diff options
| author | Johan Hovold | 2020-05-14 11:36:45 +0200 |
|---|---|---|
| committer | Johan Hovold | 2020-05-27 15:01:05 +0200 |
| commit | c432df155919582a3cefa35a8f86256c830fa9a4 (patch) | |
| tree | 840012c25e60d3bded15dfa3050434fd28476bfa /drivers/usb | |
| parent | c404bf4aa9236cb4d1068e499ae42acf48a6ff97 (diff) | |
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: 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>
Diffstat (limited to 'drivers/usb')
| -rw-r--r-- | drivers/usb/serial/ch341.c | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c index f2b93f4554a7..89675ee29645 100644 --- 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 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; } |