On Wed, May 20, 2026 at 09:55:33AM -0500, Shah, Tanmay wrote:
>
>
> On 5/20/2026 2:44 AM, Arnaud POULIQUEN wrote:
> >
> >
> > On 5/19/26 19:36, Mathieu Poirier wrote:
> >> On Wed, Apr 29, 2026 at 09:10:52AM -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]>
> >>> ---
> >>>
> >>> Test done:
> >>> - Verify this patch works with the existing firmware
> >>> - Verify this patch works with the firmware that configures
> >>> differt tx & rx buf size
> >>>
> >>> Changes in v2:
> >>> - %s/sbuf_size/tx_buf_size/
> >>> - %s/rbuf_size/rx_buf_size/
> >>> - fix typo
> >>> - do not use ALIGN on buf size, rely on allocator
> >>> - make err msg more explicit, %s/vdev config:/bad vdev config/
> >>> - fix license and add AMD copyrights in the header virtio_rpmsg.h
> >>> - Assign bit 1 to VIRTIO_RPMSG_F_BUFSZ feature
> >>> - use __virtio32 over __u32
> >>> - add version field to virtio rpmsg config structure
> >>> - move linux/virtio_rpmsg.h to linux/rpmsg/virtio_rpmsg.h
> >>>
> >>> drivers/rpmsg/virtio_rpmsg_bus.c | 70 ++++++++++++++++++++++--------
> >>> include/linux/rpmsg/virtio_rpmsg.h | 27 ++++++++++++
> >>> 2 files changed, 79 insertions(+), 18 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 e59d8cf9b975..8116d94413cc 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 buffers for rx
> >>> * @num_tx_buf: total number of buffers for tx
> >>> - * @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_sbuf: 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_sbuf;
> >>> 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.
> >>> @@ -444,7 +444,7 @@ static void *get_a_tx_buf(struct virtproc_info *vrp)
> >>> /* either pick the next unused tx buffer */
> >>> if (vrp->last_sbuf < vrp->num_tx_buf)
> >>> - ret = vrp->tx_bufs + vrp->buf_size * vrp->last_sbuf++;
> >>> + ret = vrp->tx_bufs + vrp->tx_buf_size * vrp->last_sbuf++;
> >>> /* or recycle a used one */
> >>> else
> >>> ret = virtqueue_get_buf(vrp->svq, &len);
> >>> @@ -514,7 +514,7 @@ 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;
> >>> }
> >>> @@ -647,7 +647,7 @@ 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,
> >>> @@ -673,7 +673,7 @@ 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;
> >>> @@ -706,7 +706,7 @@ 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);
> >>> @@ -824,6 +824,7 @@ static int rpmsg_probe(struct virtio_device *vdev)
> >>> int err = 0, i;
> >>> size_t total_buf_space;
> >>> bool notify;
> >>> + u16 version;
> >>> vrp = kzalloc_obj(*vrp);
> >>> if (!vrp)
> >>> @@ -855,9 +856,41 @@ 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)) {
> >>> + /* note: virtio_rpmsg_config is defined from remote view */
> >>> + version = 0;
> >>> + virtio_cread(vdev, struct virtio_rpmsg_config,
> >>> + version, &version);
> >>> + 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);
> >>> +
> >>
> >> A check is also needed to make sure the version received from the
> >> resource table
> >> is '0'.
>
> I think we should start with versaion = 1. So, can I check the version
> number for 1 ?
I've been thinking about that and I agree it should be something else than '0'.
Since we have a u16, I suggest to make bit 15-8 a magic number (surprise us!)
and bit 7-0 the actual version number.
>
> >>
> >>> + /* 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 = %d, tx buf sz = %d\n",
> >>> + vrp->rx_buf_size, vrp->tx_buf_size);
> >>> + err = -EINVAL;
> >>> + goto vqs_del;
> >>> + }
> >>> +
> >>> + dev_dbg(&vdev->dev,
> >>> + "vdev config: version=%d, rx buf sz = 0x%x, tx buf 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,
> >>> @@ -875,14 +908,14 @@ static int rpmsg_probe(struct virtio_device *vdev)
> >>> 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);
> >>> @@ -965,8 +998,8 @@ 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);
> >>> @@ -992,6 +1025,7 @@ 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..285918be68b9
> >>> --- /dev/null
> >>> +++ b/include/linux/rpmsg/virtio_rpmsg.h
> >>> @@ -0,0 +1,27 @@
> >>> +/* SPDX-License-Identifier: GPL-2.0 */
> >>> +/*
> >>> + * Copyright (C) Pinecone Inc. 2019
> >>> + * Copyright (C) Xiang Xiao <[email protected]>
> >>> + * Copyright (C) Advanced Micro Devices, Inc.
> >>> + */
> >>> +
> >>> +#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 */
> >>> +
> >>> +struct virtio_rpmsg_config {
> >>> + __virtio16 version;
> >>> + /* The tx/rx individual buffer size(if VIRTIO_RPMSG_F_BUFSZ) */
> >>> + __virtio32 txbuf_size;
> >>> + __virtio32 rxbuf_size;
> >>> + __virtio32 reserved[14]; /*: Reserve for the future use */
> >>
> >> 66 byte for the configuratio space? I'm puzzled about the
> >> reserved[14], how did
> >> you come up with that number?
>
> I kept the reserved bytes from the original series as it is. The
> original series did not contain version field. With version I don't
> think we need reserved field at all. At best, if we want to append
> padding bytes, then I think __virtio16 reserved; makes sense. That will
> make the structure aligned to 4 byte.
>
> >
> > Is it useful to define the reserved field?
>
> I think reserved field is only useful to keep the structure size aligned
> to 4 bytes.
>
> > The version should allow us to determine the content.
>
> Correct, but I think the structure can be aligned if used correct
> reserved bytes.
>
> > An other solution is to introduce a'size' field to determine the size of
> > the structure:
>
> I think, the resource table already contains config_len field which is
> size of the structure:
>
> https://github.com/torvalds/linux/blob/27fa82620cbaa89a7fc11ac3057701d598813e87/include/linux/remoteproc.h#L275
>
> > struct virtio_rpmsg_config {
> > __virtio16 version;
> > __virtio16 size; /* size of the configuration space */
> > /* The tx/rx individual buffer size(if VIRTIO_RPMSG_F_BUFSZ) */
> > __virtio32 txbuf_size;
> > __virtio32 rxbuf_size;
> > __u8 private[0]; /* customized config */
>
> Do we need customized config? I think I should remove this comment from
> the original patch as well.
>
> Thanks,
> Tanmay
>
> > };
> >
> >>
> >> The rest looks good to me.
> >>
> >
> > Looks good to me too.
> >
> > Thanks,
> > Arnaud
> >
> >>> + /* Put the customize config here */
> >>> +} __packed;
> >>> +
> >>> +#endif /* _LINUX_VIRTIO_RPMSG_H */
> >>> --
> >>> 2.34.1
> >>>
> >
>
