Re: [PATCH v4 4/4] tty: serial: 8250: add DFL bus driver for Altera 16550.

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On Sat, 29 Oct 2022, Xu Yilun wrote:

On 2022-10-20 at 14:26:10 -0700, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
From: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>

Add a Device Feature List (DFL) bus driver for the Altera
16550 implementation of UART.

Signed-off-by: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
v4: use dev_err_probe() everywhere that is appropriate
    clean up noise
    change error messages to use the word, unsupported
    tried again to sort Makefile and KConfig better
    reorder probe function for easier error handling
    use new dfh_find_param API

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 | 149 +++++++++++++++++++++++++++++
 drivers/tty/serial/8250/Kconfig    |  12 +++
 drivers/tty/serial/8250/Makefile   |   1 +
 3 files changed, 162 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..f02f0ba2a565
--- /dev/null
+++ b/drivers/tty/serial/8250/8250_dfl.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: GPL-2.0
+ * Driver for FPGA UART
+ *
+ * Copyright (C) 2022 Intel Corporation, Inc.
+ *
+ * Authors:
+ *   Ananda Ravuri <ananda.ravuri@xxxxxxxxx>
+ *   Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
+ */
+#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 {
+	int line;
+static int dfl_uart_get_params(struct dfl_device *dfl_dev, struct uart_8250_port *uart)
+	struct device *dev = &dfl_dev->dev;
+	u64 v, fifo_len, reg_width;
+	u64 *p;
+	p = dfh_find_param(dfl_dev, DFHv1_PARAM_ID_CLK_FRQ);
+	if (!p)
+		return dev_err_probe(dev, -EINVAL, "missing CLK_FRQ param\n");
+	uart->port.uartclk = *p;
+	dev_dbg(dev, "UART_CLK_ID %u Hz\n", uart->port.uartclk);
+	p = dfh_find_param(dfl_dev, DFHv1_PARAM_ID_FIFO_LEN);
+	if (!p)
+		return dev_err_probe(dev, -EINVAL, "missing FIFO_LEN param\n");
+	fifo_len = *p;
+	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:
+		return dev_err_probe(dev, -EINVAL, "unsupported fifo_len %llu\n", fifo_len);
+	}
+	p = dfh_find_param(dfl_dev, DFHv1_PARAM_ID_REG_LAYOUT);
+	if (!p)
+		return dev_err_probe(dev, -EINVAL, "missing REG_LAYOUT param\n");
+	v = *p;
+	uart->port.regshift = FIELD_GET(DFHv1_PARAM_ID_REG_SHIFT, v);
+	reg_width = FIELD_GET(DFHv1_PARAM_ID_REG_WIDTH, v);

I have concern that the raw layout inside the parameter block is
still exposed to drivers and need to be parsed by each driver.

Raw parameter block will always have to be passed to the driver because HW specific properties can be defined that will need to be parsed by the specific driver.

How about we define HW agnostic IDs for parameter specific fields like:


And define like u64 dfl_find_param(struct dfl_device *, int param_id, int field_id)

I don't think dfl_find_param as defined above adds much value.

Think further, if we have to define HW agnostic property - value pairs,
why don't we just use "Software nodes for the firmware node", see
drivers/base/swnode.c. I think this may be a better choice.

I am looking into "Software nodes for the firmware node", and it can be used for HW agnostic properties. Each dfl driver will still have to make a function call to fetch each HW agnostice property value as well as a function call to find the HW specific parameters and then parse those parameters.


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