From: Michael Hanselmann <public@hansmi.ch>
To: linux-usb@vger.kernel.org, Johan Hovold <johan@kernel.org>
Cc: Michael Hanselmann <public@hansmi.ch>,
Michael Dreher <michael@5dot1.de>,
Jonathan Olds <jontio@i4free.co.nz>
Subject: [PATCH v2 5/6] USB: serial: ch341: Compute minimum baud rate
Date: Tue, 31 Mar 2020 23:37:21 +0000 [thread overview]
Message-ID: <55c53ab4650ecabd1a6cd619ec72eed2e00d5dd2.1585697281.git.public@hansmi.ch> (raw)
In-Reply-To: <cover.1585697281.git.public@hansmi.ch>
The minimum baud rate was hardcoded, not computed. A patch later in the
series will make use of the minimum baud rate as well.
The (1 + ((x - 1) / y)) pattern is to force rounding up (mathematically
the minimum rate is about 45.78bps).
Signed-off-by: Michael Hanselmann <public@hansmi.ch>
---
drivers/usb/serial/ch341.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 9407e12d9fbc..c820772e6a07 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -147,6 +147,8 @@ static int ch341_control_in(struct usb_device *dev,
#define CH341_CLKRATE 48000000
#define CH341_CLK_DIV(ps, fact) (1 << (12 - 3 * (ps) - (fact)))
+#define CH341_MIN_BPS \
+ (unsigned int)(1 + (((CH341_CLKRATE) - 1) / (CH341_CLK_DIV(0, 0) * 256)))
#define CH341_MIN_RATE(ps, fact) \
(CH341_CLKRATE / (CH341_CLK_DIV((ps), (fact)) * 256))
@@ -210,10 +212,10 @@ static int ch341_get_divisor(struct ch341_private *priv)
speed = priv->baud_rate;
/*
- * Clamp to supported range, this makes the (ps < 0) and (div < 2)
- * sanity checks below redundant.
+ * Clamp to supported range, making the later range sanity checks
+ * redundant.
*/
- speed = clamp(speed, 46U, 3000000U);
+ speed = clamp(speed, CH341_MIN_BPS, 3000000U);
if (priv->quirks & CH341_QUIRK_LIMITED_PRESCALER) {
/*
--
2.20.1
next prev parent reply other threads:[~2020-03-31 23:37 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-31 23:37 [PATCH v2 0/6] USB: serial: ch341: Add support for limited chips (was: Add support for HL340 devices) Michael Hanselmann
2020-03-31 23:37 ` [PATCH v2 1/6] USB: serial: ch341: Reduce special cases in clock calculation Michael Hanselmann
2020-03-31 23:37 ` [PATCH v2 2/6] USB: serial: ch341: Add basis for quirk detection Michael Hanselmann
2020-05-14 14:09 ` Johan Hovold
2020-03-31 23:37 ` [PATCH v2 3/6] USB: serial: ch341: Limit prescaler on quirky chips Michael Hanselmann
2020-05-14 14:17 ` Johan Hovold
2020-05-27 13:16 ` Johan Hovold
2020-05-27 15:41 ` Michael Hanselmann
2020-05-29 7:15 ` Johan Hovold
2020-03-31 23:37 ` [PATCH v2 4/6] USB: serial: ch341: Name prescaler, divisor registers Michael Hanselmann
2020-05-14 14:24 ` Johan Hovold
2020-05-27 20:59 ` Michael Hanselmann
2020-06-29 9:51 ` Johan Hovold
2020-03-31 23:37 ` Michael Hanselmann [this message]
2020-05-27 22:19 ` [PATCH v2 5/6] USB: serial: ch341: Compute minimum baud rate Michael Hanselmann
2020-06-30 9:57 ` Johan Hovold
2020-03-31 23:37 ` [PATCH v2 6/6] USB: serial: ch341: Simulate break condition if not supported Michael Hanselmann
2020-05-14 14:47 ` Johan Hovold
2020-05-27 22:21 ` Michael Hanselmann
2020-06-30 11:39 ` Johan Hovold
2020-07-04 18:25 ` Michael Hanselmann
2020-07-06 9:31 ` Johan Hovold
2020-05-14 14:02 ` [PATCH v2 0/6] USB: serial: ch341: Add support for limited chips (was: Add support for HL340 devices) Johan Hovold
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