Date:   Thu, 2 Dec 2021 20:32:31 -0600
From:   Bjorn Andersson <bjorn.andersson@linaro.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
Cc:     Ohad Ben-Cohen <ohad@wizery.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-stm32@st-md-mailman.stormreply.com, julien.massot@iot.bzh
Subject: Re: [PATCH v7 09/12] rpmsg: char: Add possibility to use default
 endpoint of the rpmsg device.
Message-ID: <YamBv4Sy3Jtdp7Wu@builder.lan>
References: <20211108141937.13016-1-arnaud.pouliquen@foss.st.com>
 <20211108141937.13016-10-arnaud.pouliquen@foss.st.com>
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On Mon 08 Nov 08:19 CST 2021, Arnaud Pouliquen wrote:

> Current implementation create/destroy a new endpoint on each
> rpmsg_eptdev_open/rpmsg_eptdev_release calls.
> 
> For a rpmsg device created by the NS announcement mechanism we need to
> use a unique static endpoint that is the default rpmsg device endpoint
> associated to the channel.
> 
> This patch prepares the introduction of a rpmsg channel device for the
> char device. The rpmsg channel device will require a default endpoint to
> communicate to the remote processor.
> 
> Add the default_ept field in rpmsg_eptdev structure.This pointer
> determines the behavior on rpmsg_eptdev_open and rpmsg_eptdev_release call.
> 
> - If default_ept == NULL:
>   Use the legacy behavior by creating a new endpoint each time
>   rpmsg_eptdev_open is called and release it when rpmsg_eptdev_release
>   is called on /dev/rpmsgX device open/close.
> 
> - If default_ept is set:
>   use the rpmsg device default endpoint for the communication.
> 
> Address the update of _rpmsg_chrdev_eptdev_create in a separate patch for readability.
> 
> Add protection in rpmsg_eptdev_ioctl to prevent to destroy a default endpoint.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
> ---
>  drivers/rpmsg/rpmsg_char.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/rpmsg/rpmsg_char.c b/drivers/rpmsg/rpmsg_char.c
> index 3daf62df69a0..6a01e8e1c111 100644
> --- a/drivers/rpmsg/rpmsg_char.c
> +++ b/drivers/rpmsg/rpmsg_char.c
> @@ -47,6 +47,8 @@ static DEFINE_IDA(rpmsg_minor_ida);
>   * @queue_lock:	synchronization of @queue operations
>   * @queue:	incoming message queue
>   * @readq:	wait object for incoming queue
> + * @default_ept: set to channel default endpoint if the default endpoint should be re-used
> + *              on device open to prevent endpoint address update.
>   */
>  struct rpmsg_eptdev {
>  	struct device dev;
> @@ -57,10 +59,12 @@ struct rpmsg_eptdev {
>  
>  	struct mutex ept_lock;
>  	struct rpmsg_endpoint *ept;
> +	struct rpmsg_endpoint *default_ept;
>  
>  	spinlock_t queue_lock;
>  	struct sk_buff_head queue;
>  	wait_queue_head_t readq;
> +
>  };
>  
>  int rpmsg_chrdev_eptdev_destroy(struct device *dev, void *data)
> @@ -118,7 +122,15 @@ static int rpmsg_eptdev_open(struct inode *inode, struct file *filp)
>  
>  	get_device(dev);
>  
> -	ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
> +	/*
> +	 * If the default_ept is set to true, the rpmsg device default endpoint is used.

default_ept will no longer be "set to true".

Regards,
Bjorn

> +	 * Else a new endpoint is created on open that will be destroyed on release.
> +	 */
> +	if (eptdev->default_ept)
> +		ept = eptdev->default_ept;
> +	else
> +		ept = rpmsg_create_ept(rpdev, rpmsg_ept_cb, eptdev, eptdev->chinfo);
> +
>  	if (!ept) {
>  		dev_err(dev, "failed to open %s\n", eptdev->chinfo.name);
>  		put_device(dev);
> @@ -139,7 +151,8 @@ static int rpmsg_eptdev_release(struct inode *inode, struct file *filp)
>  	/* Close the endpoint, if it's not already destroyed by the parent */
>  	mutex_lock(&eptdev->ept_lock);
>  	if (eptdev->ept) {
> -		rpmsg_destroy_ept(eptdev->ept);
> +		if (!eptdev->default_ept)
> +			rpmsg_destroy_ept(eptdev->ept);
>  		eptdev->ept = NULL;
>  	}
>  	mutex_unlock(&eptdev->ept_lock);
> @@ -266,6 +279,10 @@ static long rpmsg_eptdev_ioctl(struct file *fp, unsigned int cmd,
>  	if (cmd != RPMSG_DESTROY_EPT_IOCTL)
>  		return -EINVAL;
>  
> +	/* Don't allow to destroy a default endpoint. */
> +	if (eptdev->default_ept)
> +		return -EINVAL;
> +
>  	return rpmsg_chrdev_eptdev_destroy(&eptdev->dev, NULL);
>  }
>  
> -- 
> 2.17.1
>