linux-kernel - Re: [PATCH V2 1/3] rpmsg: core: Add signal API support

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Date:   Fri, 11 Mar 2022 15:11:40 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Deepak Kumar Singh <quic_deesin@...cinc.com>
Cc:     swboyd@...omium.org, quic_clew@...cinc.com,
        mathieu.poirier@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        Ohad Ben-Cohen <ohad@...ery.com>
Subject: Re: [PATCH V2 1/3] rpmsg: core: Add signal API support

On Tue 18 Jan 13:43 CST 2022, Deepak Kumar Singh wrote:

> Some transports like Glink support the state notifications between
> clients using signals similar to serial protocol signals.
> Local glink client drivers can send and receive signals to glink
> clients running on remote processors.
> 
> Add APIs to support sending and receiving of signals by rpmsg clients.
> 
> Signed-off-by: Deepak Kumar Singh <quic_deesin@...cinc.com>
> ---
>  drivers/rpmsg/rpmsg_core.c     | 21 +++++++++++++++++++++
>  drivers/rpmsg/rpmsg_internal.h |  2 ++
>  include/linux/rpmsg.h          | 14 ++++++++++++++
>  3 files changed, 37 insertions(+)
> 
> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> index d3eb600..6712418 100644
> --- a/drivers/rpmsg/rpmsg_core.c
> +++ b/drivers/rpmsg/rpmsg_core.c
> @@ -328,6 +328,24 @@ 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:	enable or disable serial flow control
> + *
> + * Return: 0 on success and an appropriate error value on failure.
> + */
> +int rpmsg_set_flow_control(struct rpmsg_endpoint *ept, bool enable)

This API looks nice and clean and deals with flow control.

> +{
> +	if (WARN_ON(!ept))
> +		return -EINVAL;
> +	if (!ept->ops->set_flow_control)
> +		return -ENXIO;
> +
> +	return ept->ops->set_flow_control(ept, enable);
> +}
> +EXPORT_SYMBOL(rpmsg_set_flow_control);
> +
> +/**
>   * rpmsg_get_mtu() - get maximum transmission buffer size for sending message.
>   * @ept: the rpmsg endpoint
>   *
> @@ -535,6 +553,9 @@ static int rpmsg_dev_probe(struct device *dev)
>  
>  		rpdev->ept = ept;
>  		rpdev->src = ept->addr;
> +
> +		if (rpdrv->signals)
> +			ept->sig_cb = rpdrv->signals;
>  	}
>  
>  	err = rpdrv->probe(rpdev);
> diff --git a/drivers/rpmsg/rpmsg_internal.h b/drivers/rpmsg/rpmsg_internal.h
> index b1245d3..35c2197 100644
> --- a/drivers/rpmsg/rpmsg_internal.h
> +++ b/drivers/rpmsg/rpmsg_internal.h
> @@ -53,6 +53,7 @@ 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.
> @@ -73,6 +74,7 @@ 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);
>  	ssize_t (*get_mtu)(struct rpmsg_endpoint *ept);
>  };
>  
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 02fa911..06d090c 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -62,12 +62,14 @@ struct rpmsg_device {
>  };
>  
>  typedef int (*rpmsg_rx_cb_t)(struct rpmsg_device *, void *, int, void *, u32);
> +typedef int (*rpmsg_rx_sig_t)(struct rpmsg_device *, void *, u32);

This callback however, is still using the original low level tty
signals.

Is there any reason why this can't be "rpmsg_flowcontrol_cb_t" and take
a boolean, so we get a clean interface in both directions?

Regards,
Bjorn

>  
>  /**
>   * 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
> + * @sig_cb: rx serial signal handler
>   * @cb_lock: must be taken before accessing/changing @cb
>   * @addr: local rpmsg address
>   * @priv: private data for the driver's use
> @@ -90,6 +92,7 @@ struct rpmsg_endpoint {
>  	struct rpmsg_device *rpdev;
>  	struct kref refcount;
>  	rpmsg_rx_cb_t cb;
> +	rpmsg_rx_sig_t sig_cb;
>  	struct mutex cb_lock;
>  	u32 addr;
>  	void *priv;
> @@ -111,6 +114,7 @@ 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 (*signals)(struct rpmsg_device *rpdev, void *priv, u32);
>  };
>  
>  static inline u16 rpmsg16_to_cpu(struct rpmsg_device *rpdev, __rpmsg16 val)
> @@ -188,6 +192,8 @@ __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);
> +
>  #else
>  
>  static inline int rpmsg_register_device(struct rpmsg_device *rpdev)
> @@ -306,6 +312,14 @@ 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)
> +{
> +	/* 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 */
> -- 
> 2.7.4
>