Re: [PATCH V7 1/3] rpmsg: core: Add signal API support

[Arnaud POULIQUEN <arnaud.pouliquen@foss.st.com>]

Hello,

On 4/22/23 12:42, Sarannya S wrote:
> From: Deepak Kumar Singh <quic_deesin@quicinc.com>
> 
> Some transports like Glink support the state notifications between
> clients using flow control signals similar to serial protocol signals.
> Local glink client drivers can send and receive flow control status
> to glink clients running on remote processors.
> 
> Add APIs to support sending and receiving of flow control status by
> rpmsg clients.
> 
> Signed-off-by: Deepak Kumar Singh <quic_deesin@quicinc.com>
> Signed-off-by: Sarannya S <quic_sarannya@quicinc.com>
> ---
>  drivers/rpmsg/rpmsg_core.c     | 21 +++++++++++++++++++++
>  drivers/rpmsg/rpmsg_internal.h |  2 ++
>  include/linux/rpmsg.h          | 15 +++++++++++++++
>  3 files changed, 38 insertions(+)
> 
> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> index a2207c0..e8bbe05 100644
> --- a/drivers/rpmsg/rpmsg_core.c
> +++ b/drivers/rpmsg/rpmsg_core.c
> @@ -331,6 +331,25 @@ int rpmsg_trysend_offchannel(struct rpmsg_endpoint *ept, u32 src, u32 dst,
>  EXPORT_SYMBOL(rpmsg_trysend_offchannel);
>  
>  /**
> + * rpmsg_set_flow_control() - sets/clears serial flow control signals
> + * @ept:	the rpmsg endpoint
> + * @enable:	pause/resume incoming data flow	
> + * @dst:	destination address of the endpoint
> + *
> + * Return: 0 on success and an appropriate error value on failure.
> + */
> +int rpmsg_set_flow_control(struct rpmsg_endpoint *ept, bool enable, u32 dst)
> +{
> +	if (WARN_ON(!ept))
> +		return -EINVAL;
> +	if (!ept->ops->set_flow_control)
> +		return -ENXIO;

Here we return an error if the backend does not implement the ops.
But the set_flow_control ops is optional.
Should we return 0 instead with a debug message?

> +
> +	return ept->ops->set_flow_control(ept, enable, dst);
> +}
> +EXPORT_SYMBOL_GPL(rpmsg_set_flow_control);
> +
> +/**
>   * rpmsg_get_mtu() - get maximum transmission buffer size for sending message.
>   * @ept: the rpmsg endpoint
>   *
> @@ -539,6 +558,8 @@ static int rpmsg_dev_probe(struct device *dev)
>  
>  		rpdev->ept = ept;
>  		rpdev->src = ept->addr;
> +
> +		ept->flow_cb = rpdrv->flowcontrol;
>  	}
>  
>  	err = rpdrv->probe(rpdev);
> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
> index 39b646d..b6efd3e 100644
> --- a/drivers/rpmsg/rpmsg_internal.h
> +++ b/drivers/rpmsg/rpmsg_internal.h
> @@ -55,6 +55,7 @@ struct rpmsg_device_ops {
>   * @trysendto:		see @rpmsg_trysendto(), optional
>   * @trysend_offchannel:	see @rpmsg_trysend_offchannel(), optional
>   * @poll:		see @rpmsg_poll(), optional
> + * @set_flow_control:	see @rpmsg_set_flow_control(), optional
>   * @get_mtu:		see @rpmsg_get_mtu(), optional
>   *
>   * Indirection table for the operations that a rpmsg backend should implement.
> @@ -75,6 +76,7 @@ struct rpmsg_endpoint_ops {
>  			     void *data, int len);
>  	__poll_t (*poll)(struct rpmsg_endpoint *ept, struct file *filp,
>  			     poll_table *wait);
> +	int (*set_flow_control)(struct rpmsg_endpoint *ept, bool enable, u32 dst);
>  	ssize_t (*get_mtu)(struct rpmsg_endpoint *ept);
>  };
>  
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 523c98b..a0e9d38 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -64,12 +64,14 @@ struct rpmsg_device {
>  };
>  
>  typedef int (*rpmsg_rx_cb_t)(struct rpmsg_device *, void *, int, void *, u32);
> +typedef int (*rpmsg_flowcontrol_cb_t)(struct rpmsg_device *, void *, bool);
>  
>  /**
>   * struct rpmsg_endpoint - binds a local rpmsg address to its user
>   * @rpdev: rpmsg channel device
>   * @refcount: when this drops to zero, the ept is deallocated
>   * @cb: rx callback handler
> + * @flow_cb: remote flow control callback handler
>   * @cb_lock: must be taken before accessing/changing @cb
>   * @addr: local rpmsg address
>   * @priv: private data for the driver's use
> @@ -92,6 +94,7 @@ struct rpmsg_endpoint {
>  	struct rpmsg_device *rpdev;
>  	struct kref refcount;
>  	rpmsg_rx_cb_t cb;
> +	rpmsg_flowcontrol_cb_t flow_cb;
>  	struct mutex cb_lock;
>  	u32 addr;
>  	void *priv;
> @@ -106,6 +109,7 @@ struct rpmsg_endpoint {
>   * @probe: invoked when a matching rpmsg channel (i.e. device) is found
>   * @remove: invoked when the rpmsg channel is removed
>   * @callback: invoked when an inbound message is received on the channel
> + * @flowcontrol: invoked when remote side flow control status is received
>   */
>  struct rpmsg_driver {
>  	struct device_driver drv;
> @@ -113,6 +117,7 @@ struct rpmsg_driver {
>  	int (*probe)(struct rpmsg_device *dev);
>  	void (*remove)(struct rpmsg_device *dev);
>  	int (*callback)(struct rpmsg_device *, void *, int, void *, u32);
> +	int (*flowcontrol)(struct rpmsg_device *, void *, bool);

I wonder here if we should also add a parameter for the remote source address.
This parameter is already exist for the
int (*callback)(struct rpmsg_device *, void *, int, void *, u32)
useful in case of point to multi point communication...

Regards,
Arnaud

>  };
>  
>  static inline u16 rpmsg16_to_cpu(struct rpmsg_device *rpdev, __rpmsg16 val)
> @@ -192,6 +197,8 @@ __poll_t rpmsg_poll(struct rpmsg_endpoint *ept, struct file *filp,
>  
>  ssize_t rpmsg_get_mtu(struct rpmsg_endpoint *ept);
>  
> +int rpmsg_set_flow_control(struct rpmsg_endpoint *ept, bool enable, u32 dst);
> +
>  #else
>  
>  static inline int rpmsg_register_device_override(struct rpmsg_device *rpdev,
> @@ -316,6 +323,14 @@ static inline ssize_t rpmsg_get_mtu(struct rpmsg_endpoint *ept)
>  	return -ENXIO;
>  }
>  
> +static inline int rpmsg_set_flow_control(struct rpmsg_endpoint *ept, bool enable, u32 dst)
> +{
> +	/* This shouldn't be possible */
> +	WARN_ON(1);
> +
> +	return -ENXIO;
> +}
> +
>  #endif /* IS_ENABLED(CONFIG_RPMSG) */
>  
>  /* use a macro to avoid include chaining to get THIS_MODULE */