Re: [RFC PATCH 1/2] rpmsg: virtio_rpmsg_bus: allow the different vring size for send/recv

[Mathieu Poirier <mathieu.poirier@linaro.org>]

Hi Tanmay,

On Fri, Nov 14, 2025 at 10:46:39AM -0800, Tanmay Shah wrote:
> From: Xiang Xiao <xiaoxiang781216@gmail.com>
>

This feature has been abandoned a long time ago - you own it now.
 
> it's useful if the communication throughput is different from each side
> 

Please provide a better changelog.

> Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
> Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
> ---
>  drivers/rpmsg/virtio_rpmsg_bus.c | 47 ++++++++++++++++----------------
>  1 file changed, 24 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 484890b4a6a7..cc26dfcc3e29 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -37,8 +37,9 @@
>   * @svq:	tx virtqueue
>   * @rbufs:	kernel address of rx buffers
>   * @sbufs:	kernel address of tx buffers
> - * @num_bufs:	total number of buffers for rx and tx
> - * @buf_size:   size of one rx or tx buffer
> + * @num_rbufs:	total number of buffers for rx
> + * @num_sbufs:	total number of buffers for tx
> + * @buf_size:	size of one rx or tx buffer
>   * @last_sbuf:	index of last tx buffer used
>   * @bufs_dma:	dma base addr of the buffers
>   * @tx_lock:	protects svq, sbufs and sleepers, to allow concurrent senders.
> @@ -57,7 +58,8 @@ struct virtproc_info {
>  	struct virtio_device *vdev;
>  	struct virtqueue *rvq, *svq;
>  	void *rbufs, *sbufs;
> -	unsigned int num_bufs;
> +	unsigned int num_rbufs;
> +	unsigned int num_sbufs;
>  	unsigned int buf_size;
>  	int last_sbuf;
>  	dma_addr_t bufs_dma;
> @@ -112,7 +114,7 @@ struct virtio_rpmsg_channel {
>  /*
>   * We're allocating buffers of 512 bytes each for communications. The
>   * number of buffers will be computed from the number of buffers supported
> - * by the vring, upto a maximum of 512 buffers (256 in each direction).
> + * by the vring, up to a maximum of 256 in each direction.
>   *
>   * Each buffer will have 16 bytes for the msg header and 496 bytes for
>   * the payload.
> @@ -127,7 +129,7 @@ struct virtio_rpmsg_channel {
>   * can change this without changing anything in the firmware of the remote
>   * processor.
>   */
> -#define MAX_RPMSG_NUM_BUFS	(512)
> +#define MAX_RPMSG_NUM_BUFS	(256)
>  #define MAX_RPMSG_BUF_SIZE	(512)
>  
>  /*
> @@ -439,11 +441,8 @@ static void *get_a_tx_buf(struct virtproc_info *vrp)
>  	/* support multiple concurrent senders */
>  	mutex_lock(&vrp->tx_lock);
>  
> -	/*
> -	 * either pick the next unused tx buffer
> -	 * (half of our buffers are used for sending messages)
> -	 */
> -	if (vrp->last_sbuf < vrp->num_bufs / 2)
> +	/* either pick the next unused tx buffer */
> +	if (vrp->last_sbuf < vrp->num_sbufs)
>  		ret = vrp->sbufs + vrp->buf_size * vrp->last_sbuf++;
>  	/* or recycle a used one */
>  	else
> @@ -878,19 +877,20 @@ static int rpmsg_probe(struct virtio_device *vdev)
>  	vrp->rvq = vqs[0];
>  	vrp->svq = vqs[1];
>  
> -	/* we expect symmetric tx/rx vrings */
> -	WARN_ON(virtqueue_get_vring_size(vrp->rvq) !=
> -		virtqueue_get_vring_size(vrp->svq));
> -
>  	/* we need less buffers if vrings are small */
> -	if (virtqueue_get_vring_size(vrp->rvq) < MAX_RPMSG_NUM_BUFS / 2)
> -		vrp->num_bufs = virtqueue_get_vring_size(vrp->rvq) * 2;
> +	if (virtqueue_get_vring_size(vrp->rvq) < MAX_RPMSG_NUM_BUFS)
> +		vrp->num_rbufs = virtqueue_get_vring_size(vrp->rvq);
> +	else
> +		vrp->num_rbufs = MAX_RPMSG_NUM_BUFS;
> +
> +	if (virtqueue_get_vring_size(vrp->svq) < MAX_RPMSG_NUM_BUFS)
> +		vrp->num_sbufs = virtqueue_get_vring_size(vrp->svq);
>  	else
> -		vrp->num_bufs = MAX_RPMSG_NUM_BUFS;
> +		vrp->num_sbufs = MAX_RPMSG_NUM_BUFS;
>  
>  	vrp->buf_size = MAX_RPMSG_BUF_SIZE;
>  
> -	total_buf_space = vrp->num_bufs * vrp->buf_size;
> +	total_buf_space = (vrp->num_rbufs + vrp->num_sbufs) * vrp->buf_size;
>  
>  	/* allocate coherent memory for the buffers */
>  	bufs_va = dma_alloc_coherent(vdev->dev.parent,
> @@ -904,14 +904,14 @@ static int rpmsg_probe(struct virtio_device *vdev)
>  	dev_dbg(&vdev->dev, "buffers: va %p, dma %pad\n",
>  		bufs_va, &vrp->bufs_dma);
>  
> -	/* half of the buffers is dedicated for RX */
> +	/* first part of the buffers is dedicated for RX */
>  	vrp->rbufs = bufs_va;
>  
> -	/* and half is dedicated for TX */
> -	vrp->sbufs = bufs_va + total_buf_space / 2;
> +	/* and second part is dedicated for TX */
> +	vrp->sbufs = bufs_va + vrp->num_rbufs * vrp->buf_size;
>  
>  	/* set up the receive buffers */
> -	for (i = 0; i < vrp->num_bufs / 2; i++) {
> +	for (i = 0; i < vrp->num_rbufs; i++) {
>  		struct scatterlist sg;
>  		void *cpu_addr = vrp->rbufs + i * vrp->buf_size;
>  
> @@ -1001,7 +1001,8 @@ static int rpmsg_remove_device(struct device *dev, void *data)
>  static void rpmsg_remove(struct virtio_device *vdev)
>  {
>  	struct virtproc_info *vrp = vdev->priv;
> -	size_t total_buf_space = vrp->num_bufs * vrp->buf_size;
> +	unsigned int num_bufs = vrp->num_rbufs + vrp->num_sbufs;
> +	size_t total_buf_space = num_bufs * vrp->buf_size;
>  	int ret;
>  
>  	virtio_reset_device(vdev);
> -- 
> 2.34.1
>