On 6/19/2026 2:45 AM, Arnaud POULIQUEN wrote:
>
>
> On 6/18/26 18:31, Shah, Tanmay wrote:
>>
>>
>> On 6/18/2026 3:32 AM, Arnaud POULIQUEN wrote:
>>>
>>>
>>> On 6/17/26 19:41, Shah, Tanmay wrote:
>>>>
>>>>
>>>> On 6/17/2026 4:15 AM, Arnaud POULIQUEN wrote:
>>>>> 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
>>>>>
>>>>
>>>> Ack.
>>>>
>>>>>
>>>>> 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.
>>>>>
>>>>>
>>>>
>>>> This part I don't understand. `rpmsg_buf_align` is alignment for only
>>>> single buffer size. The linux kernel is checking that single rx buf
>>>> size
>>>> and tx buf size is aligned with `rpmsg_buf_align` as firmware has
>>>> claimed.
>>>>
>>>> For reference the openamp-system-reference PR:
>>>> https://github.com/OpenAMP/openamp-system-reference/pull/106/changes
>>>>
>>>> .vdev_config = {
>>>> .version = 1,
>>>> .reserved = 0,
>>>> .size = (uint16_t)(sizeof(struct rpmsg_virtio_config) -
>>>> sizeof(bool)),
>>>> .alignment = RPMSG_BUF_ALIGN,
>>>> .reserved1 = 0,
>>>> /* Tx for host */
>>>> .h2r_buf_size = metal_align_up(4096, RPMSG_BUF_ALIGN),
>>>> /* Rx for host */
>>>> .r2h_buf_size = metal_align_up(4096, RPMSG_BUF_ALIGN),
>>>> },
>>>>
>>>> IIUC, The linux kernel is not really supposed to modify
>>>> `rpmsg_buf_align`. It only uses it to check that firmware has assigned
>>>> correct size of single rx and tx buffer.
>>>>
>>>>
>>>> When the linux kernel uses dma_alloc_coherent() API it aligns total
>>>> buffer size with page size. That is different than single tx buf size
>>>> and single rx buf size. The total buf size alignment to page size is
>>>> irrelevant to `rpmsg_buf_align` field.
>>>>
>>>> Please let me know if I am missing something or didn't understand your
>>>> comment. I prefer that `rpmsg_buf_align` should be only modified by the
>>>> firmware and not the linux kernel.
>>>
>>>
>>> Sorry it was unclear, let try to reexplain my suggestion:
>>>
>>> Two alignment constraints can apply:
>>> - The remote processor can require an alignment through
>>> vdev_config::alignment.
>>> - The main processor, which runs Linux or another operating system (OS),
>>> can require a different alignment, for example, for cache alignment.
>>> In current Linux implementation no constraint in Linux.
>>> nevertheless I would be in favor of taking into account such future
>>> constraint without imposing constraint on the buffer sizes.
>>
>> Is this ever going to be ture? Is it ever possible that Linux and remote
>> has different cache alignment? IIUC, both will be using same cache and
>> so same alignment will be applicable. That is why only signle alignment
>> is required.
>
> Some remote processors, for example, some Arm Cortex-M33, do not
> integrate cache. Even if cache exists, cache can be enabled on one
> processor, but not on the other.
>
Okay, how about introducing two alignment in that case?
vdev_config::rpmsg_buf_align_remote, and vdev_config::rpmsg_buf_align_host ?
If remote doesn't have cache, then remote alignment will be 0, and the
*_host alignment can be applied. The rsc_table can provide both, and the
*_host will take priority over *_remote.
>>
>>> Based on that in short term the local 'rpmsg_buf_align' would still
>>> computed
>>> only from vdev_config::alignment (not update of vdev_config::alignment).
>>>
>>> virtio_cread(vdev, struct virtio_rpmsg_config,
>>> rpmsg_buf_align, &rpmsg_buf_align);
>>>
>>> Then you could use use ALIGN() helper:
>>>
>>> unsigned int rx_buf_align_size = ALIGN(vrp->rx_buf_size,
>>> rpmsg_buf_align);
>>> unsigned int tx_buf_align_size = ALIGN(vrp->tx_buf_size,
>>> rpmsg_buf_align);
>>>
>>
>> This is where I have different opinion. Instead of Linux using ALIGN()
>> macro, can we expect that firmware must assign the aligned buffer size
>> with vdev_config::rpmsg_buf_align? And so Linux will fail if the buffer
>> size is not aligned already from the firmware side. That is why I had
>> introduced checks instead of doing alignment by linux.
>>
>>> total_buf_space = (vrp->num_rx_buf * rx_buf_align_size) +
>>> (vrp->num_tx_buf * tx_buf_align_size);
>>>
>>> vrp->tx_bufs = bufs_va + vrp->num_rx_buf * rx_buf_align_size;
>>>
>>> Apply the same rule to cpu_addr in the vring descriptor:
>>>
>>> void *cpu_addr = vrp->rx_bufs + i * rx_buf_align_size;
>>>
>>> rpmsg_sg_init(&sg, cpu_addr, vrp->rx_buf_size);
>>>
>>> With this approach, the buffer addresses remain aligned
>>> independently of vdev_config::Rxbuf_size and vdev_config::txbuf_size.
>>> Don't hesitate if it is still not clear!
>>
>> How they remain aligned independent of tx/rx_buf_size? tx_bufs address
>> is still calculated based on rx_buf_align_size, so its alignment still
>> depends on rx_buf_align_size which is derived using
>> vdev_config::rpmsg_buf_align.>
>> I think we are trying to achive the same thing, but implementation is
>> differnt. We just need to decide where the alignment should be done?
>>
>> Either on the linux side? Or in the firmware resource table?
>>
>> I prefer that the firmware should already provide aligned buffer size,
>> and Linux should only check it. If alignment is not done, then simply
>> fail with error. That way, firmware also knows the correct size of the
>> buffer. If Linux does the alignment, then the firmware is not aware of
>> the correct size that is used by the linux.
>>
>> I am open to move the alignment operation to the linux side with the
>> reasonable justification.
>
> That remains a suggestion. My main concern with the implementation is
> that RPMsg size should depend only on the max playlod size needed, not
> also on the memory alignment.
Okay, I think this is a good reason to apply alignment on the linux
side. If I understand correctly, the rpmsg buffer size will be used as
it is from the rsc table, but vdev_config::alignment will be used only
to decide the start address of the next buffer. If that is the
intention, then I agree, and I will refactor the patch accordingly.
>
> If this constraint is kept, it must be imposed on all other non-Linux
> solutions. Otherwise, the remote implementation depends on the main
> processor implementation.
>
> From my POV, It would be preferable not to impose such constraint when
> possible.
>
Okay.
> Thanks,
> Arnaud
>
>>
>> Thank You,
>> Tanmay
>>
>>>>
>>>>
>>>>>> + 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;
>>>>> +
>>>>>
>>>>
>>>> I am okay with the above proposal with minor difference:
>>>>
>>>> My proposal:
>>>>
>>>> +struct virtio_rpmsg_config {
>>>> + u8 version;
>>>> + __virtio16 size;
>>>> + __virtio16 rpmsg_buf_align;
>>>> + /* The tx/rx individual buffer size (if VIRTIO_RPMSG_F_BUFSZ) */
>>>> + __virtio32 txbuf_size;
>>>> + __virtio32 rxbuf_size;
>>>> +} __packed;
>>>>
>>>> I just want to keep version field 8-bit, as we will probably never use
>>>> upper byte of that field if we use 16-bit. Rest is okay. If the
>>>> strucutre is packed then reserved bytes are not needed.
>>>>
>>>> Please let me know your view.
>>>
>>> No strong opinion on that. In the end, this structure is read only one
>>> time.
>>> If it is acceptable to Mathieu, it is acceptable to me.
>>>
>>> Thanks,
>>> Arnaud
>>>
>>>>
>>>> Thanks,
>>>> Tanmay
>>>>
>>>>
>>>>> Regards,
>>>>> Arnaud
>>>>>
>>>>>> +
>>>>>> +#endif /* _LINUX_VIRTIO_RPMSG_H */
>>>>>
>>>>
>>>
>>
>
