Re: [PATCH 2/3] console: Add simplified 'serdev' framework from Linux kernel

[Sascha Hauer <s.hauer@pengutronix.de>]

Hi Andrey,

Some comments inside.


On Mon, Mar 26, 2018 at 06:09:14AM -0700, Andrey Smirnov wrote:
> Port 'serdev' UART-slave deivce framework found in recent Linux
> kernels (post 4.13) in order to be able to port 'serdev' slave drivers
> from Linux.
> 
> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> @@ -323,6 +324,17 @@ int console_register(struct console_device *newcdev)
>  		dev->parent = newcdev->dev;
>  	platform_device_register(dev);
>  
> +	newcdev->open_count = 0;
> +
> +	/*
> +	 * If our console deive is a serdev, we skip the creation of

s/deive/device/

> +	 * corresponding entry in /dev as well as registration in
> +	 * console_list and just go straigh to populating child

s/straigh/straight/

> +	 * devices.
> +	 */
> +	if (serdev_node)
> +		return of_platform_populate(serdev_node, NULL, dev);

How is this going to be used? A serdev driver binds to the serdev_node
and then it probably needs to get a pointer to the console device,
right? How does the driver accomplish this?

> +/**
> + * struct serdev_device - Basic representation of an serdev device
> + *
> + * @dev:		Corresponding device
> + * @fifo:		Circular buffer used for console draining
> + * @buf:		Buffer used to pass Rx data to consumers
> + * @poller		Async poller used to poll this serdev
> + * @polling_interval:	Async poller periodicity
> + * @polling_window:	Duration of a single busy loop poll
> + * @receive_buf:	Function called with data received from device;
> + *			returns number of bytes accepted;
> + */
> +struct serdev_device {
> +	struct device_d *dev;
> +	struct kfifo *fifo;
> +	unsigned char *buf;
> +	struct poller_async poller;
> +	uint64_t polling_interval;
> +	uint64_t polling_window;
> +
> +	int (*receive_buf)(struct serdev_device *, const unsigned char *,
> +			   size_t);
> +};
> +
> +int serdev_device_open(struct serdev_device *);
> +unsigned int serdev_device_set_baudrate(struct serdev_device *, unsigned int);
> +int serdev_device_write(struct serdev_device *, const unsigned char *,
> +			size_t, unsigned long);

So a serdev driver uses serdev_device_write() to send characters out. To
receive characters it has to implement serdev_device->receive_buf,
right? What kind of devices did you implement this for? For devices
which send data without request (GPS?) this seems the way to go. For
others a synchronous receive function might be good, no?

Sascha

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