path: root/Documentation/sound/kernel-api
diff options
authorTakashi Iwai <>2019-11-05 09:01:35 +0100
committerTakashi Iwai <>2019-11-06 15:43:18 +0100
commit08422d2c559d1119b17c14e79b2d8ff89f46a356 (patch)
tree7c27ecef45eec6b22677b33a76bd14441c1c4214 /Documentation/sound/kernel-api
parent42ec336f1f9d54049811b749f729e9e01c152ade (diff)
ALSA: memalloc: Allow NULL device for SNDRV_DMA_TYPE_CONTINUOUS type
Currently we pass the artificial device pointer to the allocation helper in the case of SNDRV_DMA_TYPE_CONTINUOUS for passing the GFP flags. But all common cases are the allocations with GFP_KERNEL, and it's messy to put this in each place. In this patch, the memalloc core helper is changed to accept the NULL device pointer and it treats as the default mode, GFP_KERNEL, so that all callers can omit the complex argument but just leave NULL. Link: Signed-off-by: Takashi Iwai <>
Diffstat (limited to 'Documentation/sound/kernel-api')
1 files changed, 8 insertions, 6 deletions
diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
index 132f5eb9b530..5385618fd881 100644
--- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
+++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
@@ -3523,12 +3523,14 @@ The second argument (type) and the third argument (device pointer) are
dependent on the bus. For normal devices, pass the device pointer
(typically identical as ``card->dev``) to the third argument with
``SNDRV_DMA_TYPE_DEV`` type. For the continuous buffer unrelated to the
-bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type and the
-``snd_dma_continuous_data(GFP_KERNEL)`` device pointer, where
-``GFP_KERNEL`` is the kernel allocation flag to use. For the
-scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with the device
-pointer (see the `Non-Contiguous Buffers`_
+bus can be pre-allocated with ``SNDRV_DMA_TYPE_CONTINUOUS`` type.
+You can pass NULL to the device pointer in that case, which is the
+default mode implying to allocate with ``GFP_KRENEL`` flag.
+If you need a different GFP flag, you can pass it by encoding the flag
+into the device pointer via a special macro
+For the scatter-gather buffers, use ``SNDRV_DMA_TYPE_DEV_SG`` with the
+device pointer (see the `Non-Contiguous Buffers`_ section).
Once the buffer is pre-allocated, you can use the allocator in the
``hw_params`` callback: