linux-kernel - Re: [PATCH v6 06/10] rpmsg: Introduce rpmsg_create_default

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Date:   Mon, 1 Nov 2021 12:37:18 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
Cc:     Ohad Ben-Cohen <ohad@...ery.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        linux-remoteproc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com, julien.massot@....bzh
Subject: Re: [PATCH v6 06/10] rpmsg: Introduce rpmsg_create_default_ept
 function

On Fri 22 Oct 07:54 CDT 2021, Arnaud Pouliquen wrote:

> By providing a callback in the rpmsg_driver structure, the rpmsg devices
> can be probed with a default endpoint created.
> 
> In this case, it is not possible to associated to this endpoint private data
> that could allow the driver to retrieve the context.
> 
> This helper function allows rpmsg drivers to create a default endpoint
> on runtime with an associated private context.
> 
> For example, a driver might create a context structure on the probe and
> want to provide that context as private data for the default rpmsg
> callback.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@...s.st.com>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> Tested-by: Julien Massot <julien.massot@....bzh>
> ---
>  drivers/rpmsg/rpmsg_core.c | 51 ++++++++++++++++++++++++++++++++++++++
>  include/linux/rpmsg.h      | 13 ++++++++++
>  2 files changed, 64 insertions(+)
> 
> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> index 53162038254d..92557c49d460 100644
> --- a/drivers/rpmsg/rpmsg_core.c
> +++ b/drivers/rpmsg/rpmsg_core.c
> @@ -132,6 +132,57 @@ void rpmsg_destroy_ept(struct rpmsg_endpoint *ept)
>  }
>  EXPORT_SYMBOL(rpmsg_destroy_ept);
>  
> +/**
> + * rpmsg_create_default_ept() - create a default rpmsg_endpoint for a rpmsg device
> + * @rpdev: rpmsg channel device
> + * @cb: rx callback handler
> + * @priv: private data for the driver's use
> + * @chinfo: channel_info with the local rpmsg address to bind with @cb
> + *
> + * On register_rpmsg_driver if no callback is provided in the rpmsg_driver structure,
> + * no endpoint is created when the device is probed by the rpmsg bus.
> + *
> + * This function returns a pointer to the default endpoint if already created or creates
> + * an endpoint and assign it as the default endpoint of the rpmsg device.

But if the driver didn't specify a callback, when would this ever
happen?

> + *
> + * Drivers should provide their @rpdev channel (so the new endpoint would belong
> + * to the same remote processor their channel belongs to), an rx callback
> + * function, an optional private data (which is provided back when the
> + * rx callback is invoked), and an address they want to bind with the
> + * callback. If @addr is RPMSG_ADDR_ANY, then rpmsg_create_ept will
> + * dynamically assign them an available rpmsg address (drivers should have
> + * a very good reason why not to always use RPMSG_ADDR_ANY here).
> + *
> + * Returns a pointer to the endpoint on success, or NULL on error.

Correct kerneldoc is "Return: ..."

> + */
> +struct rpmsg_endpoint *rpmsg_create_default_ept(struct rpmsg_device *rpdev,
> +						rpmsg_rx_cb_t cb, void *priv,
> +						struct rpmsg_channel_info chinfo)
> +{
> +	struct rpmsg_endpoint *ept;
> +
> +	if (WARN_ON(!rpdev))
> +		return NULL;
> +
> +	/* It does not make sense to create a default endpoint without a callback. */
> +	if (!cb)
> +		return NULL;
> +
> +	if (rpdev->ept)
> +		return rpdev->ept;

How does the caller know if they should call rpmsg_destroy_ept() on the
returned ept or not?

> +
> +	ept = rpdev->ops->create_ept(rpdev, cb, priv, chinfo);
> +	if (!ept)
> +		return NULL;
> +
> +	/* Assign the new endpoint as default endpoint */
> +	rpdev->ept = ept;
> +	rpdev->src = ept->addr;
> +
> +	return ept;
> +}
> +EXPORT_SYMBOL(rpmsg_create_default_ept);
> +
>  /**
>   * rpmsg_send() - send a message across to the remote processor
>   * @ept: the rpmsg endpoint
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 6fe51549d931..b071ac17ff78 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -172,6 +172,9 @@ void rpmsg_destroy_ept(struct rpmsg_endpoint *);
>  struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_device *,
>  					rpmsg_rx_cb_t cb, void *priv,
>  					struct rpmsg_channel_info chinfo);
> +struct rpmsg_endpoint *rpmsg_create_default_ept(struct rpmsg_device *rpdev,

Is there ever a case where someone outside drivers/rpmsg/ should call
this function?

Regards,
Bjorn

> +						rpmsg_rx_cb_t cb, void *priv,
> +						struct rpmsg_channel_info chinfo);
>  
>  int rpmsg_send(struct rpmsg_endpoint *ept, void *data, int len);
>  int rpmsg_sendto(struct rpmsg_endpoint *ept, void *data, int len, u32 dst);
> @@ -236,6 +239,16 @@ static inline struct rpmsg_endpoint *rpmsg_create_ept(struct rpmsg_device *rpdev
>  	return NULL;
>  }
>  
> +static inline struct rpmsg_endpoint *rpmsg_create_default_ept(struct rpmsg_device *rpdev,
> +							      rpmsg_rx_cb_t cb, void *priv,
> +							      struct rpmsg_channel_info chinfo)
> +{
> +	/* This shouldn't be possible */
> +	WARN_ON(1);
> +
> +	return NULL;
> +}
> +
>  static inline int rpmsg_send(struct rpmsg_endpoint *ept, void *data, int len)
>  {
>  	/* This shouldn't be possible */
> -- 
> 2.17.1
>