On Thu, Aug 13, 2026 at 09:42:36PM -0700, Tanmay Shah wrote:
> 512 bytes isn't always suitable for all case, let firmware
> maker decide the best value from resource table.
> enable by VIRTIO_RPMSG_F_BUFSZ feature bit.
>
> Signed-off-by: Tanmay Shah <[email protected]>
> ---
>
> changes in v6:
> - remove buffer alignment from config space
>
> Changes in v5:
>
> - fix documentation about alignment of the buffer size
> - change version field from u16 to u8
> - remove buffer alignment check
> - Separate buffer alignment vs MTU of a single buffer
> - Use buffer alignment only to get next buffer address at alignment
> boundary
>
> Changes in v4:
>
> - Introduce new patch to modify rpmsg.rst documentation
> - check version is always 1.
> - check size field is same as size of struct virtio_rpmsg_config
> - introduce alignment field
> - check alignment field is power of 2
> - check tx and rx buf size is aligned with alignment passed in the
> structure
>
> Changes in v3:
>
> - change version field from u16 to u8
> - introduce size field in the rpmsg_virtio_config structure
> - check version field is set to any non-zero value.
> - check size field is not 0.
> - Remove field for private config, as not needed for now.
> - add documentation of rpmsg_virtio_config structure
>
> drivers/rpmsg/virtio_rpmsg_bus.c | 90 +++++++++++++++++++++++-------
> include/linux/rpmsg/virtio_rpmsg.h | 41 ++++++++++++++
> 2 files changed, 112 insertions(+), 19 deletions(-)
> create mode 100644 include/linux/rpmsg/virtio_rpmsg.h
>
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c
> b/drivers/rpmsg/virtio_rpmsg_bus.c
> index c84b6cec9caf..4235e09dc3b7 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -20,6 +20,7 @@
> #include <linux/rpmsg.h>
> #include <linux/rpmsg/byteorder.h>
> #include <linux/rpmsg/ns.h>
> +#include <linux/rpmsg/virtio_rpmsg.h>
> #include <linux/scatterlist.h>
> #include <linux/slab.h>
> #include <linux/sched.h>
> @@ -39,7 +40,8 @@
> * @tx_bufs: kernel address of tx buffers
> * @num_rx_buf: total number of rx buffers
> * @num_tx_buf: total number of tx buffers
> - * @buf_size: size of one rx or tx buffer
> + * @rx_buf_size: size of one rx buffer
> + * @tx_buf_size: size of one tx buffer
> * @last_tx_buf: index of last tx buffer used
> * @bufs_dma: dma base addr of the buffers
> * @tx_lock: protects svq and tx_bufs, to allow concurrent senders.
> @@ -59,7 +61,8 @@ struct virtproc_info {
> void *rx_bufs, *tx_bufs;
> unsigned int num_rx_buf;
> unsigned int num_tx_buf;
> - unsigned int buf_size;
> + unsigned int rx_buf_size;
> + unsigned int tx_buf_size;
> int last_tx_buf;
> dma_addr_t bufs_dma;
> struct mutex tx_lock;
> @@ -68,9 +71,6 @@ struct virtproc_info {
> wait_queue_head_t sendq;
> };
>
> -/* The feature bitmap for virtio rpmsg */
> -#define VIRTIO_RPMSG_F_NS 0 /* RP supports name service notifications */
> -
> /**
> * struct rpmsg_hdr - common header for all rpmsg messages
> * @src: source address
> @@ -128,7 +128,7 @@ struct virtio_rpmsg_channel {
> * processor.
> */
> #define MAX_RPMSG_NUM_BUFS (256)
> -#define MAX_RPMSG_BUF_SIZE (512)
> +#define DEFAULT_RPMSG_BUF_SIZE (512)
>
> /*
> * Local addresses are dynamically allocated on-demand.
> @@ -443,7 +443,7 @@ static void *get_a_tx_buf(struct virtproc_info *vrp)
>
> /* either pick the next unused tx buffer */
> if (vrp->last_tx_buf < vrp->num_tx_buf)
> - ret = vrp->tx_bufs + vrp->buf_size * vrp->last_tx_buf++;
> + ret = vrp->tx_bufs + vrp->tx_buf_size * vrp->last_tx_buf++;
> /* or recycle a used one */
> else
> ret = virtqueue_get_buf(vrp->svq, &len);
> @@ -513,7 +513,7 @@ static int rpmsg_send_offchannel_raw(struct rpmsg_device
> *rpdev,
> * messaging), or to improve the buffer allocator, to support
> * variable-length buffer sizes.
> */
> - if (len > vrp->buf_size - sizeof(struct rpmsg_hdr)) {
> + if (len > vrp->tx_buf_size - sizeof(struct rpmsg_hdr)) {
> dev_err(dev, "message is too big (%d)\n", len);
> return -EMSGSIZE;
> }
> @@ -646,7 +646,7 @@ static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint
> *ept)
> struct rpmsg_device *rpdev = ept->rpdev;
> struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
>
> - return vch->vrp->buf_size - sizeof(struct rpmsg_hdr);
> + return vch->vrp->tx_buf_size - sizeof(struct rpmsg_hdr);
> }
>
> static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
> @@ -672,7 +672,7 @@ static int rpmsg_recv_single(struct virtproc_info *vrp,
> struct device *dev,
> * We currently use fixed-sized buffers, so trivially sanitize
> * the reported payload length.
> */
> - if (len > vrp->buf_size ||
> + if (len > vrp->rx_buf_size ||
> msg_len > (len - sizeof(struct rpmsg_hdr))) {
> dev_warn(dev, "inbound msg too big: (%d, %d)\n", len, msg_len);
> return -EINVAL;
> @@ -705,7 +705,7 @@ static int rpmsg_recv_single(struct virtproc_info *vrp,
> struct device *dev,
> dev_warn_ratelimited(dev, "msg received with no recipient\n");
>
> /* publish the real size of the buffer */
> - rpmsg_sg_init(&sg, msg, vrp->buf_size);
> + rpmsg_sg_init(&sg, msg, vrp->rx_buf_size);
>
> /* add the buffer back to the remote processor's virtqueue */
> err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, msg, GFP_KERNEL);
> @@ -823,6 +823,8 @@ static int rpmsg_probe(struct virtio_device *vdev)
> int err = 0, i;
> size_t total_buf_space;
> bool notify;
> + u8 version;
> + u16 size;
>
> vrp = kzalloc_obj(*vrp);
> if (!vrp)
> @@ -854,9 +856,59 @@ static int rpmsg_probe(struct virtio_device *vdev)
> else
> vrp->num_tx_buf = MAX_RPMSG_NUM_BUFS;
>
> - vrp->buf_size = MAX_RPMSG_BUF_SIZE;
> + /*
> + * If VIRTIO_RPMSG_F_BUFSZ feature is supported, then configure buf
> + * size from virtio device config space from the resource table.
> + * If the feature is not supported, then assign default buf size.
> + */
> + if (virtio_has_feature(vdev, VIRTIO_RPMSG_F_BUFSZ)) {
> + virtio_cread(vdev, struct virtio_rpmsg_config,
> + version, &version);
> +
> + /* for now we support only v1 */
> + if (version != RPMSG_VDEV_CONFIG_V1) {
> + dev_err(&vdev->dev,
> + "unsupported vdev config version %u\n",
> version);
> + err = -EINVAL;
> + goto vqs_del;
> + }
> +
> + /* size of the config space must match */
> + virtio_cread(vdev, struct virtio_rpmsg_config,
> + size, &size);
> + if (size != sizeof(struct virtio_rpmsg_config)) {
> + dev_err(&vdev->dev, "invalid size of vdev config %u\n",
> + size);
> + err = -EINVAL;
> + goto vqs_del;
> + }
> +
> + /* note: tx and rx are defined from remote view */
> + virtio_cread(vdev, struct virtio_rpmsg_config,
> + txbuf_size, &vrp->rx_buf_size);
> + virtio_cread(vdev, struct virtio_rpmsg_config,
> + rxbuf_size, &vrp->tx_buf_size);
> +
> + /* The buffers must hold at least the rpmsg header */
> + if (vrp->rx_buf_size < sizeof(struct rpmsg_hdr) ||
> + vrp->tx_buf_size < sizeof(struct rpmsg_hdr)) {
> + dev_err(&vdev->dev,
> + "bad vdev config: rx buf sz = %u, tx buf sz =
> %u\n",
> + vrp->rx_buf_size, vrp->tx_buf_size);
> + err = -EINVAL;
> + goto vqs_del;
> + }
> +
> + dev_dbg(&vdev->dev,
> + "vdev config: ver=%u, rx sz = 0x%x, tx sz = 0x%x\n",
> + version, vrp->rx_buf_size, vrp->tx_buf_size);
> + } else {
> + vrp->rx_buf_size = DEFAULT_RPMSG_BUF_SIZE;
> + vrp->tx_buf_size = DEFAULT_RPMSG_BUF_SIZE;
> + }
>
> - total_buf_space = (vrp->num_rx_buf + vrp->num_tx_buf) * vrp->buf_size;
> + total_buf_space = (vrp->num_rx_buf * vrp->rx_buf_size) +
> + (vrp->num_tx_buf * vrp->tx_buf_size);
>
> /* allocate coherent memory for the buffers */
> bufs_va = dma_alloc_coherent(vdev->dev.parent,
> @@ -873,15 +925,14 @@ static int rpmsg_probe(struct virtio_device *vdev)
> /* first part of the buffers is dedicated for RX */
> vrp->rx_bufs = bufs_va;
>
> - /* and second part is dedicated for TX */
> - vrp->tx_bufs = bufs_va + vrp->num_rx_buf * vrp->buf_size;
> + vrp->tx_bufs = bufs_va + (vrp->num_rx_buf * vrp->rx_buf_size);
>
> /* set up the receive buffers */
> for (i = 0; i < vrp->num_rx_buf; i++) {
> struct scatterlist sg;
> - void *cpu_addr = vrp->rx_bufs + i * vrp->buf_size;
> + void *cpu_addr = vrp->rx_bufs + i * vrp->rx_buf_size;
>
> - rpmsg_sg_init(&sg, cpu_addr, vrp->buf_size);
> + rpmsg_sg_init(&sg, cpu_addr, vrp->rx_buf_size);
>
> err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, cpu_addr,
> GFP_KERNEL);
> @@ -964,8 +1015,8 @@ static int rpmsg_remove_device(struct device *dev, void
> *data)
> static void rpmsg_remove(struct virtio_device *vdev)
> {
> struct virtproc_info *vrp = vdev->priv;
> - unsigned int num_bufs = vrp->num_rx_buf + vrp->num_tx_buf;
> - size_t total_buf_space = num_bufs * vrp->buf_size;
> + size_t total_buf_space = (vrp->num_rx_buf * vrp->rx_buf_size) +
> + (vrp->num_tx_buf * vrp->tx_buf_size);
> int ret;
>
> virtio_reset_device(vdev);
> @@ -991,6 +1042,7 @@ static struct virtio_device_id id_table[] = {
>
> static unsigned int features[] = {
> VIRTIO_RPMSG_F_NS,
> + VIRTIO_RPMSG_F_BUFSZ,
> };
>
> static struct virtio_driver virtio_ipc_driver = {
> diff --git a/include/linux/rpmsg/virtio_rpmsg.h
> b/include/linux/rpmsg/virtio_rpmsg.h
> new file mode 100644
> index 000000000000..e28144253a12
> --- /dev/null
> +++ b/include/linux/rpmsg/virtio_rpmsg.h
> @@ -0,0 +1,41 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) Pinecone Inc. 2019
> + * Copyright (C) Xiang Xiao <[email protected]>
> + * Copyright (C) Advanced Micro Devices, Inc. 2026
> + */
> +
> +#ifndef _LINUX_VIRTIO_RPMSG_H
> +#define _LINUX_VIRTIO_RPMSG_H
> +
> +#include <linux/types.h>
> +#include <linux/virtio_types.h>
> +
> +/* The feature bitmap for virtio rpmsg */
> +#define VIRTIO_RPMSG_F_NS 0 /* RP supports name service notifications */
> +#define VIRTIO_RPMSG_F_BUFSZ 1 /* RP get buffer size from config space */
"RP advertises RX/TX buffer sizes from config space"
> +
> +/* Version of struct virtio_rpmsg_config understood by this driver */
> +#define RPMSG_VDEV_CONFIG_V1 1
> +
> +/**
> + * struct virtio_rpmsg_config - config space for rpmsg virtio device
> + *
> + * @version: version of this structure, currently %RPMSG_VDEV_CONFIG_V1.
> + * @size: size of this structure in bytes.
> + * @txbuf_size: Tx buf size from remote's view. For Linux this is rx
> buf size.
> + * @rxbuf_size: Rx buf size from remote's view. For Linux this is tx
> buf size.
> + *
> + * This is the configuration structure shared by the device and the driver,
> + * read when %VIRTIO_RPMSG_F_BUFSZ is negotiated. The fields are laid out so
> + * the structure is naturally 32-bit aligned.
> + */
> +struct virtio_rpmsg_config {
> + u8 version;
> + __virtio16 size;
> + /* The tx/rx individual buffer size (if VIRTIO_RPMSG_F_BUFSZ) */
> + __virtio32 txbuf_size;
> + __virtio32 rxbuf_size;
> +} __packed;
> +
> +#endif /* _LINUX_VIRTIO_RPMSG_H */
> --
> 2.43.0
>
