Re: [PATCH v3 4/4] tty: serial: 8250: add DFL bus driver for Altera 16550.

[matthew.gerlach@linux.intel.com]

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On Wed, 5 Oct 2022, Ilpo Järvinen wrote:

> On Tue, 4 Oct 2022, matthew.gerlach@linux.intel.com wrote:
>
>> From: Matthew Gerlach <matthew.gerlach@linux.intel.com>
>>
>> Add a Device Feature List (DFL) bus driver for the Altera
>> 16550 implementation of UART.
>>
>> Signed-off-by: Matthew Gerlach <matthew.gerlach@linux.intel.com>
>> Reported-by: kernel test robot <lkp@intel.com>
>> ---
>> v3: use passed in location of registers
>>     use cleaned up functions for parsing parameters
>>
>> v2: clean up error messages
>>     alphabetize header files
>>     fix 'missing prototype' error by making function static
>>     tried to sort Makefile and Kconfig better
>> ---
>>  drivers/tty/serial/8250/8250_dfl.c | 177 +++++++++++++++++++++++++++++
>>  drivers/tty/serial/8250/Kconfig    |   9 ++
>>  drivers/tty/serial/8250/Makefile   |   1 +
>>  3 files changed, 187 insertions(+)
>>  create mode 100644 drivers/tty/serial/8250/8250_dfl.c
>>
>> diff --git a/drivers/tty/serial/8250/8250_dfl.c b/drivers/tty/serial/8250/8250_dfl.c
>> new file mode 100644
>> index 000000000000..110ad3a73459
>> --- /dev/null
>> +++ b/drivers/tty/serial/8250/8250_dfl.c
>> @@ -0,0 +1,177 @@
>
>> +static int dfl_uart_get_params(struct device *dev, void __iomem *dfh_base, resource_size_t max,
>> +			       struct uart_8250_port *uart)
>> +{
>> +	u64 v, fifo_len, reg_width;
>> +	int off;
>> +
>> +	if (!dfhv1_has_params(dfh_base)) {
>> +		dev_err(dev, "missing required DFH parameters\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	off = dfhv1_find_param(dfh_base, max, DFHv1_PARAM_ID_CLK_FRQ);
>> +	if (off < 0) {
>> +		dev_err(dev, "missing CLK_FRQ param\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	uart->port.uartclk = readq(dfh_base + off);
>> +	dev_dbg(dev, "UART_CLK_ID %u Hz\n", uart->port.uartclk);
>> +
>> +	off = dfhv1_find_param(dfh_base, max, DFHv1_PARAM_ID_FIFO_LEN);
>> +	if (off < 0) {
>> +		dev_err(dev, "missing FIFO_LEN param\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	fifo_len = readq(dfh_base + off);
>> +	dev_dbg(dev, "UART_FIFO_ID fifo_len %llu\n", fifo_len);
>> +
>> +	switch (fifo_len) {
>> +	case 32:
>> +		uart->port.type = PORT_ALTR_16550_F32;
>> +		break;
>> +
>> +	case 64:
>> +		uart->port.type = PORT_ALTR_16550_F64;
>> +		break;
>> +
>> +	case 128:
>> +		uart->port.type = PORT_ALTR_16550_F128;
>> +		break;
>> +
>> +	default:
>> +		dev_err(dev, "bad fifo_len %llu\n", fifo_len);
>
> I'd tell user "unsupported" rather than "bad".

The word, unsupported, sounds better.  I will change it in both places you 
suggested.

>
>> +		return -EINVAL;
>> +	}
>> +
>> +	off = dfhv1_find_param(dfh_base, max, DFHv1_PARAM_ID_REG_LAYOUT);
>> +	if (off < 0) {
>> +		dev_err(dev, "missing REG_LAYOUT param\n");
>> +		return -EINVAL;
>> +	}
>> +
>> +	v = readq(dfh_base + off);
>> +	uart->port.regshift = FIELD_GET(DFHv1_PARAM_ID_REG_SHIFT, v);
>> +	reg_width = FIELD_GET(DFHv1_PARAM_ID_REG_WIDTH, v);
>> +
>> +	dev_dbg(dev, "UART_LAYOUT_ID width %lld shift %d\n",
>> +		FIELD_GET(DFHv1_PARAM_ID_REG_WIDTH, v), (int)uart->port.regshift);
>
> Why not use reg_width directly?

Good catch.

>
>> +	switch (reg_width) {
>> +	case 4:
>> +		uart->port.iotype = UPIO_MEM32;
>> +		break;
>> +
>> +	case 2:
>> +		uart->port.iotype = UPIO_MEM16;
>> +		break;
>> +
>> +	default:
>> +		dev_err(dev, "invalid reg_width %lld\n", reg_width);
>
> unsupported ?
>
>> +		return -EINVAL;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int dfl_uart_probe(struct dfl_device *dfl_dev)
>> +{
>> +	struct device *dev = &dfl_dev->dev;
>> +	struct uart_8250_port uart;
>> +	struct dfl_uart *dfluart;
>> +	resource_size_t res_size;
>> +	void __iomem *dfh_base;
>> +	int ret;
>> +
>> +	memset(&uart, 0, sizeof(uart));
>> +	uart.port.flags = UPF_IOREMAP;
>> +	uart.port.mapbase = dfl_dev->csr_res.start;
>> +	uart.port.mapsize = resource_size(&dfl_dev->csr_res);
>> +
>> +	dfluart = devm_kzalloc(dev, sizeof(*dfluart), GFP_KERNEL);
>> +	if (!dfluart)
>> +		return -ENOMEM;
>> +
>> +	dfh_base = devm_ioremap_resource(dev, &dfl_dev->mmio_res);
>> +	if (IS_ERR(dfh_base))
>> +		return PTR_ERR(dfh_base);
>> +
>> +	res_size = resource_size(&dfl_dev->mmio_res);
>> +
>> +	ret = dfl_uart_get_params(dev, dfh_base, res_size, &uart);
>> +
>> +	devm_iounmap(dev, dfh_base);
>> +	devm_release_mem_region(dev, dfl_dev->mmio_res.start, res_size);
>> +
>> +	if (ret < 0)
>> +		return dev_err_probe(dev, ret, "failed uart feature walk\n");
>> +
>> +	dev_dbg(dev, "nr_irqs %d %p\n", dfl_dev->num_irqs, dfl_dev->irqs);
>> +
>> +	if (dfl_dev->num_irqs == 1)
>> +		uart.port.irq = dfl_dev->irqs[0];
>> +
>> +	/* register the port */
>
> This comment is pretty useless. Just drop it.

Will drop this useless comment.

>
>> +	dfluart->line = serial8250_register_8250_port(&uart);
>> +	if (dfluart->line < 0)
>> +		return dev_err_probe(dev, dfluart->line, "unable to register 8250 port.\n");
>> +
>> +	dev_info(dev, "serial8250_register_8250_port %d\n", dfluart->line);
>
> This you want to drop too. It seems a debug thing rather than info level
> stuff.

It is actually redundant output because serial8250_register_8250_port() 
produces useful output.  I will drop the line.

>
>
> -- 
> i.
>
>