From ac327f1b10bca6cee8f1a427e5ba451e2d69c710 Mon Sep 17 00:00:00 2001 From: Takashi Iwai Date: Thu, 15 Jul 2021 09:58:26 +0200 Subject: ALSA: doc: Add device-managed resource section Give brief explanations about the device-managed resources and the newly introduced snd_devm_card_new() helper. Link: https://lore.kernel.org/r/20210715075941.23332-5-tiwai@suse.de Signed-off-by: Takashi Iwai --- .../sound/kernel-api/writing-an-alsa-driver.rst | 33 ++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'Documentation/sound/kernel-api/writing-an-alsa-driver.rst') diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst index 01d59b8aea92..255b7d3bebd6 100644 --- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst +++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst @@ -4172,6 +4172,39 @@ module license as GPL, etc., otherwise the system is shown as “tainted”. MODULE_LICENSE("GPL"); +Device-Managed Resources +======================== + +In the examples above, all resources are allocated and released +manually. But human beings are lazy in nature, especially developers +are lazier. So there are some ways to automate the release part; it's +the (device-)managed resources aka devres or devm family. For +example, an object allocated via :c:func:`devm_kmalloc()` will be +freed automatically at unbinding the device. + +ALSA core provides also the device-managed helper, namely, +:c:func:`snd_devm_card_new()` for creating a card object. +Call this functions instead of the normal :c:func:`snd_card_new()`, +and you can forget the explicit :c:func:`snd_card_free()` call, as +it's called automagically at error and removal paths. + +One caveat is that the call of :c:func:`snd_card_free()` would be put +at the beginning of the call chain only after you call +:c:func:`snd_card_register()`. + +Also, the ``private_free`` callback is always called at the card free, +so be careful to put the hardware clean-up procedure in +``private_free`` callback. It might be called even before you +actually set up at an earlier error path. For avoiding such an +invalid initialization, you can set ``private_free`` callback after +:c:func:`snd_card_register()` call succeeds. + +Another thing to be remarked is that you should use device-managed +helpers for each component as much as possible once when you manage +the card in that way. Mixing up with the normal and the managed +resources may screw up the release order. + + How To Put Your Driver Into ALSA Tree ===================================== -- cgit