Commit f274baa4 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: usb-audio: Allow non-vmalloc buffer for PCM buffers 



Currently, USB-audio driver allocates the PCM buffer via vmalloc(), as
this serves merely as an intermediate buffer that is copied to each
URB transfer buffer.  This works well in general on x86, but on some
archs this may result in cache coherency issues when mmap is used.
OTOH, it works also on such arch unless mmap is used.

This patch is a step for mitigating the inconvenience; a new module
option "use_vmalloc" is provided so that user can choose to allocate
the DMA coherent buffer instead of the existing vmalloc buffer.
The drawback is that it'd be the standard dma_alloc_coherent() calls
and the system would require contiguous pages on non-x86 archs.

Note that it's a global option and not dynamically switchable since
the buffer is pre-allocated at the probe time.  In theory, it's
possible to be switchable, but it'd be trickier and racier.

As default use_vmalloc option is set to true, so that the old behavior
is kept.  For allowing the coherent mmap on ARM or MIPS, pass
use_vmalloc=0 option explicitly.

Reported-and-tested-by: default avatarDaniel Danzberger <daniel@dd-wrt.com>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent f91f1806

Documentation/sound/alsa-configuration.rst

+7 −0
Original line number Diff line number Diff line
@@ -2224,6 +2224,13 @@ quirk_alias 
    Quirk alias list, pass strings like ``0123abcd:5678beef``, which

    applies the existing quirk for the device 5678:beef to a new

    device 0123:abcd.

use_vmalloc

    Use vmalloc() for allocations of the PCM buffers (default: yes).

    For architectures with non-coherent memory like ARM or MIPS, the

    mmap access may give inconsistent results with vmalloc'ed

    buffers.  If mmap is used on such architectures, turn off this

    option, so that the DMA-coherent buffers are allocated and used

    instead.



This module supports multiple devices, autoprobe and hotplugging.

sound/usb/card.c

+4 −0
Original line number Diff line number Diff line
@@ -86,6 +86,8 @@ static bool ignore_ctl_error; 
static bool autoclock = true;

static char *quirk_alias[SNDRV_CARDS];



bool snd_usb_use_vmalloc = true;



module_param_array(index, int, NULL, 0444);

MODULE_PARM_DESC(index, "Index value for the USB audio adapter.");

module_param_array(id, charp, NULL, 0444);
@@ -105,6 +107,8 @@ module_param(autoclock, bool, 0444); 
MODULE_PARM_DESC(autoclock, "Enable auto-clock selection for UAC2 devices (default: yes).");

module_param_array(quirk_alias, charp, NULL, 0444);

MODULE_PARM_DESC(quirk_alias, "Quirk aliases, e.g. 0123abcd:5678beef.");

module_param_named(use_vmalloc, snd_usb_use_vmalloc, bool, 0444);

MODULE_PARM_DESC(use_vmalloc, "Use vmalloc for PCM intermediate buffers (default: yes).");



/*

 * we keep the snd_usb_audio_t instances by ourselves for merging

sound/usb/pcm.c

+54 −5
Original line number Diff line number Diff line
@@ -728,8 +728,12 @@ static int snd_usb_hw_params(struct snd_pcm_substream *substream, 
	struct audioformat *fmt;

	int ret;



	if (snd_usb_use_vmalloc)

		ret = snd_pcm_lib_alloc_vmalloc_buffer(substream,

						       params_buffer_bytes(hw_params));

	else

		ret = snd_pcm_lib_malloc_pages(substream,

					       params_buffer_bytes(hw_params));

	if (ret < 0)

		return ret;
@@ -781,7 +785,11 @@ static int snd_usb_hw_free(struct snd_pcm_substream *substream) 
		snd_usb_endpoint_deactivate(subs->data_endpoint);

		snd_usb_unlock_shutdown(subs->stream->chip);

	}



	if (snd_usb_use_vmalloc)

		return snd_pcm_lib_free_vmalloc_buffer(substream);

	else

		return snd_pcm_lib_free_pages(substream);

}



/*
@@ -1702,9 +1710,50 @@ static const struct snd_pcm_ops snd_usb_capture_ops = { 
	.mmap =		snd_pcm_lib_mmap_vmalloc,

};



static const struct snd_pcm_ops snd_usb_playback_dev_ops = {

	.open =		snd_usb_pcm_open,

	.close =	snd_usb_pcm_close,

	.ioctl =	snd_pcm_lib_ioctl,

	.hw_params =	snd_usb_hw_params,

	.hw_free =	snd_usb_hw_free,

	.prepare =	snd_usb_pcm_prepare,

	.trigger =	snd_usb_substream_playback_trigger,

	.pointer =	snd_usb_pcm_pointer,

	.page =		snd_pcm_sgbuf_ops_page,

};



static const struct snd_pcm_ops snd_usb_capture_dev_ops = {

	.open =		snd_usb_pcm_open,

	.close =	snd_usb_pcm_close,

	.ioctl =	snd_pcm_lib_ioctl,

	.hw_params =	snd_usb_hw_params,

	.hw_free =	snd_usb_hw_free,

	.prepare =	snd_usb_pcm_prepare,

	.trigger =	snd_usb_substream_capture_trigger,

	.pointer =	snd_usb_pcm_pointer,

	.page =		snd_pcm_sgbuf_ops_page,

};



void snd_usb_set_pcm_ops(struct snd_pcm *pcm, int stream)

{

	snd_pcm_set_ops(pcm, stream,

			stream == SNDRV_PCM_STREAM_PLAYBACK ?

			&snd_usb_playback_ops : &snd_usb_capture_ops);

	const struct snd_pcm_ops *ops;



	if (snd_usb_use_vmalloc)

		ops = stream == SNDRV_PCM_STREAM_PLAYBACK ?

			&snd_usb_playback_ops : &snd_usb_capture_ops;

	else

		ops = stream == SNDRV_PCM_STREAM_PLAYBACK ?

			&snd_usb_playback_dev_ops : &snd_usb_capture_dev_ops;

	snd_pcm_set_ops(pcm, stream, ops);

}



void snd_usb_preallocate_buffer(struct snd_usb_substream *subs)

{

	struct snd_pcm *pcm = subs->stream->pcm;

	struct snd_pcm_substream *s = pcm->streams[subs->direction].substream;

	struct device *dev = subs->dev->bus->controller;



	if (!snd_usb_use_vmalloc)

		snd_pcm_lib_preallocate_pages(s, SNDRV_DMA_TYPE_DEV_SG,

					      dev, 64*1024, 512*1024);

}

sound/usb/pcm.h

+1 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ void snd_usb_set_pcm_ops(struct snd_pcm *pcm, int stream); 
int snd_usb_init_pitch(struct snd_usb_audio *chip, int iface,

		       struct usb_host_interface *alts,

		       struct audioformat *fmt);

void snd_usb_preallocate_buffer(struct snd_usb_substream *subs);





#endif /* __USBAUDIO_PCM_H */

sound/usb/stream.c

+2 −0
Original line number Diff line number Diff line
@@ -106,6 +106,8 @@ static void snd_usb_init_substream(struct snd_usb_stream *as, 
	subs->ep_num = fp->endpoint;

	if (fp->channels > subs->channels_max)

		subs->channels_max = fp->channels;



	snd_usb_preallocate_buffer(subs);

}



/* kctl callbacks for usb-audio channel maps */

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