On 14.05.20 16:47, Johan Hovold wrote:
> On Tue, Mar 31, 2020 at 11:37:22PM +0000, Michael Hanselmann wrote:
>> static int ch341_set_baudrate_lcr(struct usb_device *dev,
>> - struct ch341_private *priv, u8 lcr)
>> + struct ch341_private *priv,
>> + unsigned baud_rate, u8 lcr)
>
> Use speed_t.
Done. ch341_private.baud_rate and ch341_set_termios also use unsigned
though. Should those also be changed to speed_t?
>> + r = ch341_set_baudrate_lcr(port->serial->dev, priv,
>> + CH341_MIN_BPS,
>> + CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX |
>
> Hmm. This would corrupt incoming data as well during the break.
Yes, there's no way to avoid that. In my opinion being able to send a
break signal for a serial console interrupt (SysRq) outweighs the
corruption. Updated the comment on ch341_simulate_break to mention
the caveat.
>> + dev_dbg(&port->dev, "%s - Leave break state requested\n", __func__);
>> +
>> + if (time_before(jiffies, priv->break_end)) {
>> + /* Wait until NUL byte is written */
>> + delay = min_t(unsigned long, HZ, priv->break_end - jiffies);
>
> Looks like this can underflow if you're preempted after the check.
Moved the subtraction before the min_t macro to only evaluate it once.
>> + if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) {
>> + dev_warn_once(&port->dev,
>> + "%s - hardware doesn't support real break"
>> + " condition, simulating instead\n",
>> + __func__);
>
> Don't break the string, and drop the __func__.
Done, also for the other error messages you pointed out.
Michael
---
>From 94fec46e814276491c9a027c5d3912b68deb9c55 Mon Sep 17 00:00:00 2001
From: Michael Hanselmann <public@xxxxxxxxx>
Date: Thu, 5 Mar 2020 01:50:35 +0100
Subject: [PATCH 2/2] USB: serial: ch341: Simulate break condition if not
supported
A subset of all CH341 devices don't support a real break condition. This
fact is already used in the "ch341_detect_quirks" function. With this
change a quirk is implemented to simulate a break condition by
temporarily lowering the baud rate and sending a NUL byte.
The primary drawbacks of this approach are that the duration of the
break can't be controlled by userland and that data incoming during
a simulated break is corrupted.
The "TTY_DRIVER_HARDWARE_BREAK" serial driver flag was investigated as
an alternative. It's a driver-wide flag and would've required
significant changes to the serial and USB-serial driver frameworks to
expose it for individual USB-serial adapters.
Tested by sending a break condition and watching the TX pin using an
oscilloscope.
Signed-off-by: Michael Hanselmann <public@xxxxxxxxx>
---
drivers/usb/serial/ch341.c | 105 ++++++++++++++++++++++++++++++++++---
1 file changed, 97 insertions(+), 8 deletions(-)
diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 202cfa4ef6c7..1e63310cfd9c 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -78,6 +78,7 @@
#define CH341_LCR_CS5 0x00
#define CH341_QUIRK_LIMITED_PRESCALER BIT(0)
+#define CH341_QUIRK_SIMULATE_BREAK BIT(1)
static const struct usb_device_id id_table[] = {
{ USB_DEVICE(0x4348, 0x5523) },
@@ -94,6 +95,7 @@ struct ch341_private {
u8 msr;
u8 lcr;
unsigned long quirks;
+ unsigned long break_end;
};
static void ch341_set_termios(struct tty_struct *tty,
@@ -168,10 +170,9 @@ static const speed_t ch341_min_rates[] = {
* 2 <= div <= 256 if fact = 0, or
* 9 <= div <= 256 if fact = 1
*/
-static int ch341_get_divisor(struct ch341_private *priv)
+static int ch341_get_divisor(struct ch341_private *priv, speed_t speed)
{
unsigned int fact, div, clk_div;
- speed_t speed = priv->baud_rate;
bool force_fact0 = false;
int ps;
@@ -234,15 +235,16 @@ static int ch341_get_divisor(struct ch341_private *priv)
}
static int ch341_set_baudrate_lcr(struct usb_device *dev,
- struct ch341_private *priv, u8 lcr)
+ struct ch341_private *priv,
+ speed_t baud_rate, u8 lcr)
{
int val;
int r;
- if (!priv->baud_rate)
+ if (!baud_rate)
return -EINVAL;
- val = ch341_get_divisor(priv);
+ val = ch341_get_divisor(priv, baud_rate);
if (val < 0)
return -EINVAL;
@@ -322,7 +324,7 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
if (r < 0)
goto out;
- r = ch341_set_baudrate_lcr(dev, priv, priv->lcr);
+ r = ch341_set_baudrate_lcr(dev, priv, priv->baud_rate, priv->lcr);
if (r < 0)
goto out;
@@ -356,7 +358,7 @@ static int ch341_detect_quirks(struct usb_serial_port *port)
CH341_REG_BREAK, 0, buffer, size, DEFAULT_TIMEOUT);
if (r == -EPIPE) {
dev_dbg(&port->dev, "break control not supported\n");
- quirks = CH341_QUIRK_LIMITED_PRESCALER;
+ quirks = CH341_QUIRK_LIMITED_PRESCALER | CH341_QUIRK_SIMULATE_BREAK;
r = 0;
goto out;
}
@@ -537,7 +539,8 @@ static void ch341_set_termios(struct tty_struct *tty,
if (baud_rate) {
priv->baud_rate = baud_rate;
- r = ch341_set_baudrate_lcr(port->serial->dev, priv, lcr);
+ r = ch341_set_baudrate_lcr(port->serial->dev, priv,
+ priv->baud_rate, lcr);
if (r < 0 && old_termios) {
priv->baud_rate = tty_termios_baud_rate(old_termios);
tty_termios_copy_hw(&tty->termios, old_termios);
@@ -556,15 +559,101 @@ static void ch341_set_termios(struct tty_struct *tty,
ch341_set_handshake(port->serial->dev, priv->mcr);
}
+/*
+ * A subset of all CH34x devices don't support a real break condition and
+ * reading CH341_REG_BREAK fails (see also ch341_detect_quirks). This function
+ * simulates a break condition by lowering the baud rate to the minimum
+ * supported by the hardware upon enabling the break condition and sending
+ * a NUL byte.
+ *
+ * Incoming data is corrupted while the break condition is being simulated.
+ *
+ * Normally the duration of the break condition can be controlled individually
+ * by userspace using TIOCSBRK and TIOCCBRK or by passing an argument to
+ * TCSBRKP. Due to how the simulation is implemented the duration can't be
+ * controlled. The duration is always about (1s / 46bd * 9bit) = 196ms.
+ */
+static void ch341_simulate_break(struct tty_struct *tty, int break_state)
+{
+ struct usb_serial_port *port = tty->driver_data;
+ struct ch341_private *priv = usb_get_serial_port_data(port);
+ unsigned long delay;
+ int r;
+
+ if (break_state != 0) {
+ dev_dbg(&port->dev, "enter break state requested\n");
+
+ r = ch341_set_baudrate_lcr(port->serial->dev, priv,
+ CH341_MIN_BPS,
+ CH341_LCR_ENABLE_RX | CH341_LCR_ENABLE_TX |
+ CH341_LCR_CS8);
+ if (r < 0) {
+ dev_err(&port->dev,
+ "failed to change baud rate to %u: %d\n",
+ CH341_MIN_BPS, r);
+ goto restore;
+ }
+
+ r = tty_put_char(tty, '\0');
+ if (r < 0) {
+ dev_err(&port->dev,
+ "failed to write NUL byte for simulated break condition: %d\n",
+ r);
+ goto restore;
+ }
+
+ /*
+ * Compute how long transmission will take and add a bit of
+ * safety margin.
+ */
+ priv->break_end = jiffies + (10 * HZ / CH341_MIN_BPS);
+
+ return;
+ }
+
+ dev_dbg(&port->dev, "leave break state requested\n");
+
+ if (time_before(jiffies, priv->break_end)) {
+ /*
+ * Wait until NUL byte is written and limit delay to one second
+ * at most.
+ */
+ delay = priv->break_end - jiffies;
+ delay = min_t(unsigned long, HZ, delay);
+
+ dev_dbg(&port->dev,
+ "wait %d ms while transmitting NUL byte at %u baud\n",
+ jiffies_to_msecs(delay), CH341_MIN_BPS);
+ schedule_timeout_interruptible(delay);
+ }
+
+restore:
+ /* Restore original baud rate */
+ r = ch341_set_baudrate_lcr(port->serial->dev, priv, priv->baud_rate,
+ priv->lcr);
+ if (r < 0)
+ dev_err(&port->dev,
+ "restoring original baud rate of %u failed: %d\n",
+ priv->baud_rate, r);
+}
+
static void ch341_break_ctl(struct tty_struct *tty, int break_state)
{
const uint16_t ch341_break_reg =
((uint16_t) CH341_REG_LCR << 8) | CH341_REG_BREAK;
struct usb_serial_port *port = tty->driver_data;
+ struct ch341_private *priv = usb_get_serial_port_data(port);
int r;
uint16_t reg_contents;
uint8_t *break_reg;
+ if (priv->quirks & CH341_QUIRK_SIMULATE_BREAK) {
+ dev_warn_once(&port->dev,
+ "hardware doesn't support real break condition, simulating instead\n");
+ ch341_simulate_break(tty, break_state);
+ return;
+ }
+
break_reg = kmalloc(2, GFP_KERNEL);
if (!break_reg)
return;
--
2.20.1
