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Diffstat (limited to 'Documentation/sound/kernel-api/writing-an-alsa-driver.rst')
| -rw-r--r-- | Documentation/sound/kernel-api/writing-an-alsa-driver.rst | 14 |
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`_ -section). +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 +:c:func:`snd_dma_continuous_data()`. +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: |