在 2023/4/14 20:10, Ilpo Järvinen 写道:
On Fri, 14 Apr 2023, qianfan wrote:
Hi:
My custom board is based on allwinner R40, the uart is compatibled with
serial8250. Based on it's datasheet:
When TX transmit data, or RX receives data, or TX FIFO is not empty, then
the
BUSY flag bit can be set to 1 by hardware, which indicates the UART
controller is busy.
We cannot write LCR and DLL to update UART params such as baudrate and partity
while the UART is busy, however `serial8250_do_set_termios` is a void
function,
the upper level always assume the uart params is updated.
The upper level `uart_set_termios` do noting if ktermios params is not
changed,
it will not update when the user space program running tcsetattr set a same
baudrate again.
So we can not fix the baudrate when
`serial8250_do_set_termios`
failed.
Allwinner R40's datasheet provided a way for this case.
CHCFG_AT_BUSY(configure at busy): Enable the bit, software can also set UART
controller when UART is busy, such as the LCR, DLH, DLL register.
CHANGE_UPDATE(change update): If CHCFG_AT_BUSY is enabled, and CHANGE_UPDATE
is written to 1, the configuration of UART controller can be updated.
After completed update, the bit is cleared to 0 automatically.
I can't know this feature is expanded by allwinner, or it is a common
functiton
of serial8250. Perhaps the serial8250 driver need this.
tcsetattr() can be given a flag which enforces TX empty condition before
core calls into the lower layer HW set_termios function. Would that be
enough to solve the case you're interested in?
Obviously, nothing can prevent Rx from occuring as it's not under local
UART's control (e.g. a busy flag check would still be racy). But does
writing those registers actually break something or just corrupts the
character under Tx/Rx (which can be handled by flushing)?
Hi:
I speed long times to create a common solution for this problem.
(I had create two commit, the first one add some sysfs debug interface
and the second one try solve this problem. So the next following patch
has only patch-2. Let's we discuess this solution and I will send all
patches if it is good.)
Allwinner introduce some bits in HALT_TX register which can change
baudrate while the serial is busy. But that is not a common feature
of dw-uart. Rockchip's uart is also based on dw-uart and they doesn't
has such feature.
The loopback is a common feature of 16450/16550 serial, so we can set
loopback mode to cut down the external serial line to force the serial
to idle.
Next is the second patch:
From 171e981c3695e3efcc76a2c4f0d0937d366d6e2a Mon Sep 17 00:00:00 2001
From: qianfan Zhao <qianfanguijin@xxxxxxx>
Date: Fri, 5 May 2023 08:46:50 +0800
Subject: [PATCH] drivers: serial: 8250_dw: Make uart idle before set
baudrate
Some registers which control the baudrate such as DLL, DLM can not
write while the uart is busy. So set the controller to loopback mode
and clear fifos to force idle before change baudrate.
Signed-off-by: qianfan Zhao <qianfanguijin@xxxxxxx>
---
drivers/tty/serial/8250/8250_dw.c | 57 ++++++++++++++++++++++++++++++-
1 file changed, 56 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/8250/8250_dw.c
b/drivers/tty/serial/8250/8250_dw.c
index 3dca344ca19c..4eaa4d05a43e 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -35,6 +35,7 @@
#define DW_UART_USR 0x1f /* UART Status Register */
/* DesignWare specific register fields */
+#define DW_UART_USR_BUSY BIT(0)
#define DW_UART_MCR_SIRE BIT(6)
struct dw8250_data {
@@ -43,6 +44,8 @@ struct dw8250_data {
u8 usr_reg;
int msr_mask_on;
int msr_mask_off;
+ u8 dll;
+ u8 dlm;
struct clk *clk;
struct clk *pclk;
struct notifier_block clk_notifier;
@@ -52,7 +55,9 @@ struct dw8250_data {
unsigned int skip_autocfg:1;
unsigned int uart_16550_compatible:1;
+ unsigned int last_loopback_waiting_time;
unsigned long iir_busy_count;
+ unsigned long lcr_busy_count;
};
static inline struct dw8250_data *to_dw8250_data(struct
dw8250_port_data *data)
@@ -93,6 +98,7 @@ static void dw8250_force_idle(struct uart_port *p)
static void dw8250_check_lcr(struct uart_port *p, int value)
{
+ struct dw8250_data *d = to_dw8250_data(p->private_data);
void __iomem *offset = p->membase + (UART_LCR << p->regshift);
int tries = 1000;
@@ -121,6 +127,7 @@ static void dw8250_check_lcr(struct uart_port *p,
int value)
* FIXME: this deadlocks if port->lock is already held
* dev_err(p->dev, "Couldn't set LCR to %d\n", value);
*/
+ d->lcr_busy_count++;
}
/* Returns once the transmitter is empty or we run out of retries */
@@ -360,6 +367,46 @@ static void dw8250_set_termios(struct uart_port *p,
struct ktermios *termios,
serial8250_do_set_termios(p, termios, old);
}
+static void dw8250_set_divisor(struct uart_port *p, unsigned int baud,
+ unsigned int quot, unsigned int quot_frac)
+{
+ struct uart_8250_port *up = up_to_u8250p(p);
+ struct dw8250_data *d = to_dw8250_data(p->private_data);
+ unsigned int usr;
+ int retries;
+
+ /*
+ * LCR, DLL, DLM registers can not write while the uart is busy,
+ * set uart to loopback mode, clear fifos to force idle.
+ * The loopback mode doesn't take effect immediately, it will waiting
+ * current byte received done, the lower baudrate the longer waiting
+ * time.
+ */
+ p->serial_out(p, UART_MCR, up->mcr | UART_MCR_LOOP);
+ for (retries = 0; retries < 10000; retries++) {
+ dw8250_force_idle(p);
+
+ usr = p->serial_in(p, d->usr_reg);
+ if (!(usr & DW_UART_USR_BUSY))
+ break;
+ udelay(1);
+ }
+
+ d->last_loopback_waiting_time = retries;
+
+ p->serial_out(p, UART_LCR, up->lcr | UART_LCR_DLAB);
+ if (p->serial_in(p, UART_LCR) & UART_LCR_DLAB) {
+ d->dll = quot & 0xff;
+ d->dlm = (quot >> 8) & 0xff;
+
+ p->serial_out(p, UART_DLL, d->dll);
+ p->serial_out(p, UART_DLM, d->dlm);
+ p->serial_out(p, UART_LCR, up->lcr);
+ }
+
+ p->serial_out(p, UART_MCR, up->mcr);
+}
+
static void dw8250_set_ldisc(struct uart_port *p, struct ktermios
*termios)
{
struct uart_8250_port *up = up_to_u8250p(p);
@@ -449,6 +496,8 @@ static ssize_t register_show(struct device *dev,
struct device_attribute *attr,
spin_lock_irqsave(&p->lock, flags);
ret = scnprintf(buf, PAGE_SIZE,
+ "%s: %02x\n"
+ "%s: %02x\n"
"%s: %02x/%02x\n"
"%s: %02x\n"
"%s: %02x\n"
@@ -458,6 +507,8 @@ static ssize_t register_show(struct device *dev,
struct device_attribute *attr,
"%s: %02x\n"
"%s: %02x\n"
,
+ "DLL", d->dll,
+ "DLM", d->dlm,
"IER", up->ier, p->serial_in(p, UART_IER),
"IIR", p->serial_in(p, UART_IIR),
"FCR", up->fcr,
@@ -478,7 +529,10 @@ static ssize_t busy_show(struct device *dev, struct
device_attribute *attr,
{
struct dw8250_data *d = platform_get_drvdata(to_platform_device(dev));
- return scnprintf(buf, PAGE_SIZE, "%lu\n", d->iir_busy_count);
+ return scnprintf(buf, PAGE_SIZE, "%lu %lu %u\n",
+ d->iir_busy_count,
+ d->lcr_busy_count,
+ d->last_loopback_waiting_time);
}
static DEVICE_ATTR_RO(busy);
@@ -570,6 +624,7 @@ static int dw8250_probe(struct platform_device *pdev)
p->serial_out = dw8250_serial_out;
p->set_ldisc = dw8250_set_ldisc;
p->set_termios = dw8250_set_termios;
+ p->set_divisor = dw8250_set_divisor;
p->membase = devm_ioremap(dev, regs->start, resource_size(regs));
if (!p->membase)
--
2.25.1
