Commit c432df15 authored by Johan Hovold's avatar Johan Hovold
Browse files

USB: serial: ch341: fix lockup of devices with limited prescaler 



Michael Hanselmann reports that

	[a] subset of all CH341 devices stop responding to bulk
	transfers, usually after the third byte, when the highest
	prescaler bit (0b100) is set. There is one exception, namely a
	prescaler of exactly 0b111 (fact=1, ps=3).

Fix this by forcing a lower base clock (fact = 0) whenever needed.

This specifically makes the standard rates 110, 134 and 200 bps work
again with these devices.

Fixes: 35714565 ("USB: serial: ch341: reimplement line-speed handling")
Cc: stable <stable@vger.kernel.org>	# 5.5
Reported-by: default avatarMichael Hanselmann <public@hansmi.ch>
Link: https://lore.kernel.org/r/20200514141743.GE25962@localhost


Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
parent c404bf4a

drivers/usb/serial/ch341.c

+12 −3
Original line number Diff line number Diff line
@@ -73,6 +73,8 @@ 
#define CH341_LCR_CS6          0x01

#define CH341_LCR_CS5          0x00



#define CH341_QUIRK_LIMITED_PRESCALER	BIT(0)



static const struct usb_device_id id_table[] = {

	{ USB_DEVICE(0x4348, 0x5523) },

	{ USB_DEVICE(0x1a86, 0x7523) },
@@ -160,9 +162,11 @@ 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(speed_t speed)

static int ch341_get_divisor(struct ch341_private *priv)

{

	unsigned int fact, div, clk_div;

	speed_t speed = priv->baud_rate;

	bool force_fact0 = false;

	int ps;



	/*
@@ -188,8 +192,12 @@ static int ch341_get_divisor(speed_t speed) 
	clk_div = CH341_CLK_DIV(ps, fact);

	div = CH341_CLKRATE / (clk_div * speed);



	/* Some devices require a lower base clock if ps < 3. */

	if (ps < 3 && (priv->quirks & CH341_QUIRK_LIMITED_PRESCALER))

		force_fact0 = true;



	/* Halve base clock (fact = 0) if required. */

	if (div < 9 || div > 255) {

	if (div < 9 || div > 255 || force_fact0) {

		div /= 2;

		clk_div *= 2;

		fact = 0;
@@ -228,7 +236,7 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev, 
	if (!priv->baud_rate)

		return -EINVAL;



	val = ch341_get_divisor(priv->baud_rate);

	val = ch341_get_divisor(priv);

	if (val < 0)

		return -EINVAL;
@@ -333,6 +341,7 @@ 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;

		r = 0;

		goto out;

	}

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