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Message-ID: <0a2b9fe6-d8b2-42d6-b6b3-9a94a82c6738@foss.st.com>
Date: Fri, 21 Nov 2025 10:44:12 +0100
From: Arnaud POULIQUEN <arnaud.pouliquen@...s.st.com>
To: Tanmay Shah <tanmay.shah@....com>, <andersson@...nel.org>,
<mathieu.poirier@...aro.org>, <mst@...hat.com>, <jasowang@...hat.com>,
<xuanzhuo@...ux.alibaba.com>, <eperezma@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <linux-remoteproc@...r.kernel.org>,
<virtualization@...ts.linux.dev>, <xiaoxiang@...omi.com>,
Xiang Xiao
<xiaoxiang781216@...il.com>
Subject: Re: [RFC PATCH 2/2] rpmsg: virtio_rpmsg_bus: get buffer size from
config space
On 11/14/25 19:46, Tanmay Shah wrote:
> From: Xiang Xiao <xiaoxiang781216@...il.com>
>
> 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: Xiang Xiao <xiaoxiang@...omi.com>
> Signed-off-by: Tanmay Shah <tanmay.shah@....com>
> ---
> drivers/rpmsg/virtio_rpmsg_bus.c | 68 +++++++++++++++++++++++---------
> include/linux/virtio_rpmsg.h | 24 +++++++++++
> 2 files changed, 74 insertions(+), 18 deletions(-)
> create mode 100644 include/linux/virtio_rpmsg.h
>
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> index cc26dfcc3e29..03dd5535880a 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -25,6 +25,7 @@
> #include <linux/sched.h>
> #include <linux/virtio.h>
> #include <linux/virtio_ids.h>
> +#include <linux/virtio_rpmsg.h>
> #include <linux/virtio_config.h>
> #include <linux/wait.h>
>
> @@ -39,7 +40,8 @@
> * @sbufs: kernel address of tx buffers
> * @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
> + * @rbuf_size: size of one rx buffer
> + * @sbuf_size: size of one 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.
> @@ -60,7 +62,8 @@ struct virtproc_info {
> void *rbufs, *sbufs;
> unsigned int num_rbufs;
> unsigned int num_sbufs;
> - unsigned int buf_size;
> + unsigned int rbuf_size;
> + unsigned int sbuf_size;
> int last_sbuf;
> dma_addr_t bufs_dma;
> struct mutex tx_lock;
> @@ -70,9 +73,6 @@ struct virtproc_info {
> atomic_t sleepers;
> };
>
> -/* 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
> @@ -130,7 +130,7 @@ 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_sbuf < vrp->num_sbufs)
> - ret = vrp->sbufs + vrp->buf_size * vrp->last_sbuf++;
> + ret = vrp->sbufs + vrp->sbuf_size * vrp->last_sbuf++;
> /* or recycle a used one */
> else
> ret = virtqueue_get_buf(vrp->svq, &len);
> @@ -569,7 +569,7 @@ 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->sbuf_size - sizeof(struct rpmsg_hdr)) {
> dev_err(dev, "message is too big (%d)\n", len);
> return -EMSGSIZE;
> }
> @@ -680,7 +680,7 @@ 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->sbuf_size - sizeof(struct rpmsg_hdr);
> }
>
> static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
> @@ -706,7 +706,7 @@ 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->rbuf_size ||
> msg_len > (len - sizeof(struct rpmsg_hdr))) {
> dev_warn(dev, "inbound msg too big: (%d, %d)\n", len, msg_len);
> return -EINVAL;
> @@ -739,7 +739,7 @@ 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->rbuf_size);
>
> /* add the buffer back to the remote processor's virtqueue */
> err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, msg, GFP_KERNEL);
> @@ -888,9 +888,39 @@ static int rpmsg_probe(struct virtio_device *vdev)
> else
> vrp->num_sbufs = 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)) {
> + /* note: virtio_rpmsg_config is defined from remote view */
> + virtio_cread(vdev, struct virtio_rpmsg_config,
> + txbuf_size, &vrp->rbuf_size);
> + virtio_cread(vdev, struct virtio_rpmsg_config,
> + rxbuf_size, &vrp->sbuf_size);
> +
> + /* The buffers must hold rpmsg header atleast */
typo: /* The buffers must hold at least the rpmsg header */
> + if (vrp->rbuf_size < sizeof(struct rpmsg_hdr) ||
> + vrp->sbuf_size < sizeof(struct rpmsg_hdr)) {
> + dev_err(&vdev->dev,
> + "vdev config: rx buf sz = %d, tx buf sz = %d\n",
message could be more explicit: s/"vdev config:/"bad vdev config:/
> + vrp->rbuf_size, vrp->sbuf_size);
> + err = -EINVAL;
> + goto vqs_del;
> + }
> +
> + dev_dbg(&vdev->dev,
> + "vdev config: rx buf sz = 0x%x, tx buf sz = 0x%x\n",
> + vrp->rbuf_size, vrp->sbuf_size);
> + } else {
> + vrp->rbuf_size = DEFAULT_RPMSG_BUF_SIZE;
> + vrp->sbuf_size = DEFAULT_RPMSG_BUF_SIZE;
> + }
>
> - total_buf_space = (vrp->num_rbufs + vrp->num_sbufs) * vrp->buf_size;
> + total_buf_space = (vrp->num_rbufs * vrp->rbuf_size) +
> + (vrp->num_sbufs * vrp->sbuf_size);
> + total_buf_space = ALIGN(total_buf_space, PAGE_SIZE);
Needed? The allocator does not manage the page alignment?
>
> /* allocate coherent memory for the buffers */
> bufs_va = dma_alloc_coherent(vdev->dev.parent,
> @@ -908,14 +938,14 @@ static int rpmsg_probe(struct virtio_device *vdev)
> vrp->rbufs = bufs_va;
>
> /* and second part is dedicated for TX */
> - vrp->sbufs = bufs_va + vrp->num_rbufs * vrp->buf_size;
> + vrp->sbufs = bufs_va + (vrp->num_rbufs * vrp->rbuf_size);
>
> /* set up the receive buffers */
> for (i = 0; i < vrp->num_rbufs; i++) {
> struct scatterlist sg;
> - void *cpu_addr = vrp->rbufs + i * vrp->buf_size;
> + void *cpu_addr = vrp->rbufs + i * vrp->rbuf_size;
>
> - rpmsg_sg_init(&sg, cpu_addr, vrp->buf_size);
> + rpmsg_sg_init(&sg, cpu_addr, vrp->rbuf_size);
>
> err = virtqueue_add_inbuf(vrp->rvq, &sg, 1, cpu_addr,
> GFP_KERNEL);
> @@ -1001,8 +1031,8 @@ 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_rbufs + vrp->num_sbufs;
> - size_t total_buf_space = num_bufs * vrp->buf_size;
> + size_t total_buf_space = (vrp->num_rbufs * vrp->rbuf_size) +
> + (vrp->num_sbufs * vrp->sbuf_size);
> int ret;
>
> virtio_reset_device(vdev);
> @@ -1015,6 +1045,7 @@ static void rpmsg_remove(struct virtio_device *vdev)
>
> vdev->config->del_vqs(vrp->vdev);
>
> + total_buf_space = ALIGN(total_buf_space, PAGE_SIZE);
> dma_free_coherent(vdev->dev.parent, total_buf_space,
> vrp->rbufs, vrp->bufs_dma);
>
> @@ -1028,6 +1059,7 @@ 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/virtio_rpmsg.h b/include/linux/virtio_rpmsg.h
> new file mode 100644
> index 000000000000..6406bc505383
> --- /dev/null
> +++ b/include/linux/virtio_rpmsg.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
This licensing seems reserved for the UAPIs
> +/*
> + * Copyright (C) Pinecone Inc. 2019
> + * Copyright (C) Xiang Xiao <xiaoxiang@...econe.net>
> + */
> +
> +#ifndef _LINUX_VIRTIO_RPMSG_H
> +#define _LINUX_VIRTIO_RPMSG_H
> +
> +#include <linux/types.h>
> +
> +/* The feature bitmap for virtio rpmsg */
> +#define VIRTIO_RPMSG_F_NS 0 /* RP supports name service notifications */
> +#define VIRTIO_RPMSG_F_BUFSZ 2 /* RP get buffer size from config space */
> +
> +struct virtio_rpmsg_config {
> + /* The tx/rx individual buffer size(if VIRTIO_RPMSG_F_BUFSZ) */
> + __u32 txbuf_size;
> + __u32 rxbuf_size;
> + __u32 reserved[14]; /* Reserve for the future use */
> + /* Put the customize config here */
> +} __attribute__((packed));
I am still convinced that adding a version field would help with future
improvements, even though a feature bit field can be used to handle new
configurations. Indeed, how can we address the need for more space
beyond the 14 reserved words?
Thanks,
Arnaud
> +
> +#endif /* _LINUX_VIRTIO_RPMSG_H */
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