From: Johan Hovold johan@kernel.org
commit c432df155919582a3cefa35a8f86256c830fa9a4 upstream.
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: 35714565089e ("USB: serial: ch341: reimplement line-speed handling") Cc: stable stable@vger.kernel.org # 5.5 Reported-by: Michael Hanselmann public@hansmi.ch Link: https://lore.kernel.org/r/20200514141743.GE25962@localhost Signed-off-by: Johan Hovold johan@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/usb/serial/ch341.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
--- a/drivers/usb/serial/ch341.c +++ b/drivers/usb/serial/ch341.c @@ -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 spe 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 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 us 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; }