Re: [RFC PATCH 1/2] rpmsg: virtio_rpmsg_bus: allow the different vring size for send/recv

[Tanmay Shah <tanmay.shah@amd.com>]

On 11/21/25 3:40 AM, Arnaud POULIQUEN wrote:
> Hi Tanmay,
> 
> On 11/14/25 19:46, Tanmay Shah wrote:
>> From: Xiang Xiao <xiaoxiang781216@gmail.com>
>>
>> it's useful if the communication throughput is different from each side
>>
>> Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
>> Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
> 
> 
> Thanks you for reopening of this series!
>> ---
>>   drivers/rpmsg/virtio_rpmsg_bus.c | 47 ++++++++++++++++----------------
>>   1 file changed, 24 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/ 
>> virtio_rpmsg_bus.c
>> index 484890b4a6a7..cc26dfcc3e29 100644
>> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
>> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
>> @@ -37,8 +37,9 @@
>>    * @svq:    tx virtqueue
>>    * @rbufs:    kernel address of rx buffers
>>    * @sbufs:    kernel address of tx buffers
>> - * @num_bufs:    total number of buffers for rx and tx
>> - * @buf_size:   size of one rx or tx buffer
>> + * @num_rbufs:    total number of buffers for rx
>> + * @num_sbufs:    total number of buffers for tx
> 
> Nitpicking... I wonder if rx, tx term would be more generic
> In such case s/num_rxbufs/n_rx_buf/ s/num_sbufs/num_txbufs/
> 

Ack. I can change that.

> Regards
> Arnaud
> 
>> + * @buf_size:    size of one rx or 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.
>> @@ -57,7 +58,8 @@ struct virtproc_info {
>>       struct virtio_device *vdev;
>>       struct virtqueue *rvq, *svq;
>>       void *rbufs, *sbufs;
>> -    unsigned int num_bufs;
>> +    unsigned int num_rbufs;
>> +    unsigned int num_sbufs;
>>       unsigned int buf_size;
>>       int last_sbuf;
>>       dma_addr_t bufs_dma;
>> @@ -112,7 +114,7 @@ struct virtio_rpmsg_channel {
>>   /*
>>    * We're allocating buffers of 512 bytes each for communications. The
>>    * number of buffers will be computed from the number of buffers 
>> supported
>> - * by the vring, upto a maximum of 512 buffers (256 in each direction).
>> + * by the vring, up to a maximum of 256 in each direction.
>>    *
>>    * Each buffer will have 16 bytes for the msg header and 496 bytes for
>>    * the payload.
>> @@ -127,7 +129,7 @@ struct virtio_rpmsg_channel {
>>    * can change this without changing anything in the firmware of the 
>> remote
>>    * processor.
>>    */
>> -#define MAX_RPMSG_NUM_BUFS    (512)
>> +#define MAX_RPMSG_NUM_BUFS    (256)
>>   #define MAX_RPMSG_BUF_SIZE    (512)
>>   /*
>> @@ -439,11 +441,8 @@ static void *get_a_tx_buf(struct virtproc_info *vrp)
>>       /* support multiple concurrent senders */
>>       mutex_lock(&vrp->tx_lock);
>> -    /*
>> -     * either pick the next unused tx buffer
>> -     * (half of our buffers are used for sending messages)
>> -     */
>> -    if (vrp->last_sbuf < vrp->num_bufs / 2)
>> +    /* either pick the next unused tx buffer */
>> +    if (vrp->last_sbuf < vrp->num_sbufs)
>>           ret = vrp->sbufs + vrp->buf_size * vrp->last_sbuf++;
>>       /* or recycle a used one */
>>       else
>> @@ -878,19 +877,20 @@ static int rpmsg_probe(struct virtio_device *vdev)
>>       vrp->rvq = vqs[0];
>>       vrp->svq = vqs[1];
>> -    /* we expect symmetric tx/rx vrings */
>> -    WARN_ON(virtqueue_get_vring_size(vrp->rvq) !=
>> -        virtqueue_get_vring_size(vrp->svq));
>> -
>>       /* we need less buffers if vrings are small */
>> -    if (virtqueue_get_vring_size(vrp->rvq) < MAX_RPMSG_NUM_BUFS / 2)
>> -        vrp->num_bufs = virtqueue_get_vring_size(vrp->rvq) * 2;
>> +    if (virtqueue_get_vring_size(vrp->rvq) < MAX_RPMSG_NUM_BUFS)
>> +        vrp->num_rbufs = virtqueue_get_vring_size(vrp->rvq);
>> +    else
>> +        vrp->num_rbufs = MAX_RPMSG_NUM_BUFS;
>> +
>> +    if (virtqueue_get_vring_size(vrp->svq) < MAX_RPMSG_NUM_BUFS)
>> +        vrp->num_sbufs = virtqueue_get_vring_size(vrp->svq);
>>       else
>> -        vrp->num_bufs = MAX_RPMSG_NUM_BUFS;
>> +        vrp->num_sbufs = MAX_RPMSG_NUM_BUFS;
>>       vrp->buf_size = MAX_RPMSG_BUF_SIZE;
>> -    total_buf_space = vrp->num_bufs * vrp->buf_size;
>> +    total_buf_space = (vrp->num_rbufs + vrp->num_sbufs) * vrp->buf_size;
>>       /* allocate coherent memory for the buffers */
>>       bufs_va = dma_alloc_coherent(vdev->dev.parent,
>> @@ -904,14 +904,14 @@ static int rpmsg_probe(struct virtio_device *vdev)
>>       dev_dbg(&vdev->dev, "buffers: va %p, dma %pad\n",
>>           bufs_va, &vrp->bufs_dma);
>> -    /* half of the buffers is dedicated for RX */
>> +    /* first part of the buffers is dedicated for RX */
>>       vrp->rbufs = bufs_va;
>> -    /* and half is dedicated for TX */
>> -    vrp->sbufs = bufs_va + total_buf_space / 2;
>> +    /* and second part is dedicated for TX */
>> +    vrp->sbufs = bufs_va + vrp->num_rbufs * vrp->buf_size;
>>       /* set up the receive buffers */
>> -    for (i = 0; i < vrp->num_bufs / 2; i++) {
>> +    for (i = 0; i < vrp->num_rbufs; i++) {
>>           struct scatterlist sg;
>>           void *cpu_addr = vrp->rbufs + i * vrp->buf_size;
>> @@ -1001,7 +1001,8 @@ static int rpmsg_remove_device(struct device 
>> *dev, void *data)
>>   static void rpmsg_remove(struct virtio_device *vdev)
>>   {
>>       struct virtproc_info *vrp = vdev->priv;
>> -    size_t total_buf_space = vrp->num_bufs * vrp->buf_size;
>> +    unsigned int num_bufs = vrp->num_rbufs + vrp->num_sbufs;
>> +    size_t total_buf_space = num_bufs * vrp->buf_size;
>>       int ret;
>>       virtio_reset_device(vdev);
>