Re: [PATCH v3 4/4] samples: rpmsg: add MTU size info

["Shah, Tanmay" <tanmays@amd.com>]

On 6/2/2026 3:34 AM, Arnaud POULIQUEN wrote:
> 
> 
> On 5/29/26 18:43, Tanmay Shah wrote:
>> RPMsg MTU size can be variable now and no longer hardcoded to 512 bytes.
>> Add log to the sample driver that prints current MTU size of the rpmsg
>> buffer.
>>
>> Signed-off-by: Tanmay Shah <tanmay.shah@amd.com>
>> ---
>>
>> Changes in v3:
>>    - Check for error when retrieving MTU size
>>    - %s/mtu/MTU/
>>
>>   samples/rpmsg/rpmsg_client_sample.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/samples/rpmsg/rpmsg_client_sample.c b/samples/rpmsg/
>> rpmsg_client_sample.c
>> index ae5081662283..55afa53189af 100644
>> --- a/samples/rpmsg/rpmsg_client_sample.c
>> +++ b/samples/rpmsg/rpmsg_client_sample.c
>> @@ -52,6 +52,7 @@ static int rpmsg_sample_probe(struct rpmsg_device
>> *rpdev)
>>   {
>>       int ret;
>>       struct instance_data *idata;
>> +    ssize_t mtu;
>>         dev_info(&rpdev->dev, "new channel: 0x%x -> 0x%x!\n",
>>                       rpdev->src, rpdev->dst);
>> @@ -62,6 +63,14 @@ static int rpmsg_sample_probe(struct rpmsg_device
>> *rpdev)
>>         dev_set_drvdata(&rpdev->dev, idata);
>>   +    mtu = rpmsg_get_mtu(rpdev->ept);
>> +    if (mtu < 0) {
>> +        dev_warn(&rpdev->dev, "invalid rpmsg MTU size = %ld\n", mtu);
>> +        return mtu;
>> +    }
>> +
>> +    dev_info(&rpdev->dev, "rpmsg MTU size = %ld\n", mtu);
>> +
> 
> Do you really need this commit? rpmsg_send should return an error if the
> buffer size is insufficient [1].
> 
> [1] https://elixir.bootlin.com/linux/v7.0.10/source/drivers/rpmsg/
> virtio_rpmsg_bus.c#L517
> 

Here, I just want to demonstrate rpmsg_get_mtu() API. Now we can have a
configurable size of the RPMsg buffer. So rpmsg_get_mtu() API can be
used to check correct buffer length before even using rpmsg_send() API.

I think I should check msg length against mtu size as well.


> Regards,
> Arnaud
> 
>>       /* send a message to our remote processor */
>>       ret = rpmsg_send(rpdev->ept, MSG, strlen(MSG));
>>       if (ret) {
>