Re: [PATCH v2 6/6] tty: serial: 8250: add DFL bus driver for Altera 16550.

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

On Fri, 23 Sep 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>
> ---
> 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 +
>  include/linux/dfl.h                |   7 ++
>  4 files changed, 194 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..539ca6138eda
> --- /dev/null
> +++ b/drivers/tty/serial/8250/8250_dfl.c
> @@ -0,0 +1,177 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for FPGA UART
> + *
> + * Copyright (C) 2022 Intel Corporation, Inc.
> + *
> + * Authors:
> + *   Ananda Ravuri <ananda.ravuri@intel.com>
> + *   Matthew Gerlach <matthew.gerlach@linux.intel.com>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/dfl.h>
> +#include <linux/io-64-nonatomic-lo-hi.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/serial.h>
> +#include <linux/serial_8250.h>
> +
> +struct dfl_uart {
> +	void __iomem   *csr_base;
> +	struct device  *dev;
> +	u64             uart_clk;
> +	u64             fifo_len;
> +	unsigned int    fifo_size;
> +	unsigned int    reg_shift;

Why to make this intermediate storage for these values, wouldn't it be 
simpler to just fill them into the uart_port directly?

> +	unsigned int    line;
> +};
> +
> +static int feature_uart_walk(struct dfl_uart *dfluart, resource_size_t max)
> +{
> +	void __iomem *param_base;
> +	int off;
> +	u64 v;
> +
> +	v = readq(dfluart->csr_base + DFHv1_CSR_SIZE_GRP);
> +
> +	if (!FIELD_GET(DFHv1_CSR_SIZE_GRP_HAS_PARAMS, v)) {
> +		dev_err(dfluart->dev, "missing required DFH parameters\n");
> +		return -EINVAL;
> +	}
> +
> +	param_base = dfluart->csr_base + DFHv1_PARAM_HDR;

Are all callers of dfl_find_param() expected to run these same checks and
calculations? Perhaps some helper to find param base would be useful and
it could also run those checks.

> +	off = dfl_find_param(param_base, max, DFHv1_PARAM_ID_CLK_FRQ);
> +	if (off < 0) {
> +		dev_err(dfluart->dev, "missing CLK_FRQ param\n");
> +		return -EINVAL;
> +	}
> +
> +	dfluart->uart_clk = readq(param_base + off + DFHv1_PARAM_DATA);
> +	dev_dbg(dfluart->dev, "UART_CLK_ID %llu Hz\n", dfluart->uart_clk);
> +
> +	off = dfl_find_param(param_base, max, DFHv1_PARAM_ID_FIFO_LEN);
> +	if (off < 0) {
> +		dev_err(dfluart->dev, "missing FIFO_LEN param\n");
> +		return -EINVAL;
> +	}
> +
> +	dfluart->fifo_len = readq(param_base + off + DFHv1_PARAM_DATA);
> +	dev_dbg(dfluart->dev, "UART_FIFO_ID fifo_len %llu\n", dfluart->fifo_len);
> +
> +	off = dfl_find_param(param_base, max, DFHv1_PARAM_ID_REG_LAYOUT);
> +	if (off < 0) {
> +		dev_err(dfluart->dev, "missing REG_LAYOUT param\n");
> +		return -EINVAL;
> +	}
> +
> +	v = readq(param_base + off + DFHv1_PARAM_DATA);
> +	dfluart->fifo_size = FIELD_GET(DFHv1_PARAM_ID_REG_WIDTH, v);

???

> +	dfluart->reg_shift = FIELD_GET(DFHv1_PARAM_ID_REG_SHIFT, v);
> +	dev_dbg(dfluart->dev, "UART_LAYOUT_ID width %d shift %d\n",
> +		dfluart->fifo_size, dfluart->reg_shift);
> +
> +	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;
> +	int ret;
> +
> +	memset(&uart, 0, sizeof(uart));
> +
> +	dfluart = devm_kzalloc(dev, sizeof(*dfluart), GFP_KERNEL);
> +	if (!dfluart)
> +		return -ENOMEM;
> +
> +	dfluart->dev = dev;
> +
> +	dfluart->csr_base = devm_ioremap_resource(dev, &dfl_dev->mmio_res);
> +	if (IS_ERR(dfluart->csr_base)) {
> +		return PTR_ERR(dfluart->csr_base);
> +	}

No need for braces.

> +static void dfl_uart_remove(struct dfl_device *dfl_dev)
> +{
> +	struct dfl_uart *dfluart = dev_get_drvdata(&dfl_dev->dev);
> +
> +	if (dfluart->line > 0)

Line 0 is valid uart port. Perhaps you'd never see it here due to how the 
8250 driver allocs ports but it would be better to not make this kind of 
assumption.

> +		serial8250_unregister_port(dfluart->line);
> +}

> diff --git a/include/linux/dfl.h b/include/linux/dfl.h
> index 7d74ef8d1d20..a17aeccc501e 100644
> --- a/include/linux/dfl.h
> +++ b/include/linux/dfl.h
> @@ -67,6 +67,13 @@
>  #define DFHv1_PARAM_MSIX_STARTV	0x8
>  #define DFHv1_PARAM_MSIX_NUMV	0xc
>  
> +#define DFHv1_PARAM_ID_CLK_FRQ    0x2
> +#define DFHv1_PARAM_ID_FIFO_LEN   0x3
> +
> +#define DFHv1_PARAM_ID_REG_LAYOUT 0x4
> +#define DFHv1_PARAM_ID_REG_WIDTH  GENMASK_ULL(63, 32)
> +#define DFHv1_PARAM_ID_REG_SHIFT  GENMASK_ULL(31, 0)

Should UART be included into these names or are they intended to be more 
generic parameters (for non-UART uses)?


-- 
 i.