On 5/21/2026 11:58 AM, Mathieu Poirier wrote:
> On Thu, 21 May 2026 at 09:08, Shah, Tanmay <[email protected]> wrote:
>>
>>
>>
>> On 5/20/2026 10:43 AM, Arnaud POULIQUEN wrote:
>>>
>>>
>>> On 5/20/26 16:55, 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 ?
>>>>
>>>>>>
>>>>>>> + /* 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
>>>
>>>
>>> The resource table is the solution for the remoteproc virtio backend,
>>> The solution should be able to work with some other virtio backends.
>>> In such case we can not rely on the resource table.
>>>
>>
>> For now we have only the remoteproc virtio backend. If we ever introduce
>> new backend, then can we update this structure with new 'version' num
>> and include size field at that time? Since, now there is no real use of it.
>>
>>> The resource table is a solution for the remoteproc virtio backend.
>>> However, the solution should also be able to work with other virtio
>>> backends.
>>> In that case, it may not be possible to rely on the resource table.
>>>
>>
>> Another concern is, do we need the size of the structure in the
>> first-place even to retrieve the 'size' field from the structure or
>> verify the integrity of the structure?
>>
>> For example:
>> https://github.com/torvalds/linux/blob/27fa82620cbaa89a7fc11ac3057701d598813e87/drivers/remoteproc/remoteproc_virtio.c#L301
>>
>>
>> Here to verify the integrity of the resource table, we are using virtio
>> config space size.
>>
>> If we do then it's better to provide the 'size' field some other way
>> before parsing of the rpmsg config space in any virtio backend. Like in
>> the remoteproc virtio backend it's provided via the resource table.
>>
>> Let me know if I am overthinking :-) and we want the 'size' field in the
>> config space. I am just trying to make it as minimal as possible.
>
> I think it is better to have a 'size' field in the structure.
>
Ack. I will work on new revision as per our conversation here, and send v3.
Thanks.
>>
>> Thanks,
>> Tanmay
>>
>>> Regards,
>>> Arnaud
>>>
>>>>
>>>>> 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
>>>>>>>
>>>>>
>>>>
>>>
>>
