[alsa-devel] [PATCH 2/4] ALSA: compress: Handle errors during avail requests

[Vinod Koul]

On Thu, Mar 10, 2016 at 10:44:52AM +0000, Charles Keepax wrote:
> No errors are currently returned whilst checking the amount of available
> data. If user-space does an avail request which encounters an error it

How do you detect an error? Is DSP sending you error or just fails to
respond? ALso note that in compress formats, DSP may still be decoding the
data and rendering while we thing pointers are not moving

Also while at it, I am thinking exporting snd_compr_stop() might be a better
idea, if you can reliably detect error then stop the stream...

> will generally return zero, causing user-space to poll and if each
> subsequence avail request also returns zero it will wait indefinitely for
> data that is never coming. This patch updates the code so that errors
> during avail requests will be correctly propagated to user-space.
> 
> Signed-off-by: Charles Keepax <ckeepax at opensource.wolfsonmicro.com>
> ---
>  sound/core/compress_offload.c | 64 +++++++++++++++++++++++++++++++------------
>  1 file changed, 47 insertions(+), 17 deletions(-)
> 
> diff --git a/sound/core/compress_offload.c b/sound/core/compress_offload.c
> index 7fac3ca..c9c0849 100644
> --- a/sound/core/compress_offload.c
> +++ b/sound/core/compress_offload.c
> @@ -170,9 +170,15 @@ static int snd_compr_free(struct inode *inode, struct file *f)
>  static int snd_compr_update_tstamp(struct snd_compr_stream *stream,
>  		struct snd_compr_tstamp *tstamp)
>  {
> +	int ret;
> +
>  	if (!stream->ops->pointer)
>  		return -ENOTSUPP;
> -	stream->ops->pointer(stream, tstamp);
> +
> +	ret = stream->ops->pointer(stream, tstamp);
> +	if (ret < 0)
> +		return ret;
> +
>  	pr_debug("dsp consumed till %d total %d bytes\n",
>  		tstamp->byte_offset, tstamp->copied_total);
>  	if (stream->direction == SND_COMPRESS_PLAYBACK)
> @@ -182,18 +188,24 @@ static int snd_compr_update_tstamp(struct snd_compr_stream *stream,
>  	return 0;
>  }
>  
> -static size_t snd_compr_calc_avail(struct snd_compr_stream *stream,
> +static int snd_compr_calc_avail(struct snd_compr_stream *stream,
>  		struct snd_compr_avail *avail)
>  {
> +	int ret;
> +
>  	memset(avail, 0, sizeof(*avail));
> -	snd_compr_update_tstamp(stream, &avail->tstamp);
> +	ret = snd_compr_update_tstamp(stream, &avail->tstamp);
> +	if (ret < 0)
> +		return ret;
> +
>  	/* Still need to return avail even if tstamp can't be filled in */
>  
>  	if (stream->runtime->total_bytes_available == 0 &&
>  			stream->runtime->state == SNDRV_PCM_STATE_SETUP &&
>  			stream->direction == SND_COMPRESS_PLAYBACK) {
>  		pr_debug("detected init and someone forgot to do a write\n");
> -		return stream->runtime->buffer_size;
> +		avail->avail = stream->runtime->buffer_size;
> +		return 0;
>  	}
>  	pr_debug("app wrote %lld, DSP consumed %lld\n",
>  			stream->runtime->total_bytes_available,
> @@ -202,9 +214,11 @@ static size_t snd_compr_calc_avail(struct snd_compr_stream *stream,
>  				stream->runtime->total_bytes_transferred) {
>  		if (stream->direction == SND_COMPRESS_PLAYBACK) {
>  			pr_debug("both pointers are same, returning full avail\n");
> -			return stream->runtime->buffer_size;
> +			avail->avail = stream->runtime->buffer_size;
> +			return 0;
>  		} else {
>  			pr_debug("both pointers are same, returning no avail\n");
> +			avail->avail = 0;
>  			return 0;
>  		}
>  	}
> @@ -215,24 +229,30 @@ static size_t snd_compr_calc_avail(struct snd_compr_stream *stream,
>  		avail->avail = stream->runtime->buffer_size - avail->avail;
>  
>  	pr_debug("ret avail as %lld\n", avail->avail);
> -	return avail->avail;
> +	return 0;
>  }
>  
> -static inline size_t snd_compr_get_avail(struct snd_compr_stream *stream)
> +static inline int snd_compr_get_avail(struct snd_compr_stream *stream,
> +				      size_t *avail)
>  {
> -	struct snd_compr_avail avail;
> +	struct snd_compr_avail full_avail;
> +	int ret;
> +
> +	ret = snd_compr_calc_avail(stream, &full_avail);
> +	*avail = full_avail.avail;
>  
> -	return snd_compr_calc_avail(stream, &avail);
> +	return ret;
>  }
>  
>  static int
>  snd_compr_ioctl_avail(struct snd_compr_stream *stream, unsigned long arg)
>  {
>  	struct snd_compr_avail ioctl_avail;
> -	size_t avail;
> +	int ret;
>  
> -	avail = snd_compr_calc_avail(stream, &ioctl_avail);
> -	ioctl_avail.avail = avail;
> +	ret = snd_compr_calc_avail(stream, &ioctl_avail);
> +	if (ret < 0)
> +		return ret;
>  
>  	if (copy_to_user((__u64 __user *)arg,
>  				&ioctl_avail, sizeof(ioctl_avail)))
> @@ -287,11 +307,14 @@ static ssize_t snd_compr_write(struct file *f, const char __user *buf,
>  	/* write is allowed when stream is running or has been steup */
>  	if (stream->runtime->state != SNDRV_PCM_STATE_SETUP &&
>  			stream->runtime->state != SNDRV_PCM_STATE_RUNNING) {
> -		mutex_unlock(&stream->device->lock);
> -		return -EBADFD;
> +		retval = -EBADFD;
> +		goto out;
>  	}
>  
> -	avail = snd_compr_get_avail(stream);
> +	retval = snd_compr_get_avail(stream, &avail);
> +	if (retval < 0)
> +		goto out;
> +
>  	pr_debug("avail returned %ld\n", (unsigned long)avail);
>  	/* calculate how much we can write to buffer */
>  	if (avail > count)
> @@ -313,6 +336,7 @@ static ssize_t snd_compr_write(struct file *f, const char __user *buf,
>  		pr_debug("stream prepared, Houston we are good to go\n");
>  	}
>  
> +out:
>  	mutex_unlock(&stream->device->lock);
>  	return retval;
>  }
> @@ -346,7 +370,10 @@ static ssize_t snd_compr_read(struct file *f, char __user *buf,
>  		goto out;
>  	}
>  
> -	avail = snd_compr_get_avail(stream);
> +	retval = snd_compr_get_avail(stream, &avail);
> +	if (retval < 0)
> +		goto out;
> +
>  	pr_debug("avail returned %ld\n", (unsigned long)avail);
>  	/* calculate how much we can read from buffer */
>  	if (avail > count)
> @@ -399,7 +426,10 @@ static unsigned int snd_compr_poll(struct file *f, poll_table *wait)
>  	}
>  	poll_wait(f, &stream->runtime->sleep, wait);
>  
> -	avail = snd_compr_get_avail(stream);
> +	retval = snd_compr_get_avail(stream, &avail);
> +	if (retval < 0)
> +		goto out;
> +
>  	pr_debug("avail is %ld\n", (unsigned long)avail);
>  	/* check if we have at least one fragment to fill */
>  	switch (stream->runtime->state) {
> -- 
> 2.1.4
> 
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-- 
~Vinod