Re: [PATCH v2 03/14] serial: port: Introduce a common helper to read properties

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, Feb 26, 2024 at 04:19:19PM +0200, Andy Shevchenko wrote:
> Several serial drivers want to read the same or similar set of
> the port properties. Make a common helper for them.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
>  drivers/tty/serial/serial_port.c | 134 +++++++++++++++++++++++++++++++
>  include/linux/serial_core.h      |   1 +
>  2 files changed, 135 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c
> index 88975a4df306..ecc980e9dba6 100644
> --- a/drivers/tty/serial/serial_port.c
> +++ b/drivers/tty/serial/serial_port.c
> @@ -8,7 +8,10 @@
>  
>  #include <linux/device.h>
>  #include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
>  #include <linux/pm_runtime.h>
> +#include <linux/property.h>
>  #include <linux/serial_core.h>
>  #include <linux/spinlock.h>
>  
> @@ -82,6 +85,137 @@ void uart_remove_one_port(struct uart_driver *drv, struct uart_port *port)
>  }
>  EXPORT_SYMBOL(uart_remove_one_port);
>  
> +/**
> + * uart_read_port_properties - read firmware properties of the given UART port

I like, but:

> + * @port: corresponding port
> + * @use_defaults: apply defaults (when %true) or validate the values (when %false)

Using random booleans in a function is horrid.  Every time you see the
function call, or want to call it, you need to go and look up what the
boolean is and means.

Make 2 public functions here, one that does it with use_defaults=true
and one =false and then have them both call this one static function,
that way the function names themselves are easy to read and understand
and maintain over time.

thanks,

greg k-h


> + *
> + * The following device properties are supported:
> + *   - clock-frequency (optional)
> + *   - fifo-size (optional)
> + *   - no-loopback-test (optional)
> + *   - reg-shift (defaults may apply)
> + *   - reg-offset (value may be validated)
> + *   - reg-io-width (defaults may apply or value may be validated)
> + *   - interrupts (OF only)
> + *   - serial [alias ID] (OF only)
> + *
> + * If the port->dev is of struct platform_device type the interrupt line
> + * will be retrieved via platform_get_irq() call against that device.
> + * Otherwise it will be assigned by fwnode_irq_get() call. In both cases
> + * the index 0 of the resource is used.
> + *
> + * The caller is responsible to initialize the following fields of the @port
> + *   ->dev (must be valid)
> + *   ->flags
> + *   ->mapbase
> + *   ->mapsize
> + *   ->regshift (if @use_defaults is false)
> + * before calling this function. Alternatively the above mentioned fields
> + * may be zeroed, in such case the only ones, that have associated properties
> + * found, will be set to the respective values.
> + *
> + * If no error happened, the ->irq, ->mapbase, ->mapsize will be altered.
> + * The ->iotype is always altered.
> + *
> + * When @use_defaults is true and the respective property is not found
> + * the following values will be applied:
> + *   ->regshift = 0
> + * In this case IRQ must be provided, otherwise an error will be returned.
> + *
> + * When @use_defaults is false and the respective property is found
> + * the following values will be validated:
> + *   - reg-io-width (->iotype)
> + *   - reg-offset (->mapsize against ->mapbase)
> + *
> + * Returns: 0 on success or negative errno on failure
> + */
> +int uart_read_port_properties(struct uart_port *port, bool use_defaults)
> +{
> +	struct device *dev = port->dev;
> +	u32 value;
> +	int ret;
> +
> +	/* Read optional UART functional clock frequency */
> +	device_property_read_u32(dev, "clock-frequency", &port->uartclk);
> +
> +	/* Read the registers alignment (default: 8-bit) */
> +	ret = device_property_read_u32(dev, "reg-shift", &value);
> +	if (ret)
> +		port->regshift = use_defaults ? 0 : port->regshift;
> +	else
> +		port->regshift = value;
> +
> +	/* Read the registers I/O access type (default: MMIO 8-bit) */
> +	ret = device_property_read_u32(dev, "reg-io-width", &value);
> +	if (ret) {
> +		port->iotype = UPIO_MEM;
> +	} else {
> +		switch (value) {
> +		case 1:
> +			port->iotype = UPIO_MEM;
> +			break;
> +		case 2:
> +			port->iotype = UPIO_MEM16;
> +			break;
> +		case 4:
> +			port->iotype = device_is_big_endian(dev) ? UPIO_MEM32BE : UPIO_MEM32;
> +			break;
> +		default:
> +			if (!use_defaults) {
> +				dev_err(dev, "Unsupported reg-io-width (%u)\n", value);
> +				return -EINVAL;
> +			}
> +			port->iotype = UPIO_UNKNOWN;
> +			break;
> +		}
> +	}
> +
> +	/* Read the address mapping base offset (default: no offset) */
> +	ret = device_property_read_u32(dev, "reg-offset", &value);
> +	if (ret)
> +		value = 0;
> +
> +	/* Check for shifted address mapping overflow */
> +	if (!use_defaults && port->mapsize < value) {
> +		dev_err(dev, "reg-offset %u exceeds region size %pa\n", value, &port->mapsize);
> +		return -EINVAL;
> +	}
> +
> +	port->mapbase += value;
> +	port->mapsize -= value;
> +
> +	/* Read optional FIFO size */
> +	device_property_read_u32(dev, "fifo-size", &port->fifosize);
> +
> +	if (device_property_read_bool(dev, "no-loopback-test"))
> +		port->flags |= UPF_SKIP_TEST;
> +
> +	/* Get index of serial line, if found in DT aliases */
> +	ret = of_alias_get_id(dev_of_node(dev), "serial");
> +	if (ret >= 0)
> +		port->line = ret;
> +
> +	if (dev_is_platform(dev))
> +		ret = platform_get_irq(to_platform_device(dev), 0);
> +	else
> +		ret = fwnode_irq_get(dev_fwnode(dev), 0);
> +	if (ret == -EPROBE_DEFER)
> +		return ret;
> +	if (ret > 0)
> +		port->irq = ret;
> +	else if (use_defaults)
> +		/* By default IRQ support is mandatory */
> +		return ret;
> +	else
> +		port->irq = 0;
> +
> +	port->flags |= UPF_SHARE_IRQ;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(uart_read_port_properties);

EXPORT_SYMBOL_GPL()?  I have to ask :)

thanks,

greg k-h