linux-kernel - Re: [PATCH] rpmsg: virtio: set dst address on first message received

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Date:   Fri, 6 May 2022 11:12:22 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH] rpmsg: virtio: set dst address on first message received

On Tue, Mar 15, 2022 at 04:38:56PM +0100, Arnaud Pouliquen wrote:
> when a rpmsg channel has been locally created with a destination address

s/when/Wen

Also, please be more specific about the "locally created" part, i.e
rpmsg_ctrldev_ioctl() -> rpmsg_create_channel().  Otherwise it is really hard to
understand the context of this change.

> set to RPMSG_ADDR_ANY, a name service announcement message is sent to
> the remote side. Then the destination address is never updated, making it
> impossible to send messages to the remote.
> 
> An example of kernel trace observed:
> rpmsg_tty virtio0.rpmsg-tty.29.-1: invalid addr (src 0x1d, dst 0xffffffff)
> 
> Implement same strategy than the open-amp library:
> On the reception of the first message, if the destination address is
> RPMSG_ADDR_ANY, then set it to address of the remote endpoint that
> send the message.
>

I would have expected a "Fixes:" tag.

> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
> 
> ---
> Remark:
> An alternative (or a complement?) could be to add a NS bind/unbind in
> the NS announcement channel (in rpmsg_ns.c).
> This would allow the local and/or the remote processor to inform the
> remote side the the service announced in bound.
> ---
>  drivers/rpmsg/virtio_rpmsg_bus.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 3ede25b1f2e4..99d2119cc164 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -708,6 +708,7 @@ static ssize_t virtio_rpmsg_get_mtu(struct rpmsg_endpoint *ept)
>  static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
>  			     struct rpmsg_hdr *msg, unsigned int len)
>  {
> +	struct rpmsg_device *rpdev;
>  	struct rpmsg_endpoint *ept;
>  	struct scatterlist sg;
>  	bool little_endian = virtio_is_little_endian(vrp->vdev);
> @@ -746,6 +747,15 @@ static int rpmsg_recv_single(struct virtproc_info *vrp, struct device *dev,
>  	mutex_unlock(&vrp->endpoints_lock);
>  
>  	if (ept) {
> +		rpdev = ept->rpdev;
> +		if (rpdev->ept == ept && rpdev->dst == RPMSG_ADDR_ANY) {

Please add a comment to explain the first part of the if() clause.  It took me
quite some time to understand. 

> +			/*
> +			 * First message received from the remote side on the default endpoint,
> +			 * update channel destination address.
> +			 */
> +			rpdev->dst = msg->src;

This triggers a bot warning and should be addressed.  If it can't be addressed add
a comment that clearly explains why so that we don't end up receiving patches
for it every 4 weeks.

Thanks,
Mathieu

> +		}
> +
>  		/* make sure ept->cb doesn't go away while we use it */
>  		mutex_lock(&ept->cb_lock);
>  
> -- 
> 2.25.1
>