[PATCH v3 11/11] serial: sc16is7xx: add dump registers function

[Hugo Villeneuve <hugo@xxxxxxxxxxx>]

From: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>

With this driver, it is very hard to debug the registers using
the /sys/kernel/debug/regmap interface.

The main reason is that bits 0 and 1 of the register address
correspond to the channels bits, so the register address itself starts
at bit 2, so we must 'mentally' shift each register address by 2 bits
to get its offset.

Also, only channels 0 and 1 are supported, so combinations of bits
0 and 1 being 10b and 11b are invalid, and the display of these
registers is useless.

For example:

cat /sys/kernel/debug/regmap/spi0.0/registers
04: 10 -> Port 0, register offset 1
05: 10 -> Port 1, register offset 1
06: 00 -> Port 2, register offset 1 -> invalid
07: 00 -> port 3, register offset 1 -> invalid
...

Add a debug module parameter to call a custom dump function for each
port registers after the probe phase to help debug.

Signed-off-by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
---
 drivers/tty/serial/sc16is7xx.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 03d00b144304..693b6cc371f8 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -347,6 +347,10 @@ struct sc16is7xx_port {
 	struct sc16is7xx_one		p[];
 };
 
+static bool debug;
+module_param(debug, bool, 0644);
+MODULE_PARM_DESC(debug, "enable/disable debug messages");
+
 static unsigned long sc16is7xx_lines;
 
 static struct uart_driver sc16is7xx_uart = {
@@ -387,6 +391,28 @@ static void sc16is7xx_port_write(struct uart_port *port, u8 reg, u8 val)
 	regmap_write(s->regmap, (reg << SC16IS7XX_REG_SHIFT) | line, val);
 }
 
+static int sc16is7xx_port_dump(struct uart_port *port)
+{
+	int i;
+	unsigned char *buf;
+	char name[64];
+	const int regs_count_per_port = 16;
+
+	buf = devm_kzalloc(port->dev, regs_count_per_port, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	for (i = 0; i < regs_count_per_port; i++)
+		buf[i] = sc16is7xx_port_read(port, i);
+
+	snprintf(name, sizeof(name), "sc16is7xx %s%i: dump ",
+		 sc16is7xx_uart.dev_name, port->line);
+	print_hex_dump(KERN_ERR, name, DUMP_PREFIX_OFFSET, 16, 1,
+		       &((u8 *)buf)[0], regs_count_per_port, 1);
+
+	return 0;
+}
+
 static void sc16is7xx_fifo_read(struct uart_port *port, unsigned int rxlen)
 {
 	struct sc16is7xx_port *s = dev_get_drvdata(port->dev);
@@ -1614,6 +1640,10 @@ static int sc16is7xx_probe(struct device *dev,
 	}
 #endif
 
+	if (debug)
+		for (i = 0; i < devtype->nr_uart; ++i)
+			sc16is7xx_port_dump(&s->p[i].port);
+
 	/*
 	 * Setup interrupt. We first try to acquire the IRQ line as level IRQ.
 	 * If that succeeds, we can allow sharing the interrupt as well.
-- 
2.30.2