On 5/22/23 17:01, Bagas Sanjaya wrote:
On Sun, May 21, 2023 at 10:32:16PM +0400, Ivan Orlov wrote:
diff --git a/Documentation/sound/cards/pcmtest.rst b/Documentation/sound/cards/pcmtest.rst
new file mode 100644
index 000000000000..ea8070eaa44e
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+++ b/Documentation/sound/cards/pcmtest.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+The Virtual PCM Test Driver
+===========================
+
+The Virtual PCM Test Driver emulates a generic PCM device, and can be used for
+testing/fuzzing of the userspace ALSA applications, as well as for testing/fuzzing of
+the PCM middle layer. Additionally, it can be used for simulating hard to reproduce
+problems with PCM devices.
+
+What can this driver do?
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+At this moment the driver can do the following things:
+ * Simulate both capture and playback processes
+ * Generate random or pattern-based capturing data
+ * Inject delays into the playback and capturing processes
+ * Inject errors during the PCM callbacks
+
+It supports up to 8 substreams and 4 channels. Also it supports both interleaved and
+non-interleaved access modes.
+
+Also, this driver can check the playback stream for containing the predefined pattern,
+which is used in the corresponding selftest (alsa/test-pcmtest-driver.c). To check the
+PCM middle layer data transferring functionality. Additionally, this driver redefines
"... corresponding selftest ... to check the ..."
+the default RESET ioctl, and the selftest covers this PCM API functionality as well.
+
+Configuration
+-------------
+
+The driver has several parameters besides the common ALSA module parameters:
+
+ * fill_mode (bool) - Buffer fill mode (see below)
+ * inject_delay (int)
+ * inject_hwpars_err (bool)
+ * inject_prepare_err (bool)
+ * inject_trigger_err (bool)
+
+
+Capture Data Generation
+-----------------------
+
+The driver has two modes of data generation: the first (0 in the fill_mode parameter)
+means random data generation, the second (1 in the fill_mode) - pattern-based
+data generation. Let's look at the second mode.
+
+First of all, you may want to specify the pattern for data generation. You can do it
+by writing the pattern to the debugfs file (/sys/kernel/debug/pcmtest/fill_pattern).
+Like that:
"For example::"
+
+.. code-block:: bash
+
+ echo -n mycoolpattern > /sys/kernel/debug/pcmtest/fill_pattern
+
+After this, every capture action performed on the 'pcmtest' device will return
+'mycoolpatternmycoolpatternmycoolpatternmy...' for every channel buffer.
+
+In case of interleaved access, the capture buffer will contain the repeated pattern
+for every channel. Otherwise, every channel buffer will contain the repeated pattern.
+
+The pattern itself can be up to 4096 bytes long.
+
+Delay injection
+---------------
+
+The driver has 'inject_delay' parameter, which has very self-descriptive name and
+can be used for time delay/speedup simulations. The parameter has integer type, and
+it means the delay added between module's internal timer ticks.
+
+If the 'inject_delay' value is positive, the buffer will be filled slower, if it is
+negative - faster. You can try it yourself by starting a recording in any
+audio recording application (like Audacity) and selecting the 'pcmtest' device as a
+source.
+
+This parameter can be also used for generating a huge amount of sound data in a very
+short period of time (with the negative 'inject_delay' value).
+
+Errors injection
+----------------
+
+This module can be used for injecting errors into the PCM communication process. This
+action can help you to figure out how the userspace ALSA program behaves under unusual
+circumstances.
+
+For example, you can make all 'hw_params' PCM callback calls return EBUSY error by
+writing '1' to the 'inject_hwpars_err' module parameter:
+
+.. code-block:: bash
+
+ echo 1 > /sys/module/snd_pcmtest/parameters/inject_hwpars_err
+
+Errors can be injected into the following PCM callbacks:
+
+ * hw_params (EBUSY)
+ * prepare (EINVAL)
+ * trigger (EINVAL)
+
+
+Playback test
+-------------
+
+This driver can be also used for the playback functionality testing - every time you
+write the playback data to the 'pcmtest' PCM device and close it, the driver checks the
+buffer of each channel for containing the looped pattern (which is specified in the
+fill_pattern debugfs file). If the playback buffer content represents the looped pattern,
+'pc_test' debugfs entry is set into '1'. Otherwise, the driver sets it to '0'.
+
+ioctl redefinition test
+-----------------------
+
+The driver redefines the 'reset' ioctl, which is default for all PCM devices. To test
+this functionality, we can trigger the reset ioctl and check the 'ioctl_test' debugfs
+entry:
+
+.. code-block:: bash
+
+ cat /sys/kernel/debug/pcmtest/ioctl_test
+
+If the ioctl is triggered successfully, this file will contain '1', and '0' otherwise.
The rest is LGTM, thanks!
Hi Bagas!
Thank you for the review! I'll fix this in the next version of the patch
set after getting response from the sound maintainers - probably it
isn't the only part which needs to be fixed :)
Kind regards,
Ivan Orlov.
