order.
+
+Using PWMs with the sysfs interface
+-----------------------------------
+
+If CONFIG_SYSFS is enabled in your kernel configuration a simple sysfs
+interface is provided to use the PWMs from userspace. It is exposed at
+/sys/class/pwm/. Each probed PWM controller/chip will be exported as
+pwmchipN, where N is the base of the PWM chip. Inside the directory you
+will find:
+
+  npwm
+    The number of PWM channels this chip supports (read-only).
+
+  export
+    Exports a PWM channel for use with sysfs (write-only).
+
+  unexport
+   Unexports a PWM channel from sysfs (write-only).
+
+The PWM channels are numbered using a per-chip index from 0 to npwm-1.
+
+When a PWM channel is exported a pwmX directory will be created in the
+pwmchipN directory it is associated with, where X is the number of the
+channel that was exported. The following properties will then be available:
+
+  period
+    The total period of the PWM signal (read/write).
+    Value is in nanoseconds and is the sum of the active and inactive
+    time of the PWM.
+
+  duty_cycle
+    The active time of the PWM signal (read/write).
+    Value is in nanoseconds and must be less than or equal to the period.
+
+  polarity
+    Changes the polarity of the PWM signal (read/write).
+    Writes to this property only work if the PWM chip supports changing
+    the polarity.
+    Value is the string "normal" or "inversed".
+
+  enable
+    Enable/disable the PWM signal (read/write).
+
+	- 0 - disabled
+	- 1 - enabled
+
+Implementing a PWM driver
+-------------------------
+
+Currently there are two ways to implement pwm drivers. Traditionally
+there only has been the barebone API meaning that each driver has
+to implement the pwm_*() functions itself. This means that it's impossible
+to have multiple PWM drivers in the system. For this reason it's mandatory
+for new drivers to use the generic PWM framework.
+
+A new PWM controller/chip can be allocated using pwmchip_alloc(), then
+registered using pwmchip_add() and removed again with pwmchip_remove(). To undo
+pwmchip_alloc() use pwmchip_put(). pwmchip_add() takes a filled in struct
+pwm_chip as argument which provides a description of the PWM chip, the number
+of PWM devices provided by the chip and the chip-specific implementation of the
+supported PWM operations to the framework.
+
+When implementing polarity support in a PWM driver, make sure to respect the
+signal conventions in the PWM framework. By definition, normal polarity
+characterizes a signal starts high for the duration of the duty cycle and
+goes low for the remainder of the period. Conversely, a signal with inversed
+polarity starts low for the duration of the duty cycle and goes high for the
+remainder of the period.
+
+Drivers are encouraged to implement ->apply() instead of the legacy
+->enable(), ->disable() and ->config() methods. Doing that should provide
+atomicity in the PWM config workflow, which is required when the PWM controls
+a critical device (like a regulator).
+
+The implementation of ->get_state() (a method used to retrieve initial PWM
+state) is also encouraged for the same reason: letting the PWM user know
+about the current PWM state would allow him to avoid glitches.
+
+Drivers should not implement any power management. In other words,
+consumers should implement it as described in the "Using PWMs" section.
+
+Locking
+-------
+
+The PWM core list manipulations are protected by a mutex, so pwm_get()
+and pwm_put() may not be called from an atomic context.
+Most functions in the PWM consumer API might sleep and so must not be called
+from atomic context. The notable exception is pwm_apply_atomic() which has the
+same semantics as pwm_apply_might_sleep() but can be called from atomic context.
+(The price for that is that it doesn't work for all PWM devices, use
+pwm_might_sleep() to check if a given PWM supports atomic operation.
+
+Locking in the PWM core ensures that callbacks related to a single chip are
+serialized.
+
+Helpers
+-------
+
+Currently a PWM can only be configured with period_ns and duty_ns. For several
+use cases freq_hz and duty_percent might be better. Instead of calculating
+this in your driver please consider adding appropriate helpers to the framework.