diff options
Diffstat (limited to 'Documentation/sound')
| -rw-r--r-- | Documentation/sound/alsa-configuration.rst | 3 | ||||
| -rw-r--r-- | Documentation/sound/hd-audio/notes.rst | 6 | ||||
| -rw-r--r-- | Documentation/sound/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/sound/kernel-api/writing-an-alsa-driver.rst | 25 | ||||
| -rw-r--r-- | Documentation/sound/utimers.rst | 126 |
5 files changed, 130 insertions, 31 deletions
diff --git a/Documentation/sound/alsa-configuration.rst b/Documentation/sound/alsa-configuration.rst index 829c672d9fe6..04254474fa04 100644 --- a/Documentation/sound/alsa-configuration.rst +++ b/Documentation/sound/alsa-configuration.rst @@ -1059,6 +1059,9 @@ power_save Automatic power-saving timeout (in second, 0 = disable) power_save_controller Reset HD-audio controller in power-saving mode (default = on) +pm_blacklist + Enable / disable power-management deny-list (default = look up PM + deny-list, 0 = skip PM deny-list, 1 = force to turn off runtime PM) align_buffer_size Force rounding of buffer/period sizes to multiples of 128 bytes. This is more efficient in terms of memory access but isn't diff --git a/Documentation/sound/hd-audio/notes.rst b/Documentation/sound/hd-audio/notes.rst index ef6a4513cce7..e199131bf5ab 100644 --- a/Documentation/sound/hd-audio/notes.rst +++ b/Documentation/sound/hd-audio/notes.rst @@ -321,12 +321,6 @@ Kernel Configuration -------------------- In general, I recommend you to enable the sound debug option, ``CONFIG_SND_DEBUG=y``, no matter whether you are debugging or not. -This enables snd_printd() macro and others, and you'll get additional -kernel messages at probing. - -In addition, you can enable ``CONFIG_SND_DEBUG_VERBOSE=y``. But this -will give you far more messages. Thus turn this on only when you are -sure to want it. Don't forget to turn on the appropriate ``CONFIG_SND_HDA_CODEC_*`` options. Note that each of them corresponds to the codec chip, not diff --git a/Documentation/sound/index.rst b/Documentation/sound/index.rst index 7e67e12730d3..c437f2a4bc85 100644 --- a/Documentation/sound/index.rst +++ b/Documentation/sound/index.rst @@ -13,6 +13,7 @@ Sound Subsystem Documentation alsa-configuration hd-audio/index cards/index + utimers .. only:: subproject and html diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst index 801b0bb57e97..895752cbcedd 100644 --- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst +++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst @@ -4030,31 +4030,6 @@ located in the new subdirectory, sound/pci/xyz. Useful Functions ================ -:c:func:`snd_printk()` and friends ----------------------------------- - -.. note:: This subsection describes a few helper functions for - decorating a bit more on the standard :c:func:`printk()` & co. - However, in general, the use of such helpers is no longer recommended. - If possible, try to stick with the standard functions like - :c:func:`dev_err()` or :c:func:`pr_err()`. - -ALSA provides a verbose version of the :c:func:`printk()` function. -If a kernel config ``CONFIG_SND_VERBOSE_PRINTK`` is set, this function -prints the given message together with the file name and the line of the -caller. The ``KERN_XXX`` prefix is processed as well as the original -:c:func:`printk()` does, so it's recommended to add this prefix, -e.g. snd_printk(KERN_ERR "Oh my, sorry, it's extremely bad!\\n"); - -There are also :c:func:`printk()`'s for debugging. -:c:func:`snd_printd()` can be used for general debugging purposes. -If ``CONFIG_SND_DEBUG`` is set, this function is compiled, and works -just like :c:func:`snd_printk()`. If the ALSA is compiled without -the debugging flag, it's ignored. - -:c:func:`snd_printdd()` is compiled in only when -``CONFIG_SND_DEBUG_VERBOSE`` is set. - :c:func:`snd_BUG()` ------------------- diff --git a/Documentation/sound/utimers.rst b/Documentation/sound/utimers.rst new file mode 100644 index 000000000000..ec21567d3f72 --- /dev/null +++ b/Documentation/sound/utimers.rst @@ -0,0 +1,126 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================= +Userspace-driven timers +======================= + +:Author: Ivan Orlov <ivan.orlov0322@gmail.com> + +Preface +======= + +This document describes the userspace-driven timers: virtual ALSA timers +which could be created and controlled by userspace applications using +IOCTL calls. Such timers could be useful when synchronizing audio +stream with timer sources which we don't have ALSA timers exported for +(e.g. PTP clocks), and when synchronizing the audio stream going through +two virtual sound devices using ``snd-aloop`` (for instance, when +we have a network application sending frames to one snd-aloop device, +and another sound application listening on the other end of snd-aloop). + +Enabling userspace-driven timers +================================ + +The userspace-driven timers could be enabled in the kernel using the +``CONFIG_SND_UTIMER`` configuration option. It depends on the +``CONFIG_SND_TIMER`` option, so it also should be enabled. + +Userspace-driven timers API +=========================== + +Userspace application can create a userspace-driven ALSA timer by +executing the ``SNDRV_TIMER_IOCTL_CREATE`` ioctl call on the +``/dev/snd/timer`` device file descriptor. The ``snd_timer_uinfo`` +structure should be passed as an ioctl argument: + +:: + + struct snd_timer_uinfo { + __u64 resolution; + int fd; + unsigned int id; + unsigned char reserved[16]; + } + +The ``resolution`` field sets the desired resolution in nanoseconds for +the virtual timer. ``resolution`` field simply provides an information +about the virtual timer, but does not affect the timing itself. ``id`` +field gets overwritten by the ioctl, and the identifier you get in this +field after the call can be used as a timer subdevice number when +passing the timer to ``snd-aloop`` kernel module or other userspace +applications. There could be up to 128 userspace-driven timers in the +system at one moment of time, thus the id value ranges from 0 to 127. + +Besides from overwriting the ``snd_timer_uinfo`` struct, ioctl stores +a timer file descriptor, which can be used to trigger the timer, in the +``fd`` field of the ``snd_timer_uinfo`` struct. Allocation of a file +descriptor for the timer guarantees that the timer can only be triggered +by the process which created it. The timer then can be triggered with +``SNDRV_TIMER_IOCTL_TRIGGER`` ioctl call on the timer file descriptor. + +So, the example code for creating and triggering the timer would be: + +:: + + static struct snd_timer_uinfo utimer_info = { + /* Timer is going to tick (presumably) every 1000000 ns */ + .resolution = 1000000ULL, + .id = -1, + }; + + int timer_device_fd = open("/dev/snd/timer", O_RDWR | O_CLOEXEC); + + if (ioctl(timer_device_fd, SNDRV_TIMER_IOCTL_CREATE, &utimer_info)) { + perror("Failed to create the timer"); + return -1; + } + + ... + + /* + * Now we want to trigger the timer. Callbacks of all of the + * timer instances binded to this timer will be executed after + * this call. + */ + ioctl(utimer_info.fd, SNDRV_TIMER_IOCTL_TRIGGER, NULL); + + ... + + /* Now, destroy the timer */ + close(timer_info.fd); + + +More detailed example of creating and ticking the timer could be found +in the utimer ALSA selftest. + +Userspace-driven timers and snd-aloop +------------------------------------- + +Userspace-driven timers could be easily used with ``snd-aloop`` module +when synchronizing two sound applications on both ends of the virtual +sound loopback. For instance, if one of the applications receives sound +frames from network and sends them to snd-aloop pcm device, and another +application listens for frames on the other snd-aloop pcm device, it +makes sense that the ALSA middle layer should initiate a data +transaction when the new period of data is received through network, but +not when the certain amount of jiffies elapses. Userspace-driven ALSA +timers could be used to achieve this. + +To use userspace-driven ALSA timer as a timer source of snd-aloop, pass +the following string as the snd-aloop ``timer_source`` parameter: + +:: + + # modprobe snd-aloop timer_source="-1.4.<utimer_id>" + +Where ``utimer_id`` is the id of the timer you created with +``SNDRV_TIMER_IOCTL_CREATE``, and ``4`` is the number of +userspace-driven timers device (``SNDRV_TIMER_GLOBAL_UDRIVEN``). + +``resolution`` for the userspace-driven ALSA timer used with snd-aloop +should be calculated as ``1000000000ULL / frame_rate * period_size`` as +the timer is going to tick every time a new period of frames is ready. + +After that, each time you trigger the timer with +``SNDRV_TIMER_IOCTL_TRIGGER`` the new period of data will be transferred +from one snd-aloop device to another. |