Merge tag 'docs-5.15' of git://git.lwn.net/linux

[linux-2.6-microblaze.git] / 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 01d59b8..176b735 100644 (file)
--- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
+++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
@@ -3368,7 +3368,7 @@ This ensures that the device can be closed and the driver unloaded
 without losing data.
 
 This callback is optional. If you do not set ``drain`` in the struct
-snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds
+snd_rawmidi_ops structure, ALSA will simply wait for 50 milliseconds
 instead.
 
 Miscellaneous Devices
@@ -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
 =====================================