[alsa-devel] [PATCH 0/5] PCM mmap (temporary) fixes for non-coherent architectures

[Benjamin Herrenschmidt]

> A quick patch below (totally untested!) might do that.
> It's passing the device struct blindly, so not sure whether this would
> actually work for all dma_alloc_coherent().

On archs that have dma_ops such as powerpc (but I think x86 too
nowadays) you cannot use the USB device for dma_* operations. You need
to get up to the host controller device...

It -might- be worth looking at adding code to the USB stack to propagate
the parent device dma_ops down to USB devices... hard to tell.

Cheers,
Ben.

> 
> Takashi
> 
> ---
> diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
> index 9edef46..6c82026 100644
> --- a/sound/usb/usbaudio.c
> +++ b/sound/usb/usbaudio.c
> @@ -734,7 +734,7 @@ static void snd_complete_sync_urb(struct urb *urb)
>  	}
>  }
>  
> -
> +#ifdef USBAUDIO_VMALLOC_BUFFER
>  /* get the physical page pointer at the given offset */
>  static struct page *snd_pcm_get_vmalloc_page(struct snd_pcm_substream *subs,
>  					     unsigned long offset)
> @@ -769,6 +769,24 @@ static int snd_pcm_free_vmalloc_buffer(struct snd_pcm_substream *subs)
>  	return 0;
>  }
>  
> +#define preallocate_buffer(chip, pcm, stream) /* NOP */
> +
> +#else
> +#define snd_pcm_get_vmalloc_page	NULL
> +#define snd_pcm_alloc_vmalloc_buffer	snd_pcm_lib_malloc_pages
> +#define snd_pcm_free_vmalloc_buffer	snd_pcm_lib_free_pages
> +
> +static int preallocate_buffer(struct snd_usb_audio *chip, struct snd_pcm *pcm,
> +			      int stream)
> +{
> +	struct snd_pcm_substream *subs = pcm->streams[stream].substream;
> +	if (!subs)
> +		return 0;
> +	return snd_pcm_lib_preallocate_pages(subs, SNDRV_DMA_TYPE_DEV,
> +					     chip->card->dev,
> +					     1024 * 64, 1024 * 1024);
> +}
> +#endif
>  
>  /*
>   * unlink active urbs.
> @@ -2328,6 +2346,7 @@ static int add_audio_endpoint(struct snd_usb_audio *chip, int stream, struct aud
>  		err = snd_pcm_new_stream(as->pcm, stream, 1);
>  		if (err < 0)
>  			return err;
> +		preallocate_buffer(chip, as->pcm, stream);
>  		init_substream(as, stream, fp);
>  		return 0;
>  	}
> @@ -2356,6 +2375,7 @@ static int add_audio_endpoint(struct snd_usb_audio *chip, int stream, struct aud
>  	else
>  		strcpy(pcm->name, "USB Audio");
>  
> +	preallocate_buffer(chip, pcm, stream);
>  	init_substream(as, stream, fp);
>  
>  	list_add(&as->list, &chip->pcm_list);