Re: [alsa-devel] [PATCH 1/4] ALSA: memalloc: Allow NULL device for SNDRV_DMA_TYPE_CONTINOUS type

["Amadeusz Sławiński" <amade@asmblr.net>]

On Tue,  5 Nov 2019 09:01:35 +0100
Takashi Iwai <tiwai@suse.de> wrote:

> 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.
> 
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
>  Documentation/sound/kernel-api/writing-an-alsa-driver.rst | 14 ++++++++------
>  sound/core/memalloc.c                                     |  9 ++++++++-
>  2 files changed, 16 insertions(+), 7 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:
> diff --git a/sound/core/memalloc.c b/sound/core/memalloc.c
> index 6850d13aa98c..e56f84fbd659 100644
> --- a/sound/core/memalloc.c
> +++ b/sound/core/memalloc.c
> @@ -99,6 +99,13 @@ static void snd_free_dev_iram(struct snd_dma_buffer *dmab)
>   *
>   */
>  
> +static inline gfp_t snd_mem_get_gfp_flags(const struct device *dev)
> +{
> +	if (!dev)
> +		return GFP_KRENEL;

There is a typo, you remove it in next patch, but it may cause problem
with bisects.


> +	else
> +		return (__force gfp_t)(unsigned long)dev;
> +}
>  
>  /**
>   * snd_dma_alloc_pages - allocate the buffer area according to the given type
> @@ -129,7 +136,7 @@ int snd_dma_alloc_pages(int type, struct device *device, size_t size,
>  	switch (type) {
>  	case SNDRV_DMA_TYPE_CONTINUOUS:
>  		dmab->area = alloc_pages_exact(size,
> -					       (__force gfp_t)(unsigned long)device);
> +					       snd_mem_get_gfp_flags(device));
>  		dmab->addr = 0;
>  		break;
>  #ifdef CONFIG_HAS_DMA

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