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USB: serial: ch341: add min and max line-speed macros

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The line-speed algorithm clamps the requested value to the supported
range instead of bailing out on unsupported values.

Provide min and max macros and indicate how they are derived instead of
hardcoding the limits.

Note that the algorithm depends on the minimum rate (45.78 bps)
being rounded up (and the maximum rate being rounded down) to avoid
special casing.

Suggested-by: Michael Hanselmann <public@hansmi.ch>
Link: https://lore.kernel.org/r/20200630095756.GZ3334@localhost
Signed-off-by: Johan Hovold <johan@kernel.org>
This commit is contained in:
Johan Hovold 2020-06-30 11:57:56 +02:00
parent 2c509d1cc8
commit 86f6da2951
1 changed files with 5 additions and 1 deletions
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6
drivers/usb/serial/ch341.c
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@ -156,6 +156,10 @@ static const speed_t ch341_min_rates[] = {
CH341_MIN_RATE(3),
};
/* Supported range is 46 to 3000000 bps. */
#define CH341_MIN_BPS DIV_ROUND_UP(CH341_CLKRATE, CH341_CLK_DIV(0, 0) * 256)
#define CH341_MAX_BPS (CH341_CLKRATE / (CH341_CLK_DIV(3, 0) * 2))
/*
* The device line speed is given by the following equation:
*
@ -177,7 +181,7 @@ static int ch341_get_divisor(struct ch341_private *priv)
* Clamp to supported range, this makes the (ps < 0) and (div < 2)
* sanity checks below redundant.
*/
speed = clamp(speed, 46U, 3000000U);
speed = clamp_val(speed, CH341_MIN_BPS, CH341_MAX_BPS);
/*
* Start with highest possible base clock (fact = 1) that will give a