linux-kernel - Re: [PATCH] staging: bcm2835-audio: Fix draining behavior regression

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Date:   Sun, 15 Sep 2019 15:54:16 +0200
From:   Stefan Wahren <wahrenst@....net>
To:     Takashi Iwai <tiwai@...e.de>, Eric Anholt <eric@...olt.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-rpi-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: bcm2835-audio: Fix draining behavior regression

Hi Takashi,

Am 14.09.19 um 17:24 schrieb Takashi Iwai:
> The PCM draining behavior got broken since the recent refactoring, and
> this turned out to be the incorrect expectation of the firmware
> behavior regarding "draining".  While I expected the "drain" flag at
> the stop operation would do processing the queued samples, it seems
> rather dropping the samples.
>
> As a quick fix, just drop the SNDRV_PCM_INFO_DRAIN_TRIGGER flag, so
> that the driver uses the normal PCM draining procedure.  Also, put
> some caution comment to the function for future readers not to fall
> into the same pitfall.
>
> Fixes: d7ca3a71545b ("staging: bcm2835-audio: Operate non-atomic PCM ops")
> BugLink: https://github.com/raspberrypi/linux/issues/2983

thanks for taking care of this. Wouldn't it be better to add the link to
the new comment to provide more context of the unexpected behavior?

Nevertheless:

Acked-by: Stefan Wahren <wahrenst@....net>

> Cc: stable@...r.kernel.org
> Signed-off-by: Takashi Iwai <tiwai@...e.de>
> ---
>  drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c   | 4 ++--
>  drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> index bc1eaa3a0773..826016c3431a 100644
> --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c
> @@ -12,7 +12,7 @@
>  static const struct snd_pcm_hardware snd_bcm2835_playback_hw = {
>  	.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
>  		 SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID |
> -		 SNDRV_PCM_INFO_DRAIN_TRIGGER | SNDRV_PCM_INFO_SYNC_APPLPTR),
> +		 SNDRV_PCM_INFO_SYNC_APPLPTR),
>  	.formats = SNDRV_PCM_FMTBIT_U8 | SNDRV_PCM_FMTBIT_S16_LE,
>  	.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_8000_48000,
>  	.rate_min = 8000,
> @@ -29,7 +29,7 @@ static const struct snd_pcm_hardware snd_bcm2835_playback_hw = {
>  static const struct snd_pcm_hardware snd_bcm2835_playback_spdif_hw = {
>  	.info = (SNDRV_PCM_INFO_INTERLEAVED | SNDRV_PCM_INFO_BLOCK_TRANSFER |
>  		 SNDRV_PCM_INFO_MMAP | SNDRV_PCM_INFO_MMAP_VALID |
> -		 SNDRV_PCM_INFO_DRAIN_TRIGGER | SNDRV_PCM_INFO_SYNC_APPLPTR),
> +		 SNDRV_PCM_INFO_SYNC_APPLPTR),
>  	.formats = SNDRV_PCM_FMTBIT_S16_LE,
>  	.rates = SNDRV_PCM_RATE_CONTINUOUS | SNDRV_PCM_RATE_44100 |
>  	SNDRV_PCM_RATE_48000,
> diff --git a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
> index 23fba01107b9..c6f9cf1913d2 100644
> --- a/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
> +++ b/drivers/staging/vc04_services/bcm2835-audio/bcm2835-vchiq.c
> @@ -289,6 +289,7 @@ int bcm2835_audio_stop(struct bcm2835_alsa_stream *alsa_stream)
>  					 VC_AUDIO_MSG_TYPE_STOP, false);
>  }
>
> +/* FIXME: this doesn't seem working as expected for "draining" */
>  int bcm2835_audio_drain(struct bcm2835_alsa_stream *alsa_stream)
>  {
>  	struct vc_audio_msg m = {