Re: [PATCH v6 9/9] ALSA: virtio: introduce device suspend/resume support

From: Takashi Iwai <tiwai@suse.de>
To: Anton Yakovlev <anton.yakovlev@opensynergy.com>
Cc: <virtualization@lists.linux-foundation.org>,
	<alsa-devel@alsa-project.org>, <virtio-dev@lists.oasis-open.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Jaroslav Kysela <perex@perex.cz>, Takashi Iwai <tiwai@suse.com>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v6 9/9] ALSA: virtio: introduce device suspend/resume support
Date: Sun, 28 Feb 2021 13:05:22 +0100	[thread overview]
Message-ID: <s5hpn0kjt31.wl-tiwai@suse.de> (raw)
In-Reply-To: <20210227085956.1700687-10-anton.yakovlev@opensynergy.com>

On Sat, 27 Feb 2021 09:59:56 +0100,
Anton Yakovlev wrote:
> 
> All running PCM substreams are stopped on device suspend and restarted
> on device resume.
> 
> Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
> ---
>  sound/virtio/virtio_card.c    | 56 +++++++++++++++++++++++++++++++++++
>  sound/virtio/virtio_pcm.c     |  1 +
>  sound/virtio/virtio_pcm_ops.c | 41 ++++++++++++++++++++-----
>  3 files changed, 90 insertions(+), 8 deletions(-)
> 
> diff --git a/sound/virtio/virtio_card.c b/sound/virtio/virtio_card.c
> index 59455a562018..c7ae8801991d 100644
> --- a/sound/virtio/virtio_card.c
> +++ b/sound/virtio/virtio_card.c
> @@ -323,6 +323,58 @@ static void virtsnd_remove(struct virtio_device *vdev)
>  	kfree(snd->event_msgs);
>  }
>  
> +#ifdef CONFIG_PM_SLEEP
> +/**
> + * virtsnd_freeze() - Suspend device.
> + * @vdev: VirtIO parent device.
> + *
> + * Context: Any context.
> + * Return: 0 on success, -errno on failure.
> + */
> +static int virtsnd_freeze(struct virtio_device *vdev)
> +{
> +	struct virtio_snd *snd = vdev->priv;
> +
> +	virtsnd_ctl_msg_cancel_all(snd);
> +
> +	vdev->config->del_vqs(vdev);
> +	vdev->config->reset(vdev);
> +
> +	kfree(snd->event_msgs);
> +
> +	/*
> +	 * If the virtsnd_restore() fails before re-allocating events, then we
> +	 * get a dangling pointer here.
> +	 */
> +	snd->event_msgs = NULL;
> +
> +	return 0;

I suppose some cancel of inflight works is needed?
Ditto for the device removal, too.

> --- a/sound/virtio/virtio_pcm.c
> +++ b/sound/virtio/virtio_pcm.c
> @@ -109,6 +109,7 @@ static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *vss,
>  		SNDRV_PCM_INFO_BATCH |
>  		SNDRV_PCM_INFO_BLOCK_TRANSFER |
>  		SNDRV_PCM_INFO_INTERLEAVED |
> +		SNDRV_PCM_INFO_RESUME |
>  		SNDRV_PCM_INFO_PAUSE;

Actually you don't need to set SNDRV_PCM_INFO_RESUME.
This flag means that the driver supports the full resume procedure,
which isn't often the case; with this, the driver is supposed to
resume the stream exactly from the suspended position.

Most drivers don't set this but implement only the suspend-stop
action.  Then the application (or the sound backend) will re-setup the
stream and restart accordingly.

> @@ -309,6 +318,21 @@ static int virtsnd_pcm_trigger(struct snd_pcm_substream *substream, int command)
>  	int rc;
>  
>  	switch (command) {
> +	case SNDRV_PCM_TRIGGER_RESUME: {
> +		/*
> +		 * We restart the substream by executing the standard command
> +		 * sequence.
> +		 */
> +		rc = virtsnd_pcm_hw_params(substream, NULL);
> +		if (rc)
> +			return rc;
> +
> +		rc = virtsnd_pcm_prepare(substream);
> +		if (rc)
> +			return rc;

And this won't work at all unless nonatomic PCM ops.

thanks,

Takashi