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Message-ID: <4381ad02-6b4a-a826-1768-ff541663331c@opensynergy.com>
Date: Fri, 25 Feb 2022 19:21:12 +0100
From: Peter Hilber <peter.hilber@...nsynergy.com>
To: Cristian Marussi <cristian.marussi@....com>,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc: sudeep.holla@....com, james.quinlan@...adcom.com,
Jonathan.Cameron@...wei.com, f.fainelli@...il.com,
etienne.carriere@...aro.org, vincent.guittot@...aro.org,
souvik.chakravarty@....com, igor.skalkin@...nsynergy.com,
"Michael S. Tsirkin" <mst@...hat.com>,
virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v5 2/8] firmware: arm_scmi: Review virtio free_list
handling
On 17.02.22 14:12, Cristian Marussi wrote:
> Add a new spinlock dedicated to the access of the TX free list and a couple
> of helpers to get and put messages back and forth from the free_list.
>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: Igor Skalkin <igor.skalkin@...nsynergy.com>
> Cc: Peter Hilber <peter.hilber@...nsynergy.com>
> Cc: virtualization@...ts.linux-foundation.org
> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
Acked-by: Peter Hilber <peter.hilber@...nsynergy.com>
> ---
> drivers/firmware/arm_scmi/virtio.c | 88 +++++++++++++++++++-----------
> 1 file changed, 57 insertions(+), 31 deletions(-)
>
> diff --git a/drivers/firmware/arm_scmi/virtio.c b/drivers/firmware/arm_scmi/virtio.c
> index ed00b072e981..7ec4085cee7e 100644
> --- a/drivers/firmware/arm_scmi/virtio.c
> +++ b/drivers/firmware/arm_scmi/virtio.c
> @@ -40,20 +40,23 @@
> *
> * @vqueue: Associated virtqueue
> * @cinfo: SCMI Tx or Rx channel
> + * @free_lock: Protects access to the @free_list.
> * @free_list: List of unused scmi_vio_msg, maintained for Tx channels only
> * @is_rx: Whether channel is an Rx channel
> * @max_msg: Maximum number of pending messages for this channel.
> - * @lock: Protects access to all members except users.
> + * @lock: Protects access to all members except users, free_list.
> * @shutdown_done: A reference to a completion used when freeing this channel.
> * @users: A reference count to currently active users of this channel.
> */
> struct scmi_vio_channel {
> struct virtqueue *vqueue;
> struct scmi_chan_info *cinfo;
> + /* lock to protect access to the free list. */
> + spinlock_t free_lock;
> struct list_head free_list;
> bool is_rx;
> unsigned int max_msg;
> - /* lock to protect access to all members except users. */
> + /* lock to protect access to all members except users, free_list */
> spinlock_t lock;
> struct completion *shutdown_done;
> refcount_t users;
> @@ -134,18 +137,49 @@ static void scmi_vio_channel_cleanup_sync(struct scmi_vio_channel *vioch)
> wait_for_completion(vioch->shutdown_done);
> }
>
> +/* Assumes to be called with vio channel acquired already */
> +static struct scmi_vio_msg *
> +scmi_virtio_get_free_msg(struct scmi_vio_channel *vioch)
> +{
> + unsigned long flags;
> + struct scmi_vio_msg *msg;
> +
> + spin_lock_irqsave(&vioch->free_lock, flags);
> + if (list_empty(&vioch->free_list)) {
> + spin_unlock_irqrestore(&vioch->free_lock, flags);
> + return NULL;
> + }
> +
> + msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> + list_del_init(&msg->list);
> + spin_unlock_irqrestore(&vioch->free_lock, flags);
> +
> + return msg;
> +}
> +
> +/* Assumes to be called with vio channel acquired already */
> +static void scmi_virtio_put_free_msg(struct scmi_vio_channel *vioch,
> + struct scmi_vio_msg *msg)
> +{
> + unsigned long flags;
> +
> + spin_lock_irqsave(&vioch->free_lock, flags);
> + list_add_tail(&msg->list, &vioch->free_list);
> + spin_unlock_irqrestore(&vioch->free_lock, flags);
> +}
> +
> static bool scmi_vio_have_vq_rx(struct virtio_device *vdev)
> {
> return virtio_has_feature(vdev, VIRTIO_SCMI_F_P2A_CHANNELS);
> }
>
> static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> - struct scmi_vio_msg *msg,
> - struct device *dev)
> + struct scmi_vio_msg *msg)
> {
> struct scatterlist sg_in;
> int rc;
> unsigned long flags;
> + struct device *dev = &vioch->vqueue->vdev->dev;
>
> sg_init_one(&sg_in, msg->input, VIRTIO_SCMI_MAX_PDU_SIZE);
>
> @@ -162,17 +196,17 @@ static int scmi_vio_feed_vq_rx(struct scmi_vio_channel *vioch,
> return rc;
> }
>
> +/*
> + * Assume to be called with channel already acquired or not ready at all;
> + * vioch->lock MUST NOT have been already acquired.
> + */
> static void scmi_finalize_message(struct scmi_vio_channel *vioch,
> struct scmi_vio_msg *msg)
> {
> - if (vioch->is_rx) {
> - scmi_vio_feed_vq_rx(vioch, msg, vioch->cinfo->dev);
> - } else {
> - /* Here IRQs are assumed to be already disabled by the caller */
> - spin_lock(&vioch->lock);
> - list_add(&msg->list, &vioch->free_list);
> - spin_unlock(&vioch->lock);
> - }
> + if (vioch->is_rx)
> + scmi_vio_feed_vq_rx(vioch, msg);
> + else
> + scmi_virtio_put_free_msg(vioch, msg);
> }
>
> static void scmi_vio_complete_cb(struct virtqueue *vqueue)
> @@ -284,7 +318,6 @@ static bool virtio_chan_available(struct device *dev, int idx)
> static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> bool tx)
> {
> - unsigned long flags;
> struct scmi_vio_channel *vioch;
> int index = tx ? VIRTIO_SCMI_VQ_TX : VIRTIO_SCMI_VQ_RX;
> int i;
> @@ -314,13 +347,7 @@ static int virtio_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
> if (!msg->input)
> return -ENOMEM;
>
> - if (tx) {
> - spin_lock_irqsave(&vioch->lock, flags);
> - list_add_tail(&msg->list, &vioch->free_list);
> - spin_unlock_irqrestore(&vioch->lock, flags);
> - } else {
> - scmi_vio_feed_vq_rx(vioch, msg, cinfo->dev);
> - }
> + scmi_finalize_message(vioch, msg);
> }
>
> scmi_vio_channel_ready(vioch, cinfo);
> @@ -354,33 +381,31 @@ static int virtio_send_message(struct scmi_chan_info *cinfo,
> if (!scmi_vio_channel_acquire(vioch))
> return -EINVAL;
>
> - spin_lock_irqsave(&vioch->lock, flags);
> -
> - if (list_empty(&vioch->free_list)) {
> - spin_unlock_irqrestore(&vioch->lock, flags);
> + msg = scmi_virtio_get_free_msg(vioch);
> + if (!msg) {
> scmi_vio_channel_release(vioch);
> return -EBUSY;
> }
>
> - msg = list_first_entry(&vioch->free_list, typeof(*msg), list);
> - list_del(&msg->list);
> -
> msg_tx_prepare(msg->request, xfer);
>
> sg_init_one(&sg_out, msg->request, msg_command_size(xfer));
> sg_init_one(&sg_in, msg->input, msg_response_size(xfer));
>
> + spin_lock_irqsave(&vioch->lock, flags);
> +
> rc = virtqueue_add_sgs(vioch->vqueue, sgs, 1, 1, msg, GFP_ATOMIC);
> - if (rc) {
> - list_add(&msg->list, &vioch->free_list);
> + if (rc)
> dev_err(vioch->cinfo->dev,
> "failed to add to TX virtqueue (%d)\n", rc);
> - } else {
> + else
> virtqueue_kick(vioch->vqueue);
> - }
>
> spin_unlock_irqrestore(&vioch->lock, flags);
>
> + if (rc)
> + scmi_virtio_put_free_msg(vioch, msg);
> +
> scmi_vio_channel_release(vioch);
>
> return rc;
> @@ -457,6 +482,7 @@ static int scmi_vio_probe(struct virtio_device *vdev)
> unsigned int sz;
>
> spin_lock_init(&channels[i].lock);
> + spin_lock_init(&channels[i].free_lock);
> INIT_LIST_HEAD(&channels[i].free_list);
> channels[i].vqueue = vqs[i];
>
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