Hi Tanmay,
On 6/15/26 22:20, 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 v4: squash to virtio rpmsg config patch
- 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 | 129 ++++++++++++++++++++++++-----
include/linux/rpmsg/virtio_rpmsg.h | 50 +++++++++++
2 files changed, 160 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 99df1ae07055..a59925f870a4 100644
--- a/drivers/rpmsg/virtio_rpmsg_bus.c
+++ b/drivers/rpmsg/virtio_rpmsg_bus.c
@@ -15,11 +15,13 @@
#include <linux/idr.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
+#include <linux/log2.h>
#include <linux/module.h>
#include <linux/mutex.h>
#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 +41,8 @@
* @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 +62,8 @@ 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 +72,6 @@ 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 +129,7 @@ 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 +445,7 @@ 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);
@@ -514,7 +515,7 @@ 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 +648,7 @@ 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 +674,7 @@ 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 +707,7 @@ 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);
@@ -820,10 +821,13 @@ static int rpmsg_probe(struct virtio_device *vdev)
struct virtproc_info *vrp;
struct virtio_rpmsg_channel *vch = NULL;
struct rpmsg_device *rpdev_ns, *rpdev_ctrl;
+ u16 rpmsg_buf_align = 0;
void *bufs_va;
int err = 0, i;
size_t total_buf_space;
bool notify;
+ u8 version;
+ u16 size;
vrp = kzalloc_obj(*vrp);
if (!vrp)
@@ -855,9 +859,90 @@ 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;
+ }
- total_buf_space = (vrp->num_rx_buf + vrp->num_tx_buf) * vrp->buf_size;
+ /*
+ * Optional alignment applied to each buffer size and to the TX
+ * buffer base address (e.g. to align buffers on a cache line).
+ * It must be a power of two; zero means no extra alignment.
+ */
+ virtio_cread(vdev, struct virtio_rpmsg_config,
+ rpmsg_buf_align, &rpmsg_buf_align);
+ if (rpmsg_buf_align && !is_power_of_2(rpmsg_buf_align)) {
+ dev_err(&vdev->dev,
+ "bad vdev config: rpmsg_buf_align %u is not a power
of two\n",
+ rpmsg_buf_align);
+ 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;
+ }
+
+ /*
+ * The buffer size must be aligned to the provided alignment for
+ * so that the start address of tx bufs can be aligned.
+ */
'tx' to remove as it also concerns Rx buffers
What about removing this check to manage alignment during buffer allocation?
For example, if the alignment is on a 64-bit address and the tx_buffer
and rx_buffer sizes are 40 bytes, 48 bytes can be allocated in memory
for each buffer, and the virtio descriptor can be filled with aligned
addresses.
In other words, the rpmsg_buf_align field contains the alignment
constraint from the remote processor. If the Linux kernel wants to
impose another alignment constraint, it must test or update
rpmsg_buf_align, but it must not impose alignment on the buffer size.
+ if (rpmsg_buf_align &&
+ (!IS_ALIGNED(vrp->rx_buf_size, rpmsg_buf_align) ||
+ !IS_ALIGNED(vrp->tx_buf_size, rpmsg_buf_align))) {
+ dev_err(&vdev->dev,
+ "bad vdev config: buf sizes (rx %u, tx %u) not
aligned to %u\n",
+ vrp->rx_buf_size, vrp->tx_buf_size,
+ rpmsg_buf_align);
+ err = -EINVAL;
+ goto vqs_del;
+ }
+
+ dev_dbg(&vdev->dev,
+ "vdev config: ver=%u, align=0x%x, rx sz = 0x%x, tx sz =
0x%x\n",
+ version, rpmsg_buf_align, 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->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,
@@ -874,15 +959,20 @@ 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;
+ /*
+ * Here buf_va is aligned to a page. Also rx buf size is aligned with
+ * cache line alignment provided by the firmware, so tx buf's start
+ * address is guranteed to be aligned with the alignment provided by
+ * the firmware.
+ */
+ 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 +1055,8 @@ 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 +1082,7 @@ 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..7e14da68fd17
--- /dev/null
+++ b/include/linux/rpmsg/virtio_rpmsg.h
@@ -0,0 +1,50 @@
+/* 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 */
+
+/* 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.
+ * @reserved: reserved for padding, must be zero.
+ * @size: size of this structure in bytes.
+ * @rpmsg_buf_align: required alignment in bytes for each buffer. Must be a
+ * power of two so that both the buffer sizes and the TX buffer
+ * base address can be aligned (e.g. to a cache line).
+ * @reserved1: reserved for padding, must be zero. Keeps the following 32-bit
+ * fields naturally aligned.
+ * @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;
+ u8 reserved;
Why about defining the version type to u16 to avoid the reserved field?
+ __virtio16 size;
+ __virtio16 rpmsg_buf_align;
+ __virtio16 reserved1;
Seems useless if __packed prevents the compiler from inserting extra padding
bytes between fields,
+ /* The tx/rx individual buffer size (if VIRTIO_RPMSG_F_BUFSZ) */
+ __virtio32 txbuf_size;
+ __virtio32 rxbuf_size;
+} __packed;
proposal
+struct virtio_rpmsg_config {
+ __virtio16 version;
+ __virtio16 size;
+ /* The tx/rx individual buffer size (if VIRTIO_RPMSG_F_BUFSZ) */
+ __virtio32 txbuf_size;
+ __virtio32 rxbuf_size;
+ __virtio16 rpmsg_buf_align;
+} __packed;
+
Regards,
Arnaud
+
+#endif /* _LINUX_VIRTIO_RPMSG_H */
